regi.tankonyvtar.hu€¦ · web viewsaturated soil culture 0 9.2. system of rice intensification 0...

Irrigated Farming

Dobos, AttilaMegyes, Attila

Created by XMLmind XSL-FO Converter.

Irrigated Farmingírta Dobos, Attila és Megyes, Attila

TÁMOP-4.1.2.A/1-11/1-2011-0009

University of Debrecen, Service Sciences Methodology Centre

Debrecen, 2013.


TartalomTárgymutató ......................................................................................................................................... 11. 1. INTERACTION BETWEEN WATER MANAGEMENT AND CROP PRODUCTION IN AGRICULTURE .................................................................................................................................. 22. 2. WATER BALANCE OF PLANTS, WATER DEMAND OF PLANTS ...................................... 73. 3. EFFECT OF IRRIGATION ON THE SOIL AND PLANTS .................................................... 104. 4. NECESSITY OF IRRIGATION, EFFICIENCY OF WATER USE .......................................... 205. 5. EVALUATION OF IRRIGATION DOSES ............................................................................... 246. 6. PRINCIPLES OF TILLAGE IN IRRIGATED FARMING ....................................................... 297. 7. PRINCIPLES OF FERTILISATION ON IRRIGATED FIELDS .............................................. 328. 8. IRRIGATION MANAGEMENT OF MAIN CROPS: POTATO .............................................. 35

1. Climate requirements ........................................................................................................... 352. Seasonal water requirements ................................................................................................ 353. Soil requirements .................................................................................................................. 364. Rooting depth and available soil water ................................................................................ 365. Irrigation management ......................................................................................................... 386. Potato growth and irrigation scheduling .............................................................................. 397. Pre-planting to Planting ........................................................................................................ 408. Planting to Pre-emergence (Sprouting) ................................................................................ 409. Emergence to Tuber Initiation (early vine growth) .............................................................. 4110. Tuber Initiation to Full Bloom ........................................................................................... 4111. Full Bloom to Plant Senescence (Tuber Bulking) .............................................................. 4112. Plant Senescence to Harvest ............................................................................................... 4213. Management under limited water supply ........................................................................... 4314. Recommended irrigation methods ..................................................................................... 4315. Irrigation of early forced potato ......................................................................................... 4516. The connection of irrigation with other production technological factors ........................ 4517. The effect of irrigation on yield and the quality of potato ................................................. 4518. Summary ............................................................................................................................ 46

9. 9. IRRIGATION MANAGEMENT OF MAIN CROPS: SUGARBEET ...................................... 471. Climate requirements ........................................................................................................... 472. Seasonal water requirements ................................................................................................ 473. Soil requirements .................................................................................................................. 484. Rooting characteristics and available soil water .................................................................. 485. Irrigation management ......................................................................................................... 506. Early season water management .......................................................................................... 517. Mid-season water management ............................................................................................ 538. Late season water management ............................................................................................ 539. Sprinkler Irrigation Water Management ............................................................................... 5310. Water management impact on disease ................................................................................ 5611. Special requirements of irrigation ...................................................................................... 5612. Summary ............................................................................................................................ 56

10. 10. IRRIGATION MANAGEMENT OF MAIN CROPS: ALFALFA ........................................ 581. Climate requirements ........................................................................................................... 582. Water use characteristics ...................................................................................................... 583. Soil requirements .................................................................................................................. 594. Rooting characteristics ......................................................................................................... 595. Special Alfalfa Irrigation Characteristics ............................................................................. 60


Irrigated Farming

6. Irrigation timing ................................................................................................................... 617. Irrigation scheduling methods .............................................................................................. 628. Crop appearance ................................................................................................................... 639. Calendar method .................................................................................................................. 6310. Crop water use and monitoring soil water status ............................................................... 6311. Evaluation of alfalfa irrigation methods ............................................................................. 6412. Water management impact on diseases .............................................................................. 6513. Summary ............................................................................................................................ 66

11. 11. IRRIGATION MANAGEMENT OF MAIN CROPS: GREEN PEA, SWEET CORN ........ 671. GREEN PEA ........................................................................................................................ 67

1.1. Climate requirements ............................................................................................... 671.2. Seasonal water needs ............................................................................................... 671.3. Soil requirements ..................................................................................................... 681.4. Rooting depth and available water .......................................................................... 681.5. Irrigation management ............................................................................................. 691.6. Irrigation scheduling strategies ................................................................................ 701.7. Vegetative growth .................................................................................................... 70

2. SWEET CORN .................................................................................................................... 712.1. Climate requirements ............................................................................................... 712.2. Soil requirements ..................................................................................................... 722.3. Rooting Depth .......................................................................................................... 722.4. Crop water use ......................................................................................................... 722.5. Irrigation Management ............................................................................................ 732.6. Irrigation Timing ...................................................................................................... 732.7. Vegetative growth .................................................................................................... 732.8. Generative growth ................................................................................................... 73

3. Summary .............................................................................................................................. 7412. 12. IRRIGATION MANAGEMENT OF MAIN CROPS: CORN, CORN SEED ...................... 75

1. CORN ................................................................................................................................... 751.1. Climate requirements ............................................................................................... 751.2. Seasonal water use ................................................................................................... 751.3. Soil requirements ..................................................................................................... 781.4. Rooting characteristics and irrigation ...................................................................... 791.5. Irrigation Scheduling ............................................................................................... 801.6. Irrigation management by growth stage .................................................................. 811.7. Determining the last irrigation for corn ................................................................... 811.8. Irrigation scheduling in different climatic regions .................................................. 82

1.8.1. Humid and Subhumid Region Scheduling .................................................. 821.8.2. Arid and semiarid scheduling ...................................................................... 82

1.9. Irrigation management strategies to conserve water ............................................... 831.9.1. Fully Watered Strategy ................................................................................ 831.9.2. Water Miser Strategy ................................................................................... 831.9.3. Deficit Irrigation Strategy ........................................................................... 84

2. CORN SEED ........................................................................................................................ 842.1. Seasonal water use ................................................................................................... 842.2. Irrigation management ............................................................................................. 84

3. Summary .............................................................................................................................. 8513. 13. IRRIGATION MANAGEMENT OF MAIN CROPS: SOYBEAN ...................................... 86

1. Climate requirements ........................................................................................................... 862. Crop water use ...................................................................................................................... 863. Soil requirements .................................................................................................................. 87


Irrigated Farming

4. Rooting characteristics ......................................................................................................... 875. Water stress and soybean yield ............................................................................................. 876. Soybean growth and irrigation management ........................................................................ 897. Germination and Seedling .................................................................................................... 898. Vegetative growth ................................................................................................................. 909. Flower to full seed ................................................................................................................ 9010. Irrigation termination ......................................................................................................... 9011. Irrigation recommendations ............................................................................................... 9012. Irrigation scheduling .......................................................................................................... 9213. Evaluation methods of irrigation for soybean .................................................................... 9214. Surface irrigations .............................................................................................................. 9215. Sprinkler irrigations ............................................................................................................ 9316. Subsurface drip irrigation ................................................................................................... 9317. Summary ............................................................................................................................ 93

14. 14. IRRIGATION MANAGEMENT OF MAIN CROPS: RICE ................................................ 951. Rice environments ................................................................................................................ 952. Climate requirements ........................................................................................................... 953. Soil requirements .................................................................................................................. 954. Rice rooting characteristics .................................................................................................. 965. Water requirements ............................................................................................................... 96

5.1. Global rice water use ............................................................................................... 965.2. Rice water use and irrigation need at field level ..................................................... 96

6. Field preparation .................................................................................................................. 996.1. Land grading ............................................................................................................ 996.2. Establishing Levees ................................................................................................. 99

7. Sowing methods ................................................................................................................... 997.1. Water planting .......................................................................................................... 997.2. Dry planting ........................................................................................................... 1007.3. Transplantation ...................................................................................................... 100

8. Evaluation of rice irrigation systems ................................................................................. 1018.1. Sprinkler Irrigated Rice ......................................................................................... 1018.2. Multiple Inlet Irrigation ......................................................................................... 101

9. Methods for managing rice water scarcity ........................................................................ 1029.1. Saturated soil culture ............................................................................................. 1029.2. System of Rice Intensification .............................................................................. 1029.3. Alternate wetting and drying ................................................................................. 1039.4. Aerobic rice ........................................................................................................... 1049.5. Raised beds ............................................................................................................ 1049.6. Conservation farming ............................................................................................ 1059.7. What option where? ............................................................................................... 105

10. Sustainability ................................................................................................................... 10511. Environmental impacts ..................................................................................................... 106

11.1. Ammonia volatilization ....................................................................................... 10611.2. Greenhouse gases ................................................................................................ 10611.3. Water pollution .................................................................................................... 10611.4. Effects of water scarcity ...................................................................................... 107

12. Summary .......................................................................................................................... 10715. 15. IRRIGATION MANAGEMENT OF MAIN CROPS: COTTON ....................................... 108

1. Climate requirements ......................................................................................................... 1082. Soil requirements ............................................................................................................... 1083. Cotton rooting characteristics and available soil water ..................................................... 108


Irrigated Farming

4. Crop water use ................................................................................................................... 1095. Water sensitivity of cotton growth stages .......................................................................... 110

5.1. Planting to Emergence ........................................................................................... 1115.2. Emergence to First Square ..................................................................................... 1125.3. First Square to First Flower ................................................................................... 1125.4. First Flower to Peak Bloom ................................................................................... 1125.5. Peak Bloom to Open Bolls .................................................................................... 112

6. Management Considerations for Irrigated Cotton ............................................................. 1126.1. Cotton growth and irrigation management ........................................................... 1126.2. Germination and Seedling Emergence .................................................................. 1136.3. Pre-Squaring Cotton .............................................................................................. 1146.4. Squaring Cotton ..................................................................................................... 1146.5. Early Bloom Cotton ............................................................................................... 1146.6. Cutout, Late Bloom and Boll Opening Cotton ...................................................... 1146.7. Irrigation adds flexibility to farming operations ................................................... 1146.8. Irrigation and Variety Selection ............................................................................. 115

7. Cotton irrigation scheduling ............................................................................................... 1157.1. Water budgeting ..................................................................................................... 1157.2. Sensor-Based Scheduling ...................................................................................... 1167.3. Specific irrigation recommendations for cotton .................................................... 117

8. Irrigation and cotton disease interactions ........................................................................... 1179. Evaluation of cotton irrigation systems ............................................................................. 118

9.1. Subsurface Drip Irrigation ..................................................................................... 1199.2. Surface Drip Irrigation .......................................................................................... 1199.3. Center Pivots ......................................................................................................... 1209.4. Surface Irrigation (Flood/Furrow) ......................................................................... 121

10. Summary .......................................................................................................................... 12116. REFERENCES .......................................................................................................................... 122


Az ábrák listája1.1. Figure 1. Increase of the world population (Source: wikipedia.org) ............................................ 21.2. Figure 2. Global distribution of the world’s water ........................................................................ 21.3. Figure 3. Water use in each sector ................................................................................................. 31.4. Figure 4. Irrigated areas in the world (thousand ha) (Source: commons.wkimedia.org) .............. 42.1. Table 3. Transpiration coefficient of various plants ...................................................................... 82.2. Table 4. Water consumption of the main irrigated plants .............................................................. 92.3. Figure 5. Daily course of water utilisation (Source: Pethő, 1993) ................................................ 93.1. Figure 6. Leakage profiles of soils of various mechanical composition .................................... 123.2. Table 5. Water management of the soil, irrigation method, water norm, connection between the rate and frequency of dosaging (Filep) ..................................................................................................... 153.3. Table 6. Classification of water types from the aspects of usability for irrigation purposes (Darab and Ferenc) ............................................................................................................................................... 153.4. Table 7. Critical groundwater depth and the salt content of the groundwater (Kovda) .............. 163.5. Figure 7. The change of salt accumulation as a result of irrigation ............................................ 173.6. Table 8. Water management of the soil, irrigation method, water norm, connection between the rate and frequency of dosaging ................................................................................................................. 184.1. Figure 8. Dynamic water need and soil moisture (maize) .......................................................... 214.2. Figure 9. The impact of fertilisation on the water need (ET) and specific water need (Q) of sugarbeet(Ruzsányi, 1990) ................................................................................................................. 214.3. Figure 10. Correlation between the daily mean temperature and the evapotranspiration of wheat in the middle section of ontogenesis (Ruzsányi, 1985) ............................................................................... 225.1. Figure 11. Outline of the decision support module based on numerical modelling of a computerised irrigation control system .................................................................................................................... 245.2. Figure 12. Standard view of the logistic trend function describing plant growth ...................... 255.3. Figure 13. Main elements of the water balance of the plant population ..................................... 265.4. Figure 14. User interface of irrigation decision support system ................................................. 287.1. Figure 15. The effect of irrigation on fertilisation ...................................................................... 327.2. Figure 16. Crop year x fertilisation x irrigation effects (Nagy, 2002) ........................................ 348.1. Figure 17. Daily water use of potato during the growing season ............................................... 358.2. Figure 18. Potato rooting depth(Author's note: 1” (inch) = 2.54 cm) ......................................... 378.3. Table 10. Soil texture-based estimation of total available water and net water amounts per irrigation event during the potato growing season(Modified fromEfetha, 2011) .............................................. 378.4. Figure 19. Generalized soil water release curves for different soil types ................................... 388.5. Figure 20. Plant growth and soil moisture model (determinate, mid-season potato variety) ..... 398.6. Figure 21. Soil Moisture and Physiological Disorders in Potato ................................................ 408.7. Figure 21. Criteria for ranking the suitability of irrigation methods in potato production ......... 449.1. Figure 22. Daily water use of sugarbeet during the growing season .......................................... 479.2. Figure 23. Percent water extraction of sugarbeet in the top 120 cm of a soil profile having adequate water available (Yonts and Palm, 2008) ............................................................................................ 499.3. Table 12. Soil texture-based estimation of total available water and net water amounts per irrigation event during the sugarbeet growing season (Source: own calculation based on data of Yonts and Palm, 2008) .................................................................................................................................................. 509.4. Figure 24. Water movement in the 30 cm soil profile: sprinkler irrigation is applied after planting(Yonts and Palm, 2008) ......................................................................................................... 529.5. Figure 25. Water movement in the 30 cm soil profile: pre-plant sprinkler irrigation (Yonts and Palm, 2008) .................................................................................................................................................. 529.6. Figure 26. Effect of Sprinkler Device Placement on Water Application (location above ground: 1.8 m, 12 m wetted diameter and application time: 22 minutes) .................................................................. 549.7. Figure 27. Effect of Sprinkler Device Placement on Water Application (location above ground: 1.8 m,


Irrigated Farming

6 m wetted diameter and application time: 11 minutes) .................................................................... 549.8. Figure 28. Effect of Sprinkler Device Placement on Water Application (location above ground: 0.9 m, 6 m wetted diameter and application time: 8 minutes) ...................................................................... 5510.1. Figure 29. Seasonal water-use pattern of alfalfa ....................................................................... 5810.2. Figure 30. Alfalfa managed root zone for irrigation ................................................................. 6010.3. Table 17. Water management impact on diseases (Source: modified from Alfalfa Production Handbook, C-683, 1998) ................................................................................................................... 6611.1. Figure 31. Daily water use of greenpea during the growing season (Modified from Efetha, 2011) ............................................................................................................................................................ 6711.2. Figure 32. Greenpea root zone .................................................................................................. 6911.3. Table 18. Soil texture-based estimation of total available water and net water amounts per irrigation event during the greenpea growing season (Modified from Efetha, 2011) ....................................... 6911.4. Figure 33. Sweet corn rooting depth ......................................................................................... 7211.5. Table 19. Estimated daily cropwater use of sweet corn (Source: Fritz et al., 2010) ................. 7312.1. Figure 34. Water use of corn during the growing season .......................................................... 7512.2. Figure 35. Effect of plant population (plants/area) on corn leaf area index (LAI) ................... 7612.3. Figure 36. Seasonal water use of different corn maturities ...................................................... 7712.4. Figure 21. Average monthly PET and rainfall values during the corn growing season (Debrecen, 1980-2010) ......................................................................................................................................... 7812.5. Figure 22. Root zone soil water extraction and plant root development patterns .................... 7912.6. Figure 37. Formation of „milk layer” on maize kernel ............................................................. 8113.1. Figure 38. General pattern of growth and water use for soybeans ........................................... 8613.2. Figure39. Soybean root nodules ............................................................................................... 8713.3. Figure 40. Effect of wilting on soybean yields during reproductive growth stages ................. 8813.4. Figure 41. Effect of water stress on soybean yields at various growth stages .......................... 8814.1. Figure 42. Water balance and rooting zone of lowland rice ..................................................... 9614.2. Figure 43. Irrigated areas (A) and volumes of irrigation water used (B) in the world, in Asia, and in rice production ................................................................................................................................... 9714.3. Table 25. Total seasonal water input and daily seepage and percolation rates from lowland rice fields with continuously ponded water conditions >(Source: modified from Bouman et al., 2007) ........... 9814.4. Figure 44. Multiple Inlet Rice Irrigation. Contour of straight leeves ..................................... 10114.5. Figure 45. Field water tube for monitoring the depth of standing water in AWD .................. 10314.6. Figure 46. Yield responses to water availability and soil condition in different rice production systems(Source: Slaton (ed), 2006) ................................................................................................. 10515.1. Figure 47. Development of cotton rooting system ................................................................. 10815.2. Table 27. Soil texture-based estimation of total available water and net water amounts per irrigation event during the cotton growing season .......................................................................................... 10915.3. Figure 48. Seasonal daily water use for cotton production .................................................... 11015.4. Figure 49. Surface drip irrigation configurations for cotton .................................................. 119


A táblázatok listája2.1. Table 1. Water content in the plant cells ....................................................................................... 72.2. Table 2. Water content of vegetable organs ................................................................................... 74.1. Table 9. Static water need of crops (Ruzsányi L.) ...................................................................... 208.1. Table11. Water Deficit/Excess Effects during the Potato Growing Season (Curwen, 1994) ..... 4210.1. Table 13. Distribution of the amount of irrigation water in the growing season in the case of using surface and sprinkler irrigation methods (mm/ha) ............................................................................. 6110.2. Table 14. Alfalfa irrigation scheduling with calendar method .................................................. 6310.3. Table 15. Suggested values of soil matric potential at which irrigations should be applied for alfalfa for different soil types (Orloff et al., 2003) ....................................................................................... 6410.4. Table 16. Evaluation of alfalfa irrigation methods (Source: own editing on the basis of Alam and Rogers, 2009) ..................................................................................................................................... 6512.1. Table 20. Multiple decade mean temperature (°C) and precipitation (mm) of the corn belt in the USA (Source: Bocz, 1992) ......................................................................................................................... 7713.1. Table 24. Irrigation recommendations for soybean to maintain profitability (Source: Whitaker, 2012) ............................................................................................................................................................ 9114.1. Table 26. Advantages and disadvantages with Multiple Inlet Rice Irrigation (Source: own editing on the basis of Slaton (ed), 2006) ......................................................................................................... 10115.1. Table 28. Cotton’s responses to differing degrees of water stress (Source: modified from Gibb et al., 2012) ................................................................................................................................................ 11015.2. Table 29. Benefits and risks of irrigation during cotton growing season (Source: Perry and Barnes (eds), 2012) ...................................................................................................................................... 11315.3. Table 30. Impact of irrigation practices on the crop environment (Source: own editing on the basis of Allen et al., 2012) ............................................................................................................................ 11815.4. Table 31. Advantages and disadvantages of center pivot systems (Source: own editing on the basis of Perry and Barnes (eds), 2012) ......................................................................................................... 120


Tárgymutató


1. fejezet - 1. INTERACTION BETWEEN WATER MANAGEMENT AND CROP PRODUCTION IN AGRICULTUREDespite the decrease in demography, the population increases by 75 million people each year. According to estimations, the world population will reach 8 billion people by 2025 (Figure 1).

1.1. ábra - Figure 1. Increase of the world population (Source: wikipedia.org)

Parallel with the increase of population, the size of resources per person decreases. Therefore, the food demand of the population can only be covered with higher productivity and more effective production. In the next two decades, the food production of developing countries has to increase by 70% in a way that the planned increase of agricultural water use does not exceed 14%.

71% of the Earth is covered with water, but only 2.5% of this amount is sweet water. 0.04% of the total water stock is suitable for human consumption (Figure 2). The regional distribution of this amount of water is inequal, more than three quarters can be found in the arctic ice caps.

1.2. ábra - Figure 2. Global distribution of the world’s water


1. INTERACTION BETWEEN WATER MANAGEMENT AND

CROP PRODUCTION IN AGRICULTURE

If we compare the world’s countries to each other, it can be seen that Brazil owns 17% of the world’s water stock. India – which has six times higher population – owns only 5% of water. In the 20th century, water consumption increased sixfold, with significant differences in each region. While the average water consumption is 200 litre in Europe (110 l/person in Hungary), it is 10-20 l per person per day in the area surrounding the Sahara. Areas endangered by water shortage include North China, Australia, North Africa, the Middle East and India.

Agriculture is the largest sector of sweet water use (71%) in the world, followed by the industry (20%) and the communal sector (9%) (Figure 4). These proportions vary in each continent. For example, in Europe and North America, the industry has the largest water use proportion (42-45%), while it is the agricultural sector which uses the most water in Africa and Asia (84-85%).

1.3. ábra - Figure 3. Water use in each sector




The extent of irrigation is around 10% in agricultural water use, while its impact on the environment is enormous in the case of improper technology. The negative impacts on the soil structure and secondary salinisation affect 10% of the irrigated areas (30 million hectares of the 225 million hectares of irrigated land).

At the turn of the millennium, the agricultural area which was equipped with infrastructure suitable for irrigation was 2 788 000 km2 globally. 68% of these areas are in Asia, 17% in America, 9% in Europe, 5% in Africa and 1% in Oceania. The largest contiguous irrigated areas can be found in North India and Pakistan alongside the Ganges and Indus rivers, in China in the Hai He, Huang He and Jangce basins, in Egypt and Sudan along the Nile, as well as in the USA in the Mississippi-Missouri basin and in one part of California. Smaller irrigated areas can be found in nearly any part of the world.

1.4. ábra - Figure 4. Irrigated areas in the world (thousand ha) (Source: commons.wkimedia.org)

The unsustainable water management and the outdated, low efficiency technologies cause enormous water contamination and groundwater stock reduction. Underground water stocks might get exhausted mainly in dry areas where irrigation uses the deeper layers of the soil. The most significant cereal producer countries in the world (India, China, USA, countries of the Arabian Peninsula) decrease the amount of underground water by more than 160 billion m3 each year which equals the yearly water output of two rivers of the size of Nile. In Saudi Arabia, 75% of the water need is obtained from the groundwater. According to predictions, the water stocks will get exhausted sooner than the oil fields in 40 years.

Despite the negative examples, the significance of agricultural water management is revaluated, because it has a




significant positive impact on the environment and the society in the case of a proper agricultural policy.

In the last 10-15 years, the quality-oriented market determines the existence of a given crop production or horticultural sector, as well as the existential conditions and efficiency of producers to an increasing extent. The main requirement of the market is that the producer should be able to provide a relatively large amount of homogeneous goods and to have a steady transport ability.

The automation of the processing industry is increasing which supposes raw material of steady quality and quantity. The products purchased by direct end users are sold through store chains to an increasing extent, the size and business policy of which determines the previously mentioned homogeneous quality and steady transport ability.

In dry farming, climate change causes significant yield fluctuation. In the last 10 years, it can be observed that the average 25-30% yield fluctuation was caused by the unpredictable precipitation supply.

In order to achieve the homogeneity of the produced commodity supply, but mainly the safety of yield, irrigation is the main production technological tool to be used.

Without irrigation, the production of several crops could become uncertain. These crops mostly cover the sowing seed and propagation material production, plantations (grape, fruit) and field vegetable production. Nowadays, irrigation is not only a profit increasing intervention, but also a factor which serves market competitiveness.

This latter function increased the requirements of irrigation:

1. The extent and scheduling of irrigation should not be set in accordance with average production habits, but on the basis of exact meteorological data and the specific water supply ability of the soil, in conformity with the water need of the given crop species in each phenological phase.

2. Irrigation is a costly operation, the energy cost is the most significant item in its cost structure and the proportion of this item increases constantly. In the technique of water conduction and irrigation, the reduction of energy needs, as well as the scheduling and water dose are of chief importance.

3. The significant proportion of irrigated areas have relatively high groundwater level in the first months of the vegetative period. This phenomenon poses a risk of drainage water especially under irrigated circumstances. For this reason, the technology of irrigation has to be established in a way that the plant should use up the applied water during its vegetative period and irrigation should not increase the autumn water stock of the soil, if possible.

The water use of the world is doubled every 20 years, thereby determining the living standards of humanity. The food demand of the dynamically growing population can be covered with more effective agricultural production (water- and energy-saving technologies) and also by reducing the rate of desertification which affects significant areas in Asia and Africa. Increasing the efficiency of irrigation water use is a primary aspect in the development of production. Nowadays, 17% of ploughlands are irrigated, but this is the area where more than 40% of total yield is produced in the world. In the future, the most important task in the irrigated areas of the world is to improve the efficiency of irrigation from the current 38% to 42%. This 4% of increase in efficiency could result in significant saving in irrigation water. It is an indispensable task to technically modernise the irrigation equipment, to modify the proportions of irrigation methods (reducing the proportion of flooding irrigation, and increasing the share of microirrigation and underground irrigation).

Water allocations for the strategically important food production produced by irrigation:

1. Accepting the fact that there is no single solution for maintaining food security when water is scarce. All sources of water (rainwater, canal water, groundwater and wastewater) are important. They can all be developed under the right set of conditions, and additional storage capacity and recharge of groundwater resources form part of the long-term solution.

2. Finding the best options for specific conditions. Good and poor-quality land can be used for the production of food crops and other commodities, and the best combination of land, crop and water is site-specific but not ignore the inherent productivity of natural ecosystems.




3. Realizing that the ulink between irrigated agriculture and rural development is not always straightforward, rural development may be better served by investments in sectors other than irrigation.

4. Adopting natural resource based policies and institutions that encourage the integration of crop and resource management in order to identify the best location-specific options.

5. Facilitating and supporting actively the development of improved varieties as part of the solution for future food security.

6. Supporting actively the application of seasonal climate predictions in order to create the best combination of crop and resource management for the anticipated climate conditions.

7. Investing in irrigation modernization as an ongoing process, while recognizing each system’s specific comparative advantages. The aim of modernization should be to make the water delivery system and its management flexible enough to take full advantage of new technologies and crop varieties.


2. fejezet - 2. WATER BALANCE OF PLANTS, WATER DEMAND OF PLANTSWater is one of the most important elements of crops’ vital processes. Its natural resource is atmospheric precipitation: rain, snow and also dew to a smaller extent. Optimal water supply is the requirement of the undisturbed vital processes of crops. It has a determinant effect on the plant population, on the incorporation of dry matter and eventually on yield. Furthermore, water supply affects the microclimate of the plant population and determines the strategy and method of the actual production technological intervention.

Plant organisms demand the continuous presence of water; therefore, the water storage ability of soil has great significance in plants’ lives. Plants are able directly take up one part of the water stored in the soil; therefore, the moisture content of the soil has a direct impact on the vital processes of plants.

Water is of vital importance for plants because

• it is one of the main constituents of the vegetable organism;

• the nutrients in the soil are dissolved in water when utilised by plants;

• during photosynthesis, water provides the hydrogen necessary for the synthesis of organic matter

• a significant part of the energy of sunlight is spent on evaporation, which makes it possible the circulation of water in plants, thereby transporting the nutrients to the assimilating organs.

The water stored in the soil also has an indirect effect on plant life, as it has an impact on the microorganisms decomposing the vegetable and animal remnants; therefore, it is a determinant element of soil life. These organisms break down organic substances to their components; therefore, they make nitrogen and other mineral substance directly available for crops.

Plants contain large amounts of water partly in the cells and partly in the vascular bundles (Table 1.).

2.1. táblázat - Table 1. Water content in the plant cells

Cell component Water content %

cytoplasm 55-89

cell organelles 50

cell wall 50

Depending on the given phenophase, the water content of the green vegetable parts is between 60-95%. The maximum value is reached during flowering, while the minimum is reached during ripening (Table 2.).

2.2. táblázat - Table 2. Water content of vegetable organs

Water content %

grain yield (stored) 10-14

pulpy yield 80-95%


2. WATER BALANCE OF PLANTS, WATER DEMAND OF

PLANTS

leaf xerophyton 50-60

leaf mesophyton 80-90

The amount of water at the time of ripening is significantly lower in the case of the total water use of the plant as plants replenish the water loss resulting from constant evaporation from continuous water uptake. The nutrients solved in the water taken up this way make plant life and growth possible. Therefore, yield depends on the amount of water available for the plant and the accessed nutrients, as well as the intensity of transpiration. In order for the soil solution to enter the plant, its salt concentration always has to be lower than that of the fluid in the root hairs. If the concentration of the solution in the soil increases (either due to the high salt content or the low water content of the soil), water uptake decreases or even stops. The plant, which continues to evaporate starts to wither; if this conditions becomes constant, the plant will perish. The soil has to have a minimum water content in order to provide the undisturbed development of the vegetation. The minimum water content value increases as a function of the salt content of the soil.

The majority of water taken up from the soil leaves the system by means of plan transpiration. Transpiration is mainly affected by light and heat. The amount of evaporation water related to 1 m2 leaf area in an hour under various circumstances is as follows:

in darkness 3 grams

in shade 8 grams

in sunlight 65 grams

During the examination of the water consumption of plants, it is possible to determine the amount of evaporated water (/) that is needed in order for plants to be able to produce 1 kg dry matter during the growing season. This value is called transpiration coefficient or relative water consumption (Table 3.).

2.1. ábra - Table 3. Transpiration coefficient of various plants

In temperate climate 400-600 kg water is needed to produce 1 kg dry matter, depending on the production technology and the genotype. This amount significantly differs from the water content of the plant. For example, maize contains 75% water; therefore, 4 kg maize contains 1 kg dry matter and 4 kg water. On average, maize evaporates 300 kg water to produce 1 kg dry matter. Therefore, plant development needs 300/3 = 100 times as much water as what is contained by the plant.

The water use of plants is determined by climatic and physiological factors. Of climatic factors, light, temperature, air pressure and moisture have the strongest impact; of physiological factors, crop species and the shape and size of the leaf area determine water consumption the most. The impacts of these factors are additive, i.e. they determine water consumption together. Based on these factors, it is possible to estimate the water consumption for an entire growing season or a shorter period, e.g. a given month or phenological phase.

While the transpiration coefficient mainly has a theoretical significance (it can be used in practice less), the absolute water consumption provides a practically usable value for irrigation.

The development of plants does not have a steady rate, but it has outbreaks in certain development phases (e.g. vegetative phase, tasseling). Also, the extent of water consumption is changing in accordance with the uneven development rate of the plant. It is difficult to determine the continuous, exact water consumption of plants in the crop production space, but the values obtained in the lysimeters and microplots can be used in practice with proper care. The used water amount is expressed in m3 or mm, related to a unit area (m2, hectare) and it is


2. WATER BALANCE OF PLANTS, WATER DEMAND OF

PLANTSdetermined together with the water evaporated from the soil surface (Table 4.).

2.2. ábra - Table 4. Water consumption of the main irrigated plants

The necessary water amount increases in the case of a warmer climate. For example, water consumption increases by 30-50% to the south of the 45th parallel and the values shown in the table are doubled to the south of the 40th parallel.

The amount of water needed for a unit yield (or biomass) is expressed by the water use efficiency (WUE).

The index can also be used for grain yield, while the amount of water used by the plants can also refer to the precipitation during the growing season (or other periods) and the value of actual evapotranspiration. Accordingly, there are rather different WUE values in the specialised literature. The inverse use of WUE also became widespread, providing a productivity index, which expresses the quantity of dry matter or grain yield related to a unit of precipitation, irrigation water or evapotranspiration (Figure 5.).

2.3. ábra - Figure 5. Daily course of water utilisation (Source: Pethő, 1993)


3. fejezet - 3. EFFECT OF IRRIGATION ON THE SOIL AND PLANTSThe basic aim of irrigation is to provide optimum moisture for plants and to facilitate absorption by mobilising plant nutrients. The environmental friendly irrigation can be used if all factors affecting the successfulness of irrigation are taken into consideration. The joint effect of these factors are considered to be a complex system in which all fertilisation, cultivation and crop protection interventions are planned at the most optimal level.

Soil, as the basis of crop production affects the method of irrigation and its efficiency by means of its characteristics, physical, chemical and biological features. The soil suffers deep physical, chemical and biological changes as a result of irrigation, more specifically, large irrigation water doses. Consequently, soil productivity may change dramatically. This change could be favourable or even permanently favourable as a result of irrigations performed in an environmental friendly way. The favourable impact can simply be explained by the fact that high yields do not only represent the increased weight of above-ground parts of the plants, but also that of the root mass that is left in the soil. If proper agro technical and fertilisation methods are used, this residue could contribute to the increased productivity of the soil. In some cases, the improvement of soil productivity as a result of irrigation is so significant that irrigation is used directly as a soil improvement method.

The non-rationally planned irrigation induces the opposite processes in soil productivity. The improperly performed irrigation, the neglecting of natural endowments (mainly edaphic factors) and the non-satisfactory technical and agronomical conditions of irrigation (too high irrigation water dose, inadequate drainage, wrong cultivation, non-satisfactory nutrient supply, etc.) could lead to the reduced productivity of irrigated soils which is sometimes so severe that the irrigated area has to be withdrawn from cultivation.

During water replenishment, getting to know the soil characteristics is a significant aspect. Also, it is very important to examine the impact of irrigation on soil characteristics. The conditions of successful irrigation crop production can be established if soil characteristics are learned before or during irrigation and consistent soil monitoring is provided.

The interaction of the soil and irrigation is a rather manifold and complex process. Irrigation water, soil, the produced plants, as well as the groundwater level and its chemical composition play important role in this effect.

Irrigation significantly affects the water content of the soil, the water supply of plants and the nutrient uptake. This effect is usually favourable, because biomass production increases in the irrigated areas and higher yields can be harvested. The indirect impact of irrigation is a much more complicated and complex process, as it gradually changes the physical, chemical and biological characteristics of the soil, thereby acting on the soil formation processes. As a result of the process, not only the genetic nature of the soil, but, as a consequence of this, also the productivity of soil could change. These changes could have two directions: there can be a change during which soil productivity increases, while it is often the opposite process that happens. The two processes are in close correlation with each other as they go on parallel with each other. The changes which will affect soil fertility sooner or later as an indirect effect develop even as a direct impact of irrigation. At the same time, it can also be established that one has to count with the direct influence of irrigation during each new irrigation dose on the changed soils. For this reason, it is worth examining these two impacts always from the aspect of how they act on each other and as a unity.

In order to get to know these processes under specific circumstances, it is important to get to know the regularities of the movement of water getting into the soil and those of its interaction with soil, as well as the physical, chemical and physicochemical processes which go on between the soil and the irrigation water. This knowledge contributes to gathering information about the irrigation water to be applied, the quality of water and other aspects. Furthermore, it is also important to know these aspects because they are the basis of reversing the process of the reduction of soil productivity during irrigation; therefore, they are necessary in making productivity increase constantly.

Physical and water management characteristics of soil and their connection with irrigation.


3. EFFECT OF IRRIGATION ON THE SOIL AND PLANTS

Of the soil factors directly affecting the implementation of irrigation, the physical and water management characteristics of the soil have to be mentioned in the first place. These factors strongly affect the method of implementing irrigation, the doses and norms of irrigation, as well as its frequency and the selection of the irrigation method.

As a result of irrigation, soil gaps and pores of different diameter – that are usually filled with air when they are dry – get more or less saturated. The water penetrates the capillary space of the pores, as well as the larger air spaces between the pores as a result of the gravitational force. As a consequence of gravitational and capillary forces, plant roots take up and utilise the moving water. While practically all of the capillary water can be used by plant roots, the majority of gravitational water gets into the groundwater through cracks and is lost for the roots if they cannot reach into the groundwater zone. If the diameter of the fine pores in the soil is especially small (a few microns), water either cannot squeeze out the air from these pores at all or if the pores can be saturated with water, water will be strongly bound to them, making it impossible for plants to utilise it. Due to the heavy mechanical composition and high wilting point of the clayey and alkaline soils that are frequent in the Carpathian basin, the interval where the soil has enough so-called available water to not to be over-saturated with water and still have air for the roots and soil microbes is rather small.

In order to get to know the impacts, it is necessary to distinguish the water forms, which are bound in the soil by different forces.

Bound water is the part of soil moisture that is fixed on the surface of soil particles by adsorptive surface forces in the form of a thin layer. The binding of the water layer, which are in connection directly with the surface of the soil particles, is the strongest. As the distance from the surface of the soil particle increases, any further water layers are bound with decreasing force. The total surface of the soil particles, and, therefore, the extent of power working on the surface all depend on the particle and mechanical composition of soil particles. The finer the soil’s mechanical composition is, the larger the total are of soil particles is; therefore, the total quantity of bound water is also higher. Therefore, the percentage quantity of the strongly bound water on clay soils is multiple times higher than that of sandy soils.

Free water. The water, which penetrates the soil pores, maintains the balance with the capillary force, which is active in the pores; the more narrow the diameter of the capillary, the higher the capillary force is; accordingly, the smaller the soil pore capillary diameter is, the lower the mobility of the water is. The water that is not capillary mobile is located in the pores with the finest (< 1 micron) diameter. The capillary bound and mobile water is located in pores whose diameter is larger. In the rougher pores among the soil particles, the water maintains balance with the gravitational force; therefore, this rather mobile water is called gravitational water.

The plant is able to take up only a certain part of soil moisture. For this reason, the moisture in the soil can basically be classified into two groups from the aspect of plants:

• water not accessible for plants, wilting point (WP),

• water accessible for plants, available water (AW)

Wilting point (WP). The amount of water that is so intensively bound by the soil that plant roots are unable to utilise it can be characterised by the wilting point. The amount of this water is typical in the case of each soil type and it mainly depends on the soil structure and its mechanical composition. The amount of water below the wilting point cannot be accessed by the plant and if the soil does not contain moisture above this point, physiological withering starts. This value is of significant importance from the aspect of irrigation and it constitutes one of the initial bases during the calculation of the irrigation water doses to be applied. According to Hungarian examinations, this value equals four times the hygroscopic water stock of the soil, except for alkaline soils, because the wilting point is still significantly higher than the calculated value.

Available water (AW).If the soil dried out to the wilting point is watered under natural circumstances, the water will gradually infiltrate into the deeper regions while moistening the upper layers. The moisture content, which the soil is able to retain against gravitation under natural circumstances, is called field capacity. If field capacity is calculated for e.g. 100 ml soil and expressed in volume percent, then the calculated amount will be the necessary amount of water needed for the moistening of the 10 cm soil layer to its field capacity, expressed in mm. For example, if the field capacity of a soil is 19 % vol, then 19 mm water is needed for the moistening of the upper 10 cm of the soil.

If the soil is not dried out to its wilting point, the maximum irrigation doses to be set are equal to the difference



between the given moisture content and the field capacity. Above the field capacity, the soil is not able to bind water or it can only bind water temporarily; therefore, the amount of water applied above this capacity will not increase the moisture content of the upper layers, but it will deepen the leak, or, as a result of over-irrigation, puddles and water patches will be formed on the surface of the soil. Furthermore, the resulting airless conditions could also lead to the damaging of the plant population.

While the wilting point and the field capacity of the soil determine the irrigation water to be applied (its value depends on the given genotype), the water permeability and water conduction ability provides information about the method and speed of dosaging.

The water permeability and water conduction ability of the soil show how fast a given soil is able to conduct and receive water that gets on its surface.

Usually, the value of water conduction ability is determined in the field (on the spot) with two methods. The so-called framework soaking method gives a comprehensive value of the water conduction ability of the whole soil profile. It is simple to implement this method. The soil surface is covered with water in a regularly limited area and the speed of infiltration is measured in mm/min.

On soils whose layers of different depths have different water management characteristics, the so-called piped method is used. In such cases, the soil level which has the worst water conduction ability necessarily determines the water conduction ability of the whole profile. Therefore, if there is a more clayey layer of heavier mechanical composition under a loose brown forest soil relatively not too deep, then the water conduction ability of the whole soil profile will be determined by the water management characteristics of this layer.

At first glance, the water conduction ability of the soil depends on its mechanical composition and structure, or, in other cases, its pore characteristics, which determine its leakage profile (Figure 6.).

3.1. ábra - Figure 6. Leakage profiles of soils of various mechanical composition

The leakage profiles perfectly show that water infiltrates into sandy soils faster and the same amount of water moistens the soil in a smaller width but to a larger depth. The heavier the mechanical composition of soils is or the worse their structure is, the slower water infiltrates into them and the smaller the depth of leakage is, while the same amount of irrigation water moistens the soil to a smaller depth but in a larger width. It can be clearly seen in the figure that the depth of leakage is smaller on adobe soils, while its width is larger than on sandy soils. Furthermore, this phenomenon is even more obvious if one takes a look at clay soils. It follows from this that larger amounts of irrigation water and faster irrigation water dosing are needed on soils which have lighter mechanical composition. The heavier the mechanical composition of soils is, the slower one should dose the irrigation water and the smaller water jet should be used. The water conduction ability also has to be considered during the establishment of the technical equipment of the plots to be irrigated.

It can be established that wilting point, moisture content and field capacity expressed in % vol determine the amount of irrigation water to be applied and the extent of leakage, while the water conduction ability of the soil provides indispensable data for the equipment of the irrigation system and the implementation of irrigation itself. During these establishments, it was assumed that the water management characteristics of the various soil



levels are nearly identical, i.e., there is no layer in the soil profile which is more compacted, has worse water conduction ability and less favourable physical characteristics. As regards the majority of irrigated soils, this characteristic is not present, as there is a so-called level B at a certain depth under the surface, a compacted layer with poor physical and chemical characteristics which inhibits the infiltration of water in the soil profile and the movement of precipitation and irrigation water from above, as well as that of the moisture from the groundwater towards the upper layer. On these soils, only the level A, the so-called leaching level can be considered in terms of irrigation, a layer that is situated above the accumulation level, as the soil can accept and store only the amount of irrigation water that it retains to the extent that is in accordance with the field capacity of the upper leaching level. Further irrigation water doses do not increase the leakage depth, but there will be surface water patches if the upper level is over-irrigated.

The impact of irrigation on soil productivity can be classified into two groups:

• favourable impacts,

• unfavourable impacts.

- favourable impacts,

- unfavourable impacts.

Favourable impacts

The favourable impacts mainly affect the water management of the soil.

• Water replenishment during the growing season. The climate of Hungary and mainly the Great Plain is continental in one part of the year. As a result, summers are hot and the distribution of precipitation is inconstant. There are frequent shorter or longer period when the water stock of the upper layers of the soil gets used up and decreases to the wilting point. In these drought periods, the water supply of plants is unfavourable which is also expressed in yields. Therefore, if it is possible to provide water to the upper soil layers, i.e., the active root zone in the drought periods, the cause of yield decrease can be terminated.

In order to plan water supply, one has to know the water management characteristics of the soil, as well as its actual water content and the distribution of this water content in the soil profile.

• The improvement of nutrient management.The change, which occurs in the nutrient management of the soil also has to be classified among the favourable impacts of irrigation, as this process facilitates the extraction of the majority of nutrients and the amount of nutrients also increase as a result of active biological processes. All these phenomena can be explained by the fact that the favourable moisture condition contributes to the biological activity and increases the extraction of the mineral forms of nutrients from compounds that are more difficult to dissolve. The faster and more intense uptake of nutrients and easily soluble nutrients by plants is in close correlation with this phenomenon, since the nutrient uptake of plants increases if the necessary amount of water is present.

• Soil protection effect. The soil protection effect is also an important favourable impact and it is elicited by a low dose of water applied in the form of sprinkler irrigation in sandy areas. In dry and windy periods, soil degradation on sandy soils causes severe damages, but these phenomena can be totally terminated by applying small irrigation water doses (approx. 5 mm).

Unfavourable impacts

Unfortunately, the harmful impacts of irrigation on the soil are also significant and their extent decreases or totally defeats the favourable effect in many cases. The significance of these harmful impacts is increased by the fact that the favourable impacts are present only in years when precipitation is performed (taking production years as a basis), while the majority of harmful impacts last several years. The elimination of such permanent harmful effects has significant costs and cannot always be performed perfectly.

Therefore, the successfulness of irrigation can be improved mainly by eliminating these harmful environmental impacts from the aspect of the soil and also by predicting the probability of their occurrence, because the knowledge of their conditions provides a way to avoid the adverse phenomena.



Of the harmful effects, the following are necessary to be emphasised as impacts which occur frequently and on larger areas: structural degradation, the change of nutrient management, salinification, increased salt content, increased waterlogging.

• Structural degradation. This impact is developed as a result of the physical effect of irrigation water, including the erosion damages occurring as a consequence of irrigation. The flooding irrigation, drip irrigation, soaking irrigation and sprinkler irrigation methods all relocate the structural elements of the soil. The usually dry and warmed up soil aggregates burst and disintegrate into small pieces as a result of water. The water transports these tiny parts more easily. This phenomenon is also coupled with the physical impact of water drops, which results in the structural elements of the soaked soil surface becoming liquid and, after drying, cracked.

The only method of protection is providing the slow motion of water and the reduction of drop size and intensity in the case of sprinkler irrigation. As a matter of course, all these methods are not in line with other objectives of irrigation, which aim at applying the largest possible amount of water onto the surface during the shortest possible period.. For this reason, one has to identify the middle course, which satisfied both needs the best way while taking the conditions of economicalness into consideration.

• Changing the nutrient management. During the listing of the favourable impacts of irrigation, mention was made of the better extraction and uptake of nutrients. It follows from this that the harvesting of the irrigated plant withdraws nutrients from the soil as if it had not even been irrigated; irrigated plants extract more nutrients from the soil. However, it is also true that they provide higher yields, which make up for this impact.

However, the nutrient loss that infiltrates into the groundwater as a result of leaching will not be recovered by any means. A certain part of the mobile nutrients, which were extracted as a result of the more favourable moisture conditions will be lost for plants if the amount of irrigation water is so high that the moistened layer is connected with the capillary zone of groundwater.

A similar case occurs also if the moistening does not reach the groundwater or the layers affected by the groundwater but it washes the nutrients into soil layers that the roots of the plant do not penetrate.

In both cases, the leached nutrients are lost for the produced plants or those that are planned to be produced later.

Although this amount of nutrients is not as significant in comparison with the total nutrient content of the soil as it used to be believed in the past, but it still is not negligible, since it affects the easily soluble stock.

For this reason, the irrigation water doses have to be selected in a way that leaching should not occur. However, this need is in line with the aim to utilise irrigation water as efficiently as possible.

The other requirement which follows from the above mentioned fact is that more fertilisers have to be used in irrigated areas in order to fill up and increase the nutrient stock taken up by plants and reduced by leaching.

• Salinification and the increase of salt content. These impacts occur as a result of irrigation if high salt content and sodium containing water acts on the subsoil. This could happen if the quality of irrigation water is not satisfactory, but also if the irrigation water elevates the groundwater level and elicits salinification or the accumulation of salts in the soil.

The salinification that occurs as a result of irrigation does not only depend on the quality of irrigation water, but also the soil characteristics.

Groundwater circumstances

Similarly, attention must be paid to the groundwater conditions, as they can greatly affect the success of irrigation and lead to harmful effects.

The groundwater of irrigated areas or those, which are planned to be irrigated, can mainly be evaluated on the basis of the groundwater depthand secondarily the quality of groundwater. If the groundwater is close to the surface, special care must be taken about selecting the method of irrigation, as well as the size and frequency of irrigation water doses (Table 5–6).

Fluctuation of the groundwater level



In irrigated areas, the level of groundwater usually elevates to a smaller or greater extent. Possible reasons include:

• the water infiltrating from the channels move both downwards and laterally to reach the groundwater level,

• the high irrigation water norms, the frequent irrigation and the high amount of precipitation after irrigation result in the fact that the water infiltrating into the soil reaches and floods the groundwater,

• the irrigation water fills up the pores of the surface soil layers, thereby reducing the evaporation of groundwater through the soil surface.

3.2. ábra - Table 5. Water management of the soil, irrigation method, water norm, connection between the rate and frequency of dosaging (Filep)

3.3. ábra - Table 6. Classification of water types from the aspects of usability for irrigation purposes (Darab and Ferenc)



Critical groundwater level

In the case of continuous irrigation, the elevation of the groundwater level could be even 20-30 cm per year, which eventually means the entering of groundwater into critical depths. In the case of groundwater at critical depths, the capillary zone could contribute to the surface evaporation, thereby salinisating the soil layers by concentrating the salts dissolved in the groundwater and eliciting salt accumulation.

The critical depth is not independent of the salt content of the groundwater, because the more salt the groundwater contains, the larger depth it can emerge from in order to impose its harmful effect. However, the critical depth is not independent of the soil characteristics either, as these are the factors, which determine the elevation conditions and the extent of evaporation.

During the assessment of groundwater conditions, the main question is whether the distance between the highest level of groundwater and the surface reaches 4 m. If the groundwater level is closer to the surface, then the groundwater above 1 m has to be strictly separated, as the area must not be recommended for irrigation and the ongoing irrigation activities have to be stopped (Table 7.).

3.4. ábra - Table 7. Critical groundwater depth and the salt content of the groundwater (Kovda)



The elimination and prevention of harmful effects attributed to the elevation of the groundwater level have to be taken special care about. It is important to monitor the changes of groundwater level and if it increases each year, the irrigation water norms have to be reduces or the irrigation has to be stopped in extreme cases.

The consequences of improper irrigation and the aspects of protection against harmful effects

Secondary salinification. Both the low quality irrigation water and the high salt content groundwater elicit salt accumulation and salinisation in the soil. This phenomenon is especially harmful and quickly occurring if sodium cation and carbonate – hydrogen-carbonate anion are dominant in the salt content of water.

Therefore, the favourable physical and chemical characteristics of soils originally belonging to the meadow or chernozem type degrade and their morphology, as well as their chemical and physical characteristics will resemble of those of alkaline soils. This phenomenon is called secondary salinification (Figure 7.).

Salt balance. Only the salt balances can provide totally accurate information about the nature of salt accumulation, as well as its tendency, its quantity and quality relations. These balances show the changes in water-soluble salt content accumulated at various levels of the soil based on the cumulation of the results of periodical soil analyses. If the salt balance is positive, salts are accumulated in the soil, but if it is negative, salts are being leached.

3.5. ábra - Figure 7. The change of salt accumulation as a result of irrigation

Waterlogging. Waterlogging, increased meadow, bog and marsh characters are significant forms of the harmful impacts of irrigation on the soil.

Basically, all of the above listed conditions are different stages of the same process and they develop as a result of a too long-lasting water cover or too wet circumstances.

As a result of the unsatisfactory levelling of the ground, water is collected in the depressions of the irrigated area



and they cover the soil for almost the entire year. In this case, reduction processes are becoming dominant and this phenomenon changes the soil dynamics fundamentally, from the degradation of the organic matter and the formation of new organic matter to the mobility of iron and manganese and the binding of nitrogen and phosphorus compounds. Since the reduced iron and sulphur compounds cause the intoxication of plants and the availability of nutrients significantly decreases, the soil productivity strongly decreases as well.

The elevation of groundwater level could have the same impact if the salt content of the soil is not high. It will lead to the increase of the salt content of the groundwater that is rich in dissolved salt and close to the surface, while small salt content, weakly mineralised waters close to the surface elicit the waterlogging of the soil and the increase of its meadow and then boggy character. If the water coverage is present during the whole year or the groundwater elevates to the surface, the soil becomes marshy. In this case, the organic matter getting onto the soil will not be mineralised, but it accumulated on the surface and creates a peaty, boggy layer.

As a matter of course, this phenomenon is coupled by the fact that the plant cover changes as a result of permanent water coverage or even only because of the excessive abundance of water. Mostly weeds that tolerate the constant water coverage will become dominant; therefore, sedge, reed, bulrush and other water plants proliferate and their organic matter significantly differ from that of plant populations preferring dry conditions. The appearance of plants which tolerate constant water cover indicate waterlogging and the increased meadow, bog and marsh characters, thereby making it possible to carry out timely prevention against them.

Protection can be performed with the levelling of the ground, the reduction of irrigation water norms, the suspending of irrigation and the reduction of the groundwater level that are also coupled by the aeration and drying out of the soil.

To summarise the irrigation-induced harmful changes, it has to be emphasised that they can only occur if there are mistakes in irrigation. These mistakes could result from both the quality of irrigation water and the improper choice of irrigation water norms.

Since all these factors can be altered, the harmful impacts can be avoided or eliminated.

If the water and soil conditions rule out irrigation in advance, the best solution is to stop irrigation and withdraw the area in question, because its operation cannot be economical and will lead to the total improductivity of the soil sooner or later.

Based on the above statements, the following soil-related aspects have to be effectuated in irrigation:

• During the selection of the irrigation plant area, the places whose soil conditions are not in line with the available irrigation water or the depth and composition of the groundwater is not adequate should be excluded.

• During the selection of the irrigation method, it is important to consider the terrain and the changes occurring during levelling, because the soil levels with unfavourable characteristics could come to the surface from under the trimmed soil layers. It is also important to consider the water management of the soil, i.e., the water intake and retention capability.

• During the determination of the irrigation water norms, the groundwater level also has to be considered in addition to the water intake and field capacity, taking care about avoiding its elevation to the critical depth.

• The irrigation water quality has to be evaluated in conformity with the soil. In addition to the original composition of the water, the chemical characteristics of the soil to be irrigated also have to be considered if there is a need for soil improvement.

• The chance of secondary salinification has to be prevented by improving both the irrigation water quality and the water conditions of the soil and by strictly conforming to properly selected irrigation norms.

• One has to fight against waterlogging and the increased meadow, bog and marsh characters by preventing constant water cover and the elevation of groundwater to the surface (Table 8.) .

3.6. ábra - Table 8. Water management of the soil, irrigation method, water norm, connection between the rate and frequency of dosaging


4. fejezet - 4. NECESSITY OF IRRIGATION, EFFICIENCY OF WATER USESeveral concepts have to be known in order to analyse the regularities of water management in the agricultural plot and to adapt them in practice. In order to determine the amount of water needed for the dry matter production of a given plant population, as well as the extent of water shortage, one has to know the regularities of the forces which act on the water cycle in the given artificial ecosystem. The agricultural plot can be distributed to several zones in which the plant population is middle layer between the soil and atmosphere that not only separates (static) the zones but also actively participates in the material and energy transport, stores and transforms assimilates and energy. In a given point of time, the condition and reaction of the plant population represent the impact of the atmosphere and the soil. In order to get to know the regularities of the water cycle, which is one of the most important material flows, one has to know the various quantity and quality characteristics.

The static water need represents the need of crops for the relative moisture content of the soil. This index is more about the air need of plants than their water need by determining how many percentages of the pore space of the soil should be filled up by water and how many percentages by air (Table 9.)

4.1. táblázat - Table 9. Static water need of crops (Ruzsányi L.)

Crop Water content in the % of pore volume

weather, barley 72-75

maize 67-70

sugarbeet 65-70

red clover 86-90

cabbage 88-90

tomato 74-75

alfalfa 78-80

The reduction of the oxygen supply of the soil leads to root suffocation. This is a frequent phenomenon on high plasticity soils in autumn-sown populations after quick snow melting early spring. Plants are not damaged by too much water, but too little air. If the stagnant water is not drained on time, the plant population becomes yellow and perishes in a few days. One of the main aims of rational cultivation of proper quality is to establish a structure which contributes to the aeration of the soil. The optimum static water need greatly depends on the physical type of the soil and the proportion of grain composition. For example, 70% relative moisture on high plasticity soils means a lot less accessible water than on mid plasticity soils. For this reason, it might happen that this moisture condition totally satisfies the air need of a certain plant in high plasticity soils but it is not able to cover its water need.

The dynamic water need is the water equivalent (mm/hour; mm/day) of the water vapour entering the atmosphere from the plant population and the temporal change of this water vapour in a soil moisture range where the plant does not suffer any damage. The dynamic water need is the change of plants’ water need during the growing season (from emergence to ripening) (Figure 8.).


4. NECESSITY OF IRRIGATION, EFFICIENCY OF

WATER USE4.1. ábra - Figure 8. Dynamic water need and soil moisture (maize)

If the growing season is shown on the horizontal axis in a system of coordinates and the water need is shown on the vertical axis, the dynamic water need is usually a single-peak curve. Based on the rise of the curve, the extension of the peak range, as well as the length of the section projected to the horizontal axis and its location, it is possible to estimate the plant’s proneness to drought in addition to its water need. If the steep range of the curve falls to the spring months and the peak period is short, the plant suffers from water shortage less often. If the rapid increase of water need also extends to the summer period and the peak of the curve falls to July-August, there is an increased risk of drought, resulting in yield reduction.

The specific water need is the ratio of water accessed by the plant and the production of the plant. The value of specific water need is reduced by fertilisation as long as the increase of production outweighs the increase of the amount of water used (Figure 9). The yield increasing effect of fertilisation is shown by an optimum curve, while the change of water need is parabolistic. The results of the examinations show that the increase of yield has a higher rate until applying a given fertiliser dose than the increase of water uptake and water need, depending on the production circumstances of each crop. Therefore, the utilisation of water taken up by plants improves as a result of irrigation and the value of specific water need decreases.

4.2. ábra - Figure 9. The impact of fertilisation on the water need (ET) and specific water need (Q) of sugarbeet(Ruzsányi, 1990)



WATER USE

The impact of successful protection against weeds also reduces water need. The plant population that is free of pathogens and pests utilises the available water stock better. The evaporation of the soil surface greatly depends on the method of cultivation and the number of operations.

Of the biological factors, the characteristics of species and varieties affect the water need the most. There is a close correlation between the length of the growing season and the water need. Accordingly, field crops can be classified the following way:

• low water need plants (pea, poppy, etc. ),

• average water need plants (potato, wheat, sunflower, soy, maize, etc.),

• high water need plants (sugarbeet, fodder beet, alfalfa, red clover, etc.)

In addition to water need, plants’ sensitivity to water and the active rooting depth are determinant characteristics from the aspect of production. Of shallow rooted plants, those that have short growing seasons have low water need, but are the most sensitive (pea, poppy etc.). More deeply rooted plants are able to survive dry periods without any precipitation (e.g. maize, sugarbeet, alfalfa, sunflower etc.).

In the period of the development of generative organs (flowering), the water need of plants and their sensitivity to water shortage is the highest.

Of the climatological factors, the amount of water evaporated by the plant population, the water need of the plant population depends on the amount of energy, the “energy hunger” of the layer of air. Based on the knowledge of the speed of energy flow, the possible evaporation can be determined in the given period of the growing season and the water need can be calculated.

Air temperature has both a direct and indirect impact on water need. The direct impact is the change of the intensity of the plant metabolism, while the indirect impact is the change of the relative humidity of air. The water need of plant populations increases with the increase of air temperature to a different extent in the case of each plant species. In accordance with the production site endowments, the given air temperature where water need does not increase any further can be determined for each plant. Further increase in temperature results in the decrease of water uptake and water loss and eventually the perishing of the plant. Water need is affected by even more factors: the mass of radiation, sunshine duration and the air turbulence. The increase of radiation, sunshine duration and air turbulence increase water need.

4.3. ábra - Figure 10. Correlation between the daily mean temperature and the evapotranspiration of wheat in the middle section of ontogenesis (Ruzsányi, 1985)



WATER USE


5. fejezet - 5. EVALUATION OF IRRIGATION DOSESDetermining irrigation water as accurately as possible is an increasingly topical question of crop production sectors, since the availability of water as an input resource is unbalanced and uncertain. The increasing yield level, the periodical extremities of climate and the limited character of the water base, as well as the constantly increasing irrigation costs necessitate the rationalisation of input use, which is a critical factor of economical production. Accordingly, the needs point beyond the determination of single irrigation doses of a certain plot, but the traditional methods based on empirical or statistical principles are not able to meet these requirements. In order to operate the automatic (precision) systems of large-scale plants in an economical way, decision support background is also needed in addition to the automatic sensory measurement and registration of soil moisture. There are various procedures available for the planning of the irrigation schedule, or, in a wider sense, the modelling of the water cycle of the soil-plant-climate system. These methods are usually deterministic models or model-submodel complexes whose input parameters use meteorological, agrometeorological or occasionally plant phenological measurements and observations, while the boundary conditions are soil, plant and plant phenological parameters. The outputs of these models are the water balance of the crop production space and other derived information (Figure 11.).

5.1. ábra - Figure 11. Outline of the decision support module based on numerical modelling of a computerised irrigation control system

In this case, the concept is to set up a complex water balance built on the estimated evaporation based on the wide range and precise measurements of meteorological parameters, as well as the detailed database of plant phenological and soil parameters and to provide up-to-date and operative information serving individual needs by involving further inputs.

Agrometeorological inputs

The range of agrometeorological information needed by the model is wider than the measurement programs of basic weather stations used for agricultural purposes. In addition to temperature (T), relative humidity (RH) and precipitation sum (p), the following parameters are needed for the calculations: global radiation (RG), radiation balance (also called as net radiation, Rn), wind speed (w) and the moisture content (θ) of a soil profile of a specific depth.


5. EVALUATION OF IRRIGATION DOSES

Calculation of the reference evaporation

There is a large number of available algorithms for the submodel performing the estimation of evaporation, there are lots of versatile methods referred to in international specialised literature. It also has to be noted that the various approaches and the differences between them in terms of geographical origin and climatological views are worth considering when choosing between them. Furthermore, the adaptation, validation and calibration of the used algorithms to local circumstances cannot be neglected either. The product of the submodel is the so-called reference evaporation, which is equal to the potential evaporation value measured on an idealised grass surface. Using the multiplication factor of the given plant population (crop coefficient, Kc), the evapotranspiration of any population can be produced, taking into consideration the differences arising from the species, variety, utilisation method, plant conditions, as well as the variability of production technology and production site. Altogether, the accuracy of evaporation estimation fundamentally determines the success of the accurate quantification of the water balance. The reason for this phenomenon is that the material and energy flow circumstances of the air space of plant populations are developed by relatively manifold and complicated processes which are often impossible to model at a population level; therefore, the temporal and spatial extension of the measured evaporation values are filled with errors.

Plant and soil parameters

The modelling of the water balance of the plant population as an ecosystem is actually the simulation of every involved significant exchange process related to the given period. These processes have a temporally changing nature, since the modelling task is usually not a single one, but it has to cover the whole growing season of the plant population and the entire development course of the vegetation. The boundary conditions needed for the modelling of growth can be classified in the following groups:

• limit values showing the length of the growing season (sowing, emergence, harvesting)

• the length of phenological phases (initial, development, middle and post phases)

• typical limit values of plant growth (plant height and root depth)

• values describing the effect of the agrotechnological operations affecting growth (e.g. the impact of reaping, pruning and tillage method on plant height)

From the aspect of growth dynamics, the cash crops produced in Hungary are rather different, as annual, biennial, perennial, spring- and autumn-sown populations call for the use of different, often total unique growth functions. Typically, the growth curve of plants is a logistic trend functions that refers to the development of both above- and below-ground vegetable parts. The curve shown in Figure 12 is the simplest example and can be used for the entire life cycle of annual, spring-sown populations or perennial woody plantations (e.g. fruit trees).

5.2. ábra - Figure 12. Standard view of the logistic trend function describing plant growth



The above-ground part of autumn-sown plants (e.g. certain cereals, rape) show a growth rate that can be described with transformed and combined functions, while the growth of the root system can still be characterised with the above described logistic trend. The other parameters of plant life functions are the plant evaporation coefficients (Kc) which change in each development phase. In each model, there can be one or even more coefficients, depending on how detailed they are, the latter of which distinguish the different phenophases and run separate calculations water use from the upper (evaporative) and deeper layers of the soil while they also deal with the impacts of any possible water stress.

The water use equivalent (p) is a further plant parameter and it serves the description of the availability of the water stock in the soil. By introducing this parameter, the model becomes able to calculate the present, but inaccessible amounts of water for each species, variety and utilisation type; therefore, this aspect can be considered subjective.

The simulation of plant growth dynamics and the water supply background of vital processes are based on several soil parameters. These parameters can be related to given geographical locations or plots, but due to the wider range of usability and even the mosaic regional character of soil conditions, the extendibility of the model even within the plot itself necessitates that there should be available data for several soil types and physical types. The most necessary information based on which the water management characteristics can be calculated are as follows:

• soil (physical) type

• Field Capacity (FC)

• Wilting Point (WP)

• optionally, the initial and/or constantly measured values of soil moisture (θ) if there is a possibility of measurements

Calculating the water balance of the root zone

In order to determine the doses of the necessary water replenishment, one has to know the amount of water that is missing from the respective soil profile. As a matter of course, this amount also depends on plant needs. Practically, this value is the “gross sum” of the individual water balance which could be zero or even positive, when there is no need for irrigation water.

The majority of the members in the balance cannot be measured in practice, they are physical quantities which can be estimated; therefore, during the establishment of the model, one has to take into consideration the appearance of errors arising from this fact. The basic principle could be the minimising of inaccuracy, as the total elimination of error is impossible under field circumstances.

Simplified for of the water balance:

Peff+I+CR=ETc+RO+DP,

Where:

Peff: effective precipitation sum

ETc: evapotranspiration of the crop stand

I: quantity of irrigation water

RO: surface runoff

CR: capillary elevation

DP: infiltration into deeper layers

5.3. ábra - Figure 13. Main elements of the water balance of the plant population



In addition to the main elements in the equation above, the simplified water balance scheme shown in Figure 14 also contains the evaporation from the soil surface and the transpiration of the soil surface not covered by the culture crop (but weeds) and is illustrates the two soil layers that can be distinguished from the aspect of the evaporation process. The water balance of the upper 10-30 cm layer (Z e) affected by evaporation greatly differs from the layer beneath which is determined by the penetration depth of the root system (Z r), while it also has an impact of the water balance conditions of the latter.

Since this simulation method was set up especially in order to utilise the advantages of process approach in irrigation decision support, it is self-explanatory to use the model in a recursive form. This means that balance is set up continuously in periodical (daily) steps; therefore, every given (ith) daily balance is built on the preceding (i-1th) daily value and also serves as the basis of the upcoming (i+1th) daily balance.

The amount of irrigation water needed for the whole (0) water balance can be expressed in a given day from equation (1), but since the aim of water replenishment is not this, but to provide optimum growth under economical circumstances, it is substituted by the concept of depletion (D):

Di=Di-1-(P-RO)i-Ii-CRi+ETc,i+DPi,

where the respective days (i, i-1) were indicated in subscript.

The guiding principle of calculating the actual irrigation water need is that the moisture stock of the soil in the profile that is accessible for the root system should not decrease below the amount of water which can be easily taken up by plants:

That is: Dr,i≥RAW,

Where RAW represents the readily available water.

If this happens, water stress occurs and the development is restricted either temporarily or permanently and will be followed by irreversible damage which could lead to yield decrease.

The correlation between the extent of water shortage and the amount of water to be applied mostly depends on the farming strategy, in other words, the aims set in relation to irrigation tasks. From the aspect of the system, it can be expected to give out the signal indicating the necessity of irrigation in any second, while it provides recommendation referring to the amount of water to be applied. This amount is the difference between the level of the readily available water and the actual water shortage. At the same time, farmers have to set their individual goal and adjust the system accordingly.

Technological corrections, meteorological model outputs

The raw model output is often difficult to interpret for its users; therefore, it is an important function of decision support systems to customize outputs, as well as to improve the practical usability and also to make it easier.



Figure 15 shows the simple user sample interface of an irrigation decision support model collective. In addition to the visualisation elements, this model enables users to specify a few technological parameters, too. Therefore, the system is able to consider the efficiency of the irrigation method and the equipment, the proportion of the soil surface moistened this way, the highest daily irrigation water to be applied which is determined by the capacity of equipment, as well as the individual irrigation-related goals and attitudes of the farmers (extensive, average or intensive).

The value of the information provided by similar systems can be further increased if they are provided to users with a so-called time advantage. The meteorological data, which serve as the basic parameters of the system can be extrapolated and predicted also with the help of modelling procedures. By the integration of model outputs (taking into consideration that the reliability of the meteorological model results significantly decrease outside the 0-72 hour time frame), it becomes possible to consider the meteorological conditions of the near future at a given level of uncertainty in addition to past and present data. Therefore, the planning of agrotechnics and the timing of interventions become easier and the risk is diminished.

5.4. ábra - Figure 14. User interface of irrigation decision support system


6. fejezet - 6. PRINCIPLES OF TILLAGE IN IRRIGATED FARMINGIrrigation is the replenishment of natural water supply, the prevention of water shortage which increases production risk and the covering of plant water need at the level that is reasonable from the farming point of view.

During irrigation crop production, soil is affected by loads in connection with regular moistening. According to Nyíri(1997), loading is especially harmful if the method and intensity of irrigation or the amount of irrigation water is not tailored to the given soil characteristics and the water intake ability of the soil is neglected.

Frequent soaking could lead to anaerobic conditions in the soil and its structure could deteriorate due to the mechanical impact of water. As a result of regular irrigation, the soil whose structure is damaged becomes more sensitive to physical loading. The silting of the soil surface, as well as the faster depositing and recompaction of the cultivated layer are frequent phenomena.

The mapping of irrigated soils and the compilation of soil expert’s opinions – regarding the water permeability and the water/air ratio of the soil – are great help in predicting the expected changes and impacts and in determining the necessary tasks.

During the establishment of the cultivation systems of irrigated crops, it is a primary aspect to increase the efficiency of artificial water replenishment and the reduction of soil degradation.

Tasks to be performed in order to reduce or prevent soil degradation:

• regular examinations are needed in order to detect mistakes on time,

• the cultivation mistakes which elicit or increase structural degradation, i.e., compaction, cloddiness, dustification and organic matter loss should be avoided.

• the necessary looseness until the depth of the root zone has to be established or preserved,

• organic matter preserving and water loss reducing cultivation should be used,

• the structure of the upper soil layer has to be spared outside of the growing season,

• it is important to establish and maintain conditions which make it possible for water to infiltrate into the soil as soon as possible (water intake) and to move within the profile in a fast and steady way (water conduction). The air supply of the soil and the plant roots also has to be provided.

The following aspects have to taken care to make sure that irrigation water gets into the soil:

• Water intake is improved by the soil condition, which protracts the silting and airless character of the soil.

• The (occasional and total) irrigation water dose and the intensity of irrigation have to be determined based on the soil characteristics and conditions.

• he irrigation water dose and the irrigation intensity have to be determined in a way that no stagnant water remains on the surface or in the root zone as the reduction of stress, which holds back plant development also results in the improvement of the applied irrigation water.

• The water and air cycle of the upper layer can be improved with row spacing loosening. The cultivation of row spacing can take place after irrigation and the drying of the soil in the initial development phase of plants which are sensitive to the closure of the surface and the air supply level of the root zone (e.g. maize).

The soil that became compacted as a result of irrigation and other physical loads can be prepared for the production of the upcoming plant – and another irrigation – with improvement and sparing cultivation. The sections of soil preparation is determined by the adaptation to circumstances.


6. PRINCIPLES OF TILLAGE IN IRRIGATED FARMING

Stubble stripping and treatment. The general aim of soil work is the same as in the case of non-irrigated circumstances. Special attention should be paid to reducing the moisture loss of the soil and the sparing of the soil structure. On irrigated soils, stripping performed with a tine should be preferred against disking. The partial coverage of the stripped surface could protract the water loss of the soil. When the drying of the soil is more important, stripping can be performed slightly deeper and one should aim at better mixing. Stronger weed and volunteer plant emergence should be expected; therefore, the mechanical treatment soil work cannot be neglected.

Crushing the residues of late harvested crops should be performed in one process if possible. The stem crushing may need extra activity, as larger mass is produced under irrigated circumstances, the stems have high moisture content and they are not ripened until harvesting.

Basic cultivation and finishing of the surface. Proper quality can be reached on the soil whose surface layers are properly managed with stripping and treatment if the following aspects are taken into consideration:

After early harvested previous crops, cultivation with a tine used as basic cultivation for late summer and autumn sown crops spares the soil. Flat disc dustifier is also a proper solution.

After previous crops harvested early to mid-summer, the soil improving moderately deep loosening is only recommended in the case of spring-sown crops if the layer to be loosened is dry. At the same time, the surface of the opened soil has to be levelled and closed. On plastic to highly plastic soils, regular use of deep loosening might become necessary.

Plough pan soil compaction could be avoided if the depth of ploughing is different than that of the preceding year. Ploughing should be carried out if the soil surface can be finished in one operation with a tool mounted on or after the plough.

Seedbed preparation and sowing. In the case of late summer and autumn sowing, less compaction damage, clods and dust are developed if seedbed preparation and sowing are performed in one operation. A similar solution can be recommended in the case of sowing cereals. The spring soil work of root crops depends on the quality of the autumn basic cultivation (the extent of surface finishing in the autumn). In order to spare the soil structure, multiple operation cultivation methods, as well as the use of tools smearing, kneading and dustifying the soil (e.g. traditional disc, smoother) should be avoided. After sowing, profiled surface has to be developed also in order to avoid silting.

Treatment of irrigated plants. The plant treatment should mostly focus on correcting the soil problems related to irrigation (silting, cracking, airless conditions) and weed control. It might also be necessary to apply substances which facilitate the nutrition and protection of plants, as well as the improvement of their conditions. The physical load of the production site soil can be reduced with using cultivation tracks.

The scheduling, method and intensity of irrigation, as well as the irrigation water dose have to be determined based on the given soil characteristics and conditions, while the water intake and proper aeration of the soil also have to be provided.

In order to facilitate the water in the soil profile to move steadily and to contribute to the proper air supply of the soil and the plant, the following aspects have to be paid attention to in accordance with:

• If the irrigation intensity is higher than the water intake of the soil, the soil layer is saturated with moisture to or close to its maximum field capacity (FCmax) as a result of irrigation.

• In the case of maximum or nearly maximum moisture saturation, the air capacity of the soil is reduced to the minimum.

• The unfavourable physiological effect of insufficient air supply could be further increased by the cold irrigation water.

• The unfavourable soil condition resulting from high moisture content lasts until the water/air ratio of the soil reaches 70/30 needed by plants or at least 80/20.

• The downward movement of gravitational water is quick and the airless soil conditions do not take long. The water permeability of the soil is good (100-300mm/h) or very good (300 mm/h). The air capacity of high water permeable soils is around the expected 30% or at least 20% in accordance with their natural water


6. PRINCIPLES OF TILLAGE IN IRRIGATED FARMING

storage ability.

• In the case of average (70-100 mm/h), poor (30-70 mm/h), or very poor (<30 mm/h) water permeability, the air supply of the soil may become insufficient. The airless character of such soils is not eliminated even when they reach their natural water storage capacity, because their air capacity is lower than 20%. After irrigation, the long period of airless conditions could lead to the ineffectiveness of irrigation and the damaging of the plant (switching to yellowish green colour). These phenomena can be avoided with deep cultivation, which increases the water permeability of the gravitational pore space and the soil, as well as the efficiency of irrigation in an indirect way. The necessary depth of cultivation is determined by the depth adversely compacted layers and the thickness of the layer to be soaked with irrigation.

Due to the irrigation during the vegetative period, the following aspects have to be paid attention to in order to restore the looseness and porosity of the more severely compacted soil:

• One should avoid the circumstances leading to compaction, i.e. the mechanical treading and cultivation of the wet soil.

• The upper soil (which usually has deteriorated structure) has to be ploughed under the surface.

• In accordance with the crop order, it is recommended to switch the basic cultivation procedures which improve the soil condition and spare its structure.

• The upper layer of the irrigated soil or the soil prepared for irrigation has to be maintained in a favourable (powdery) condition in order to prevent silting.

• During the planning of each operation, it has to be considered that the duration of effect of deep cultivation (deep loosening) is short on irrigated soils, taking one, or the maximum of two growing seasons.

As regards further tasks, their description is provided in the subsection “The cultivation systems and treatment of irrigated soils”.


7. fejezet - 7. PRINCIPLES OF FERTILISATION ON IRRIGATED FIELDSWater is a solvent in the dissolution of nutrients needed by plants and it takes part in the transport of salts taken up by plants as a vehicle. The majority of the nutrients taken up by plants are transported by the transpiration water flow to the various parts of the plant.

However, the nutrient flow through the absorbing root surface of the plant is basically independent of water uptake and depletion. If the concentration of the soil solution is high and the suction cells of the root are oversaturated, the further nutrient uptake greatly depends on the intensity of transpiration. For this reason, the maintenance of the available water content of the soil may greatly affect the uptake of the nutrients in the soil, as well as their transport, i.e., their efficiency with regard to the quantity and quality of yield. Subsequently, the quantity and quality of yield is primarily determined by the water and nutrient supply of plants at a given point of time, in addition to other factors. The efficiency of high nutrient concentration artificially established in the soil (with fertilisation) can be significantly improved with better water supply. The microbiological activity of the soil is also affected by proper water supply, which is in close correlation with the extraction of mineral nutrients. Fertiliser added to the soil can increase the activity of soil microorganisms under favourable soil moisture circumstances; therefore the mineralisation of organic matter is also improved.

The moisture content of the soil affects the effectiveness of fertilisers, the extraction of nutrients and their uptake by plants. However, findings regarding the correlation between the nutrient uptake of plants and the moisture content of the soil are different in several points.

Several experiments show that the reduction of soil moisture leads not only to slower plant growth, but also to slower nutrient uptake. Other experiments concluded that certain plants take up the nutrient also from dryer soils if a certain part of their roots is in the wet soil. The further examination of this topic is very important in order to determine the scheduling of irrigation, the irrigation water norm, as well as the method and depth of incorporating water into the soil for each plant and soil type. Each plant’s water and nutrient needs are different; therefore, they should be taken into consideration in the decision about the extent of irrigation and fertilisation. It is a general principle that better water supply can provide higher yield surplus mainly on soils that are rich in nutrients as the extent of nutrient use increases with water supply. For this reason, if the amount of fertiliser to be used is determined on the bases of the expected average yield, the reduction of yield quality can be stopped. Better water supply usually improves the efficiency of fertilisers, while favourable nutrient supply decreases the transpiration coefficient of plants.

However, there is a positive interaction between irrigation and fertilisation only if the amount of the supplied nutrient is in accordance with the need of the given plant, the scheduling is on time and if water is supplied within a range assumed to be favourable during the development of the plant. Furthermore, the productivity of the soil also affects the effect and interaction between irrigation and fertilisation.

7.1. ábra - Figure 15. The effect of irrigation on fertilisation


7. PRINCIPLES OF FERTILISATION ON IRRIGATED FIELDS

The aim of irrigation is to provide more favourable water supply for plants. Furthermore, irrigation also increases the biological activity of soils, i.e., it helps create better conditions for plants to take up available nutrients. As a result of better water supply and more intensive nutrient extraction, higher yield surplus can be achieved mainly on soils well supplied with nutrients. Higher yields withdraw significantly more nutrients from the soil which is primarily shown in the uptake a few important nutrient (nitrogen, phosphorus and potassium). On soils where irrigation farming has been performed for a longer period, the lack of other macro- and micronutrients can be observed to a larger extent.

The larger yield surplus as a result of irrigation can be expected mainly where the nutrients needed by the plants are available during plant growth. This can be reached with professional cultivation and rational fertilisation. For example, if the expected effect of irrigation is considered to be 25%, the increase of fertiliser use by a larger proportion than this could be absolutely reasonable (Figure 16).


7. PRINCIPLES OF FERTILISATION ON IRRIGATED FIELDS

7.2. ábra - Figure 16. Crop year x fertilisation x irrigation effects (Nagy, 2002)

In irrigated areas, the necessity and method of nutrient replenishment is not decided even in the case of higher nutrient withdrawal. There are different viewpoints concerning the application and proportion of organic manure and artificial fertilisers. According to certain observations, there is no significant change in the productivity and nutrient content of the soil as a result of professional irrigation and crop rotation. Certain researchers recommend mainly organic manure in the case of irrigated root crops as it increases the biological activity and the water retention ability of the soil in addition to supplying nutrients. The deep cultivation carried out on irrigated soils increases the productive layer, as well as its water storage capacity if proper quantity of farmyard manure or green manure is used.

On irrigated soils, increased amounts of trace elements have to be replenished. On soils with higher water permeability, one has to take into consideration the leaching and erosion of nutrients. In the case of surface irrigation, as a result of denitrification processes, significant nitrogen loss may occur. For this reason, it is recommended to consider these factors during the determination of the fertiliser dose which contains the amount of nitrate to be used.

Nutrient replenishment leaves a lot to be clarified in order to preserve and increase the productivity of irrigated soils. It seem probable that the majority of organic manure have to be applied mainly in irrigated areas (plots) in order to increase the organic matter replenishment, the biological activity and the physical characteristics of the soil, in addition to establishing the proper crop rotation schemes.

However, the selection of the type and quantity of fertilisers is significantly affected by soil characteristics. On meadow and kastanozem soils of good structure and nutrient supply, fertilisation for a longer period – 5-10 years – in addition to conforming to the proper crop order is more reasonable than in the case of (highly plastic or sandy) soils which are less supplied with nutrients and have weak physical characteristics. High average yields can only be provided constantly in irrigation farms if the nutrients withdrawn from the soil by the yield do not reduce the productivity of the soil. The maintenance of soil productivity can only be achieved if the nutrients available to plants are continuously provided by means of professional cultivation and fertilisation.

Irrigation does not change the fertilisation methods, which evolved in practice (basic, supplementary, row, seed-hole fertilisation, side-dressing, leaf or sprinkler fertilisation). The proper placement of fertilisers in the soil is able increase yield to a great extent and its successfulness can be further increased by irrigation, because plants mainly utilise the nutrient content of the soil layer that also contains enough accessible water. It follows partially from this and partially from the different characteristics of each fertiliser that the best solution is to plough back the whole planned amount of phosphorus and potassium fertilisers into the soil in autumn in the case of both autumn- and spring-sown crops. Irrigation provides better utilisation opportunities in the case of nitrogen fertilisers as opposed to PK fertilisers. N compounds that are easily dissolved in water and not adsorbed in the soil make it possible a differentiated use; therefore, more favourable utilisation.


8. fejezet - 8. IRRIGATION MANAGEMENT OF MAIN CROPS: POTATO1. Climate requirementsPotato prefers moderately warm, rainy and vaporous climate; therefore, regions with slightly cold temperature suit potato production the most. The limits of potato production are set by its sensitivity to temperature extremities. The foliage of potato is damaged at low temperature (-1 to -2 °C), while high temperature (26 to 28 °C) inhibits tuber development. The most suitable areas for potato production are regions, where the yearly mean temperature is between 5-10 °C and the mean temperature of the warm summer month does not exceed 21 °C.

The temperature optimum of potato photosynthesis is between 20-25 °C. However, this optimum also depends on the light intensity. In the case of higher light intensity, the optimum temperature is also higher. The efficiency of photosynthesis significantly decreases especially above 30 °C. Temperature also has a significant impact on the respiration processes of the plant: 20-25% of the produced dry matter is respiration loss in the case of 20-25 °C day and 10-12 °C night temperature. At higher temperature – which is unfavourable for potato – this value could increase dramatically. Extremely high temperatures (above 30 °C) could lead to earlier ripening of potato, especially if they are coupled with drought.

The potato’s need for climatic elements varies during the growing season. In the initial phase of development, potato is mainly sensitive to cold. In the case of cold weather, emergence is prolonged, but late spring frosts are also harmful, because the foliage might suffer frost damage, although potato regenerates rather quickly. In the middle phase of development – in the period of flowering and tuber formation – the potato is very sensitive to weather, because the most favourable weather for tuber induction is moderately warm and wet.

2. Seasonal water requirementsPotato prefers rainy and moderately warm production sites. Its water need is not too high, that of mid-ripening varieties (e.g. Desirée) is between 400-500 mm. Potato can be safely produced in regions where the amount of precipitation reaches or approaches this value. However, total water consumption is determined by many circumstances (climatic conditions, length of the growing season, soil conditions, fertilisation, irrigation scheme, etc.). It is a fact that water need is the highest during tuber formation when the optimum moisture content of the soil is 75-80% of the field capacity. The plant also utilises the moisture stock of the soil well. Despite this fact, potato should be irrigated when produced on larger areas on high quality soils.

However, it is not only the amount of precipitation that is of chief importance, but also its distribution during the growing season. Usually, the water supply of plants in the most critical periods can only be covered with irrigation. The water need of potato is not steady, the process of water consumption is mild until flowering, while it increases sharply between the beginning of flowering and the beginning of ripening. The water need slightly increases during ripening, while it levels out after ripening. In Hungary, the precipitation need during flowering and tuber induction increases in June and July. In this period, the plant demands continuous water supply, its water consumption reaches even up to 5-6 mm per day (Figure 17.).

8.1. ábra - Figure 17. Daily water use of potato during the growing season


8. IRRIGATION MANAGEMENT OF MAIN

CROPS: POTATO

(Szalóki, 1988)

3. Soil requirementsPotato can be produced on nearly any type of soil, except for high plasticity, wet and alkaline, as well as sandy soils. The most suitable soils for potato production are loose, air-permeable, slightly acidic or neutral (pH 6-7) soils with good nutrient supply.

Loose soil structure with lower plasticity is needed in order for the weakly developed root system of potato to be able to penetrate the proper depth and width in the soil. Also, these soils facilitate the undisturbed growth of the tubers. For this reason, the best quality potato is produced on sandy soils – clayey sand and sandy clay. Of sandy soils, potato can be produced in a proper quantity and quality mainly on better quality acidic sand.

On high plasticity soils, economical potato production can only be performed with irrigation and the improvement of the physical characteristics of soils, with rational cultivation and organic manure or green manure application. Potato can also be produced on acidic bog soils, but the quality of potato grown on such soils is not satisfactory; therefore, it is only used for foraging purposes. Only humus-rich sand, clayey sand and sandy clay soils are suitable for sowing potato production.

In Hungary – depending on the soil endowments, potato can be produced anywhere, but there is no region with optimal climatic conditions, as either the temperature or the precipitation supply is unfavourable. This fact is unfavourable especially in the case of producing sowing potato. The most suitable areas for potato production include Vas, Zala, Baranya, Somogy, Veszprém, Győr-Sopron-Moson, Borsod-Abaúj-Zemplén and Szabolcs-Szatmár-Bereg counties. In the other areas of the country, potato can be produced only with using the agrotechnics (mainly irrigation) most suitable for the given ecological endowments.

As a result of irrigation opportunities, the potato production areas were greatly rearranged in the past years. The sowing area of potato increased also in the counties with high plasticity soil (Szolnok, Hajdú-Bihar, etc.) where farmers used to produce only a little amount.

It is a significant obstacle to the wide extension of the irrigation of potato that there are relatively few opportunities of irrigation in the typical potato production areas where the soil is properly loose (Szabolcs-Szatmár-Bereg, Somogy county). However, this does not mean that the irrigation of potato cannot be extended significantly in these areas. It would be especially needed in sowing tuber production also because of the high yield safety of this production technological element.

4. Rooting depth and available soil waterPotato has a relatively shallow root system, 90% of the roots can be found in the top 50 cm. Potato roots grow to an effective water extraction depth of 60 cm and obtain 70% of the plants’ seasonal water from the upper 30 cm depth. Irrigation timing and amount should be based on soil moisture depletion in the top 30-45 cm for coarse textured soils and in the top 45 to 60 cm for finer textured soils (Figure 18.).



CROPS: POTATOThe shallow rooting depth is attributed to the inability of its relatively weak root system to penetrate tillage pans or other restrictive layers. Soil compaction by field vehicle traffic can greatly restrict potato root penetration. Soil water content at the time of tillage operations has a major influence on the degree of compaction resulting from field traffic. Soil compaction will reduce the ability of roots to find water in the soil. It may also influence irrigation scheduling recommendations, as assumptions of rooting depth, and hence available water, will be false.

8.2. ábra - Figure 18. Potato rooting depth(Author's note: 1” (inch) = 2.54 cm)

The irrigation amounts at each irrigation event during the growing season will vary with soil texture and growth stage (Table 10.). On most of sandy and loamy textured soils, available soil water in ranges of 45-65 and 65-85% corresponds with the field capacity levels of 70 to 80 and 80 to 90%, respectively. Please note that the available water values mentioned in Table 1are equal to 75-85 and 85-95% FC for heavy clay textured soils like clay loam, silty clay loam, silty clay or clay.

8.3. ábra - Table 10. Soil texture-based estimation of total available water and net water amounts per irrigation event during the potato growing season(Modified fromEfetha, 2011)

*available soil water, **with low (2%) organic matter, ***with high (3%) organic matter



CROPS: POTATO

5. Irrigation managementPotato irrigation scheduling for maximum profit requires that the timing and amount of water application be determined and applied to minimize soil water fluctuations throughout the growing season.

Successful irrigation management requires regular quantitative monitoring of soil water and knowledge of field crop water use, soil water holding capacity, and crop-rooting depth. Excess irrigation usually results from applying too much water at a given irrigation rather than from irrigating too frequently. This is particularly true for side-roll and hand-move sprinkler systems where soil water holding capacity and crop-rooting depth are frequently overestimated; and furrow irrigation, where application depth is difficult to control. These situations lead to plant water stress when soil water falls below acceptable limits two to three days before irrigation, and subsequent irrigation applications are in excess of soil water storage capacity. This characteristic problem can generally be attributed to inadequately designed systems, irrigation system equipment limitations, or improper irrigation management.

Determining the appropriate timing of irrigations usually involves the use of daily ET estimates based on local meteorological data to maintain a daily soil water balance throughout the irrigation season. This technique, combined with periodic quantitative measurements of soil water to adjust the computed soil water balance to actual field conditions, provides a cost effective means for determining the timing of irrigations. This approach has the added benefit of implicitly determining the irrigation application amount as well.

The basic steps involved are:

• Estimate field capacity and permanent wilting point based on the predominate soil texture in the field.

• Estimate current crop-rooting depth.

• Maintain a daily soil water balance based on published or estimated values of ET.

• Irrigate when daily soil water balance approaches 65 to 70 percent ASW, applying the net amount required to increase the soil water content to field capacity or less in the case of light, frequent irrigation.

• Periodically monitor soil water content or soil water potential and adjust the daily soil water balance to match actual field conditions.

Several methods are available to quantitatively measure soil water content. Only some are suitable for potatoes, however, because of the critical threshold level of available soil water and the limited root-zone depth. Many of the methods are labor intensive and require training, experience, and expensive equipment. This has led to the development of crop consulting firms specializing in irrigation management, which often provide crop nutrient and pest management services as well.

Tensiometers have been used to successfully monitor soil water availability in potato fields. Good contact between the soil and tensiometer tip is essential for proper operation. Tensiometers are often installed in the potato hill at two depths, such as 8 and 16 inches below soil level. Typically, the upper tensiometer is used to track soil water potential within the bulk of the root zone, while the lower one is used to determine whether soil water potential at the bottom of the root zone is increasing or decreasing over time.

A soil water release curve is needed to relate soil water potential to volumetric soil water content. The generalized soil water release curves shown in Figure 19. can be used to relate soil water potential to volumetric soil water, ASW and water deficit. These curves represent the primary soil water relationships needed for the development of an effective irrigation management program. They allow soil water content or water potential measurements to be used to calculate the net irrigation application amount needed to fill the soil water reservoir to a givenpercentage level of field capacity.

8.4. ábra - Figure 19. Generalized soil water release curves for different soil types



CROPS: POTATO

(King and Stark, 1996)

(Author's note: 1 inch = 25.4 mm and 1 foot = 30.48 cm)

The neutron probe is likely the most precise and reliable tool for soil water measurement since it determines volumetric soil water content. However, licensing, training, and associated operational costs limit their use to consulting firms and large farms.

Time domain reflectometery (TDR) offers many features that make it well suited to soil water measurement in potatoes. However, the initial equipment cost is quite high. Current research efforts to develop less expensive TDR units may make it the method of the future. Other methods are also available and may be suitable.

6. Potato growth and irrigation schedulingAll plants vary in their water requirements according to their size and growth stage as well as the length of their maturity and time of year of maximum growth. Possibly no other major crop varies in its sensitivity to water stress based on growth stage than potato. In this section, irrigation recommendations at key production periods are based on the S-shaped growth curves of roots, vines and tubers (Pavlista, 1995) (Figure 20.). Figure 20 also summarizes the relations of the production periods and the relative growth of roots, canopy and tubers to field capacity or soil moisture. The graphic model is based on determinate, mid-season varieties. Soil moisture requirements are related to different growth stages (van Loon, 1981). Quality effects of water deficit and excess during these stages are described Figure 21. (Curwen, 1994). Table 11summarizes the effects of low and high soil moisture during the potato growing season.

8.5. ábra - Figure 20. Plant growth and soil moisture model (determinate, mid-season potato variety)



CROPS: POTATO

(Pavlista, 1995)

8.6. ábra - Figure 21. Soil Moisture and Physiological Disorders in Potato

(Curwen, 1994)

In order to assure the favourable development of potato, the water content in the upper soil layer has to be kept above 62-65% of the field capacity. This way, its water need is 410-420 mm. Of this amount, the precipitation of 75% safety and the water reserves in the soil are enough to cover around 210 mm. Therefore, around 200-210 mm has to be supplemented. Of this amount, 100 mm should be provided in June and 110 mm in July.

7. Pre-planting to PlantingA pre-plant irrigation is often recommended for two reasons. First, soil moisture should be about 70-80% field capacity. This will bear-saturate the field, allowing some room for rains. This level amounts to around a quarter of the allowable deficit (AD) of the soil. Soil moisture should be acceptable to support the developing roots after planting and reach emergence. Another benefit from a “pre-irrigation” is the breaking down of clods and clumps for better planting.

8. Planting to Pre-emergence (Sprouting)The winter-spring precipitation at the time of sowing and at the initial stage of development is always enough.



CROPS: POTATOIn the case of proper soil preparation and planting, there is no need for irrigation to facilitate the emergence of potato, although it might be necessary to start irrigation with a smaller dose in the case of an extremely dry spring as drought in the spring prolongs the growing season of potato. For this reason, irrigation applied in this period results in the shortening of the growing season which is of significant importance especially in the case of the producing early potato.

Soil moisture in the top 30 cm of soil should be 65 to 80% FC. No irrigation is recommended during this production period. First, seed-pieces at a recommended size have sufficient water to support the sprout until emergence. Irrigating during this period would raise the soil moisture and lower soil aeration to a level that would support several pathogens, most notable bacterial soft rot or black leg (Erwinia carotovora), and stem and stolon canker (Rhizoctoniasolani). Excess moisture will also decrease tuber respiration, putting the seed-piece under metabolic stress. There is also good research data indicating that the soil population of Verticillium albo-atrum will increase and cause early dying at mid-season. Note, on the other hand, that a water deficit, too-dry soil, will decrease the healing of the cut surfaces of seed-pieces, inhibit root growth and increase susceptibility to soil pathogens such as Fusarium spp. and Rhizoctonia. In short, pre-plant irrigation and seed-piece water are more than sufficient to carry the sprouting tuber.

9. Emergence to Tuber Initiation (early vine growth)This is the log phase of vine growth. Roots are in the second half of their growth. During this period, the vine grows very rapidly, as much as doubling the canopy every week. With rapidly increasing foliage every week, irrigation starts low, 12-13 mm, and gradually increases every week by about 12-13 mm. At tuber initiation, about three weeks after emergence depending on variety, seed health, weather, soil, and cultural practices used, about 38 mm of irrigation is applied. A soil moisture of 70 to 80% is preferred, less than 65% FC would be considered a deficit. Water deficiency at this point would inhibit canopy and root growth, and indirectly weed control by less ground cover. An excess would retard root branching (development) by water-logging root hairs and promote nitrogen leaching. In short, with an increase in foliage and thereby transpiration, irrigation should begin and gradually increase as the canopy grows.

10. Tuber Initiation to Full BloomThe critical irrigation period is around flowering and tuber formation. The water consumption of potato could be as much as 60-80 mm if the weather is dry and warm in May which could necessitate irrigation again, as this is the period when the final number of tubers starts to form. Irrigation is the most effective in this period. There is no production site in Hungary where there is enough precipitation in this period every year. Certain model calculations also show that 1-3 occasions of irrigation would be necessary even in the Western Transdanubian region.

In determinate varieties full bloom marks the end of vine growth, while in indeterminate varieties full bloom starts a noticeable slow-down of vine growth, some branching still occurs. The first sets of tubers are being initiated and these are in a slow-growth, development stage, the lag phase of tuber growth. Irrigation becomes increasingly important and water stress becomes less tolerable. Transpiration reaches its highest rate. Optimal soil moisture is 80 to 90% FC. Water deficit would dramatically increase tuber malformations and sugar-ends. It can also weaken plants, promoting early blight. Common scab (Streptomyces scabies) attack is promoted and the longer the deficit, the greater the attack and more pronounced and enlarged the blemishes. In areas and with varieties prone to common scab, maintaining soil moisture at 90 to 95% is suggested if possible. Excessive water will increase brown center and hollow heart of larger tubers, and promote early dying of the vine. Too much loose water, swampiness, can also promote late blight, and weaken plants promoting early blight. In short, soil moisture levels must be increased and therefore irrigation is increased. Note, also that this stage of the plant often corresponds with June and July and the hottest of weather. The length of this period is also related to variety, weather and cultural practices. It may be prolonged by excessive nitrogen.

11. Full Bloom to Plant Senescence (Tuber Bulking)At this period, the canopy and roots are fully grown except for indeterminate varieties, which have considerably slowed growth. However, now, tubers are growing rapidly and are in their log phase of growth. Here, it is key to keep in mind that tubers are 76 to 82% water and this water must come from the outside, rain or irrigation. This period runs about six weeks, usually in July and August. Soil moisture should be at 80 to 90% FC. This is the period when plants have their highest demand for water and are the most sensitive to a deficit. Water deficits



CROPS: POTATOhere will reduce tuber growth but also there would be increases in tuber malformations, early dying (Verticillium and Fusarium wilts), early blight and brown spot (Alternariasolani and A. alternata), and common scab. Water excesses increases hollow heart, swollen lenticels (stomates on tuber), black leg, late blight (Phytophthorainfestans), and susceptibility to soft rot, leak (Pythium spp.) and pink rot (Phytophthoraerythroseptica). In heavy vined varieties, white mold (Sclerotinia spp.) may occur. Note that from tuber initiation through tuber bulking, evapotranspiration is very high and therefore daily water use by the plant. In short, too little water will create stress making plants susceptible to opportunistic diseases, promote common scab, and drastically reduce yields and increase culls. Excessive water will increase water rots of vines and tubers, and create conditions for late blight infestation.

12. Plant Senescence to HarvestAbundant water supply at harvest results in a prolonged growing season. If the plant population was suffering from water shortage in the first half of the growing season but there was enough water in the second half, water induces new shoots and the renewal of vegetation which is something that has to be avoided by all means. The last irrigation of potato can be finished 3-4 weeks before harvesting. This date depends on the variety, but it is usually around the middle of August. Irrigation is rarely needed before ripening. Although yield can be significantly increased with over-irrigation, but the storage of tubers could pose a problem later on. The steady (continuous) water supply of plants is of chief importance in obtaining high yields. The properly applied irrigation does not result in a prolonged growing season. In the Great Plain where the growing season of potato is shorter, even late ripening varieties can be harvested early September.

This period is characterized by dying of the vine; in the case of indeterminate, lower leaves are dying. Tuber growth slows and is in the flat stage. Tuber maturation is a common term used here as tubers settle to their maximum content of dry matter and minimum content of reducing sugars, glucose and sucrose. As the vine dies, tuber skin sets, hardens and adheres to the tuber core. Irrigation declines over this two to five week period depending on variety and climate. Soil moisture may decline to 60-65% FC. Some irrigation may benefit in wireworm and white grub control, and will avoid soil clumping making harvest easier. If the field has early blight, too much watering runs the risk of washing spores of this pathogen to the tubers. Excessive irrigation will not only stimulate tuber susceptibility to water rots, soft rot, leak and pink rot by swelling lenticels but also form an oxygen-deprived environment that promotes the pathogens the cause these rots. Water-rotted tubers can create a packaging and storage nightmare. Also too much water will increase tuber susceptibility to shatter bruise due to raised tuber water content. The reverse, too little soil moisture, can increase internal black spot bruising (IBS) as well as delaying skin set. Skin russeting of russet varieties is decreased.

8.1. táblázat - Table11. Water Deficit/Excess Effects during the Potato Growing Season (Curwen, 1994)

Production Period & Plant Growth Phases

Preferred Soil Moisture Moisture Deficit Effects Moisture Excess

Pre-Plant Preparation 70-80% FC soil clumping

poor root growth

muddy soil and

delayed planting

Pre-Emergence

Root = lag-log phase

Canopy = lag phase

65-80% FC poor seed healing

poor sprouting

poor root growth

susceptible to rot

poor seed health

poor sprouting

poor root branching

high soil pathogens

Pre-Tuber Initiation

Root = log phase

Canopy = log phase

70-80% FC poor root growth

poor canopy growth

late tuberization

poor root branching

stolon/stem canker

blackleg on stolon



CROPS: POTATO

Tuber Initiation

Root = flat phase

Canopy = log phase

Flower = blooming

Tuber = lag phase

80-90% FC leaf aging and wilt

early blight

common scab

late tuberization

tuber mis-shaping

tuber sugar-ends

leaf aging

hollow heart

blackleg

early blight

early dying

late blight danger

Tuber Bulking

Canopy = flat phase

Tuber = log phase

80-90% FC leaf aging and wilt

wilt diseases

early dying

early blight

brown spot

common scab

poor tuber growth

tuber mis-shaping

leaching N

swollen lenticels

hollow heart

blackleg

late blight

soft rots (field)

white mold

Plant Senescence

Canopy = dying

Tuber = maturing

60-70% FC poor tuber maturity

late skin set

high skin peeling

poor skin russeting

high bruising (IBS)

soft rots (storage)

tuber early blight

high shatter bruise

stolon and stem cankers = Rhizoctoniasolani; blackleg = Erwinia carotovora; early blight = Alternariasolani; common scab = Streptomyces scabies; early dying = complex, primarily Verticillium dahliae; late blight = Phytophthorainfestans; wilt diseases = includes Fusarium, rhizoctonia, and Verticillium wilts; brown spot = Alternariaalternata; soft rots = include Erwiniacarotovora (bacterial soft rot),phytophthoraerythroseptica (pink rot), and Pythium spp. (leak); white mold = Sclerotiniasclerotiorum

13. Management under limited water supplyMany research studies have focused on investigating the effects of water stress timing on tuber yield and quality. When water resources are limited, the best practice is to schedule irrigations to cover the period from tuber initiation through mid-bulking, and select cultivars that use less water and/or are less sensitive to water stress.

Results from a few studies have indicated that water stress can best be tolerated during the early vegetative growth and late tuber bulking. Actual water stress effects on yield and quality depend on ET rate, soil water holding capacity, irrigation frequency, crop growth stage, and cultivar.

14. Recommended irrigation methodsPotatoes can be grown with all types of irrigation, however, some are better suited than others for consistently obtaining high quality tubers. The water sensitive nature of potatoes, combined with its shallow root zone, favors irrigation systems that are capable of light, frequent, and uniform water applications. Using these criteria



CROPS: POTATOas a basis for ranking the suitability of common irrigation methods, the order of preference from highest to lowest would be: drip, solid-set (portable), linear-move, center-pivot, side-roll, hand-move, and furrow. In practice, economics are the overriding factor in irrigation system selection. Compatibility with soil type, crop rotation, and cultural practices are also important considerations. Buried drip is expensive, incompatible with conventional potato production practices, and is not suitable for establishing stands of some crops commonly grown in rotation with potatoes, especially in coarse-textured soils. Solid-set portable is expensive, as is linear-move. Center-pivots are highly susceptible to excessive runoff under the outer towers unless conservation tillage practices, such as basin or reservoir tillage, are utilized. Side-roll and hand-move sprinkler systems are prone to wind skips under the windy conditions. Furrow irrigation is susceptible to poor water application uniformity, excessive deep percolation, and leaching. Sprinkler irrigation is the most common method used for potatoes, with center-pivot, side-roll, and hand-move being widely used(Figure 21.).

Under Hungarian conditions, sprinkler and drip irrigation can be recommended in potato production. Usually, only sprinkler irrigation can be used on sandy soils.Today, sprinkler irrigation is becoming increasingly widespread. Advantages of this method:

• potato responds to multiple occasions of applying smaller irrigation water doses the best,

• more balanced water distribution, the amount of water can be well regulated,

• it deteriorates the soil structure less and the moisture condition of the soil can be maintained at the desired level,

• helps applying nutrients,

• it can also be used on uneven soil surfaces.

The sprinkler and micro-irrigation proved to be great in irrigating early forced potato. The sprinkler heads dose the irrigation water evenly and at low intensity. The system is environmental friendly and it reduces the water and nutrient use. Furthermore, it can provide a favourable microclimate in the case of dry and warm climate. The low intensity greatly reduces soil compaction in the root zone, thereby contributing to the maintenance of the optimal soil structure.

Drip irrigation is also used currently. This irrigation method is especially economical and it greatly reduces the water use per area unit. Furthermore, drip irrigation does not deteriorate the soil structure and there is no loss from evaporation. It is a further advantage of this method that the relative humidity of the air increases above the irrigated area for only a short period; therefore, it does not contribute to developing potato blight (Phytophthorainfestans). If this irrigation type is used, potato should be produced in a twin row way.

8.7. ábra - Figure 21. Criteria for ranking the suitability of irrigation methods in potato production

(Source: own editing on the basis of King and Stark, 1996)



CROPS: POTATO

15. Irrigation of early forced potatoThe production and irrigation of the early forced potato is similar to conventional potato production in its principles. After the planting around 10th to 20th March, 4-5 occasions of irrigation (15 mm) are needed in April and May. The last irrigation can be finished only 10-14 days before harvest.

16. The connection of irrigation with other production technological factorsDuring the irrigation of potato, one has to take into consideration the furrowed character of production. Practically no surface and furrowed irrigation takes place, because the high plasticity soils in the Great Plain are not potato production areas. In the case of sprinkler irrigation, the movement of irrigation machinery has to be assured in the potato rows, bearing in mind the typical needs of each machine type. Furthermore, it can also be established that the planting density of potato is usually 15-20% higher in the case of irrigation.

If irrigation is applied, nutrients are partially leached from the soil and they are taken up by the root of the plant more actively; therefore, more fertiliser should be applied. Irrigation improves the efficiency of fertilisation and the common use of higher fertiliser doses and irrigation exceeds the impact that could be reached separately.

17. The effect of irrigation on yield and the quality of potatoPotato calls for steady water supply; therefore, drought or too much precipitation (or over-irrigation), as well as the alternation of dry and wet periods have an adverse impact on both yield quantity and quality. The various tuber disorders (external and internal quality problems) which reduce the marketability of the potato are in connection with either water shortage, water abundance or the fluctuating soil moisture content. This correlation is not always obvious and totally clarified. These quality problems are caused by the level of the plant’s supply with water in addition to several other factors (e.g. temperature, nutrient supply).

Irrigation greatly increases potato yield. This increase is 30-50% in most years at the large scale. However, it has to be noted that these numbers are usually the results of irrigation that was applied at an improper technical and agronomical level. Experiments show that 50% yield increase on sandy soils, 60% on clay soils and 90% on meadow alluvial soils are realistic objectives if irrigation is applied.

The yield increase is mainly the result of the increase of the average tuber weight. As a result of irrigation, the number of tiny tubers increases. While the proportion of tiny tubers could be up to even 40-50% of the total yield under non-irrigated circumstances especially in dry crop years, this value is less than 25% in an irrigated population with proper water supply, although it might decrease below 10% in the case of certain varieties. Furthermore, the tuber infection caused by Streptomyces scabies can also be prevented with constant water supply in accordance with the plant need.

In crop years when the yield is very low without irrigation due to drought and irrigation could result in rather high yields, the starch content of tubers in the irrigated population is lower than that of the non-irrigated population. However, if there is no great drought in the second half of the growing season after tuber induction, there is no difference between the starch content of the irrigated and the non-irrigated potato yield. In the case of improper irrigation, not only the starch content of potato might decrease, but even the distribution of starch could be uneven in the tuber tissues.

The following quality problems mainly develop due to inequalities in water shortage:

Development of scabby patches. The scabby patches on the tuber surface are caused by Streptomices spp. The most efficient protection is the production of resistant varieties and the irrigation launched at the time of tuber induction.

Secondary growth and glassiness. The sudden growth of the volume of the internal tuber tissue as a result of water abundance after the end of water shortage leads to tuber cracking. The development of such deep cracks is increased by nitrogen over-fertilisation, too.



CROPS: POTATOBrown centre and hollow heart of tubers. In the too wet soil, white spots can be seen on the peel of the tuber, which are enlarged lenticels. These swollen and expanded lenticels do not cause any problem on their own, but they could lead to fungal and bacterial infections (Erwinia, Ralstonia, Phytophtora), setting off rotting processes in the field and the warehouse.

All three discussed physiological diseases (disorders) which cause severe damage could be prevented if one avoids the development of overly wet conditions (over-irrigation) and loose soil structure is established with proper cultivation, farmyard and green manure application and mineral fertilisation (chalk, dolomite) on acidic soils.

18. SummaryPotatoes are more sensitive to water stress than most other crops, have relatively shallow root systems, and are commonly grown on coarse-textured soils. The primary goal of potato irrigation management is to minimize soil water fluctuations and maintain available soil water within the optimum range of 65-85%. Irrigation systems best suited to this task are those that are capable of light, uniform, and frequent water application. An effective irrigation management program must include regular quantitative monitoring of soil water availability, and scheduling irrigations according to crop water use, soil water holding capacity and crop-rooting depth.

Using optimal irrigation strategies with potato can mean a healthy crop with high marketable yield potential. In addition to ensuring that the potato crop is well-fertilized and well-protected from pests, growers are encouraged to properly manage irrigation by regularly monitoring soil water to ensure that the availability of water does not become a limiting factor in producing a high-yielding potato crop.


9. fejezet - 9. IRRIGATION MANAGEMENT OF MAIN CROPS: SUGARBEET1. Climate requirementsSugarbeet needs long day illumination. In shiny weather, sugarbeet produces root with higher sugar content if its leaves are not damaged by diseases and it does not suffer from water shortage in the growing season. Around 15 hour illumination per day is needed for optimal photosynthesis. During the growing season (170-200 days), sugarbeet needs a heat sum of 2400-2600 °C. The heat needs changes in the different phases of crop growth. Germination starts at 4-5 °C and reaches an agronomically favourable pace at 6-8 °C. There is a close positive correlation between temperature and germination. At 4-6 °C, 15-20 days are needed for the emergence of sugarbeet, while even 4-5 days are enough at 15 °C. Under the Hungarian circumstances, sowing should be started close to the first value, because soil warms up quickly and the drying out of soil might inhibit germination and emergence later.

After emergence, the quick spring warm-up is favourable for crop development. From emergence to foliation (early June), sugarbeet needs 12-18 °C. Cooling down in April always causes damage to the crop population because development stops and crops weaken which could contribute to Pythium de Barianum infection and the perishing of stems. Sugarbeet develops well in the summer months at 19-22 °C. The great heat causes the withering and drying of leaves. By the end of the growing season (in September), the moderately warm days and cold nights help the incorporation of sugar. Under such circumstances, the intensity of respiration is lower due to the cooling down at night, but the photosynthesis does not stop; therefore, the root grows and the dynamics of sugar incorporation is also favourable. Warm days and nights in September inhibit the increase of the sugar content due the rather intensive respiration at night.

2. Seasonal water requirementsThe water need of sugarbeet during the growing season is 550-600 mm. The peak period of water need is July-August, the mean daily water need is 5-6 mm. During intensive transpiration, plants evaporate up to even 6-7 mm per day. During these two months, sugarbeet takes up half its total water need (Figure 22). For this reason, there can not be such a year (even with abundant precipitation) when there is no need for the irrigation of sugarbeet with smaller or larger water doses.

9.1. ábra - Figure 22. Daily water use of sugarbeet during the growing season



CROPS: SUGARBEET

Water need gradually decreases in September and October. However, this decrease has a different rate than in the case of plants, which are getting closer to the end of the generative phase, e.g. maize. For this reason, sugarbeet is able to take up considerable amounts of water even in September and October, if the weather is rainy. However, its water utilisation is not efficient, since the foliage and the root mass increase, while the sugar content decreases.

Due to the large water need of sugarbeet, the driest regions of Hungary are not suitable for its production. In areas with 550-600 mm or more precipitation per year, production is safer and has better results. The inconstant summer precipitation, which is rather typical of the Great Plain, is not favourable for sugarbeet production. If the precipitation following a dry period is repeated several time, the plant is induced to develop newer leaves, which results in reduced sugar production.

Sugarbeet is a deeply rooted plant and its water suction capacity is also good; therefore, it is able to use a significant amount (200-300 mm) of the moisture stored in soils with proper water management. It follows from this that sugarbeet is not a good previous crop for most plants, as it dries out the soil deeply.

The static water need of sugarbeet is 60-65 which shows that its need concerning the air supply of the root zone is at least as high as in the case of water supply.

3. Soil requirementsSugarbeet is one of the most sensitive plants to soil characteristics. Sugarbeet cannot be produced in the case of weak soil characteristics and on soils with unfavourable water management, but on soils with deep fertile layer, enough humus content, crumbed structure, good water and nutrient management. Soils weakly supplied with chalk, acidic, too wet, cold, high plasticity soils, soils with shallow fertile layer and loose soils are not recommended to be used for sugarbeet production. However, chernozem, meadow chernozem, chernozem meadow, alluvial chernozem and brown forest soils are ideal for sugarbeet production. The good culture condition of the soil is also an important factor. Sugarbeetcannot be sown on unkempt soil which is prone to weed infestation and contains chemical residues. During the selection of the area, one has to pay attention to choose a sugarbeet field that is not far from the road, the takeover or storage location, because that will increase costs and make harvesting and transport more difficult.

4. Rooting characteristics and available soil waterThe sugarbeet plant has an extensive tap root that can penetrate up to 180 cm into the soil if it is not limited by soil compaction or lack of water. A layer of dry soil will act just like a severely compacted zone of soil and limit root development. As sugarbeet roots penetrate deeper into the soil, the plant uses more energy to transpire. This is why normal irrigation management calls for depleting only the top 90 cm of the soil profile before irrigating.



CROPS: SUGARBEETPlants remove water from the easiest location in the soil profile first. This means water near the surface is used first and water stored deeper in the soil profile is used second. This process continues throughout the soil profile until water in the first foot is well below the 50 percent depletion level. Even though water can be taken from deeper in the soil profile, limiting the water management soil profile to 90 cm avoids excess water stress and provides some reserve when irrigation is delayed (Figure 23). Just as water stress early in the season can limit root development, irrigation that replenishes only the upper layer of soil discourages root development at the deeper depths of the soil profile. Poor irrigation practices or soil compaction will change where the sugarbeet root system develops and where water is obtained. Irrigation management should strive to replace water in the active root zone throughout the entire growing season.

9.2. ábra - Figure 23. Percent water extraction of sugarbeet in the top 120 cm of a soil profile having adequate water available (Yonts and Palm, 2008)

(Author's note: 1 ft (foot) = 30.48 cm)

In many locations, it is suggested that room be left in the soil profile tostore potential rainfall. However, in the growing sites of the Great Hungarian Plain, rainfall probabilityis low enough during the bulk of the growing season that this practice is notalways suggested. According to different soil textural classes, in most cases there is storage availablefor 11 to 28 mm of water. Early or late in the growing season, this practicemay provide a means to reduce irrigation.

In connection with this method, the average available soil water (ASW) of the sugarbeet root zone should be maintained between 65 and 85 percent during the active growth period for optimum results. In practice, ASW in the monitored soil profile will fluctuate above and below this range for short periods of time immediately before and after irrigation (Table 12.).

The high sensitivity of the beet root to airless conditions calls for the reduction of the irrigation water dose. Therefore, the quantity of water applied in one turn cannot exceed 20-30 mm. However, due to the small irrigation water dose, shorter irrigation turns and the increased number of irrigation are needed. As a matter of course, the traditional two or three occasions of irrigation cannot be provided in this case. The water amount needed by sugarbeet during its growing season can be covered with five-six occasions.



CROPS: SUGARBEETSugarbeet irrigation cannot be performed on the basis of only an irrigation norm or some other prescription. Irrigation doses need to be determined independently in each production area each year. The aim is to provide moisture that continuously keeps the soil damp. On meadow and meadow chernozem soils, doses higher than 20-25 mm should not be applied in one turn on sugarbeet fields, while this value is 20-30 mm on chernozem and alluvial soils. Even the irrigation of such amounts is only profitable if it is evenly distributed. The water norm of the first and last irrigation should not exceed 15-20 mm.

9.3. ábra - Table 12. Soil texture-based estimation of total available water and net water amounts per irrigation event during the sugarbeet growing season (Source: own calculation based on data of Yonts and Palm, 2008)

*available soil water, **with low (2%) organic matter, ***with high (3%) organic matter, ****2 irrigations per application will normally be required

5. Irrigation managementSugarbeet has high water need and it utilises irrigation water efficiently. In order to exploit the favourable biological characteristics, one has to focus on the following aspects in irrigated sugarbeet production:

• Soil moisture levels should be maintained above 65% available moisture,

• Sugarbeets develop in an active root zone of 100 cm with 70% of the water drawn from the top 60 cm of this root zone,

• Irrigation has to be applied on the basis of the dynamic water need of sugarbeet,

• In order to cover the water need, it is important to know the available moisture content stored in the significant (150-200 cm) layer of the soil in addition to the precipitation data,

• Sugarbeets are most sensitive to moisture shortages and salinity in the early growth stages (germination and seedling),

• The optimum root development has to be facilitated: if the weather provides abundant or proper soil moisture, one should not start sugarbeet irrigation too early, so that plants can develop strong and hardened roots in order to be able to utilise irrigation water more successfully later on,

• If the spring is dry, artificial water replenishment has to be started early, otherwise it is not possible to prevent the irregular development of sugarbeet,

• A dark green color of the beet leaves is an obvious sign of stress. At his point, irrigation should begin immediately.



CROPS: SUGARBEET• In the first half of the development of sugarbeet, special attention must be paid to determining the single

irrigation dose in a moderate way,

• One has to take into consideration the fact that sugarbeet is very sensitive to the lack of air of the root zone in addition to its large water need which increases the risk of various root diseases especially at young age,

• The irrigation water has to be applied steadily in the sugarbeet field,

• Under-irrigating will cause stress and reduce yield, while over-irrigating near harvest reduces sugar content,

• In irrigated fields, one has to pay utmost attention to forming balanced crop populations (80-90,000 plants per hectare),

• One should avoid irrigation after mid-August, as it results in protracting the date of technical ripening which usually results in the reduction of the sugar content of the sugarbeet as a consequence of irrigation,

• Sugarbeet should not be irrigated three weeks before harvesting.

6. Early season water managementCovering the water need calls for different irrigation scheme in each crop year. However, some general principles should be taken as a basis.

The impact of irrigation greatly depends on the proper choice of the first and last irrigation date in a growing season. In the case of average weather, on soils with good water management, the winter-spring precipitation is enough not only to provide steady emergence but also to facilitate the strong initial development of sugarbeet. The first irrigation should not be performed too early, except if the spring is extremely dry. If the lower layer of the soil is wet, sugarbeet penetrates deeper layers with its taproot in order to access water. Early irrigation provides the plant with water in the upper layer of the soil but makes it compacted and airless (Figure 24.); therefore, it does not make it necessary to develop deeper root and it even inhibits its growth. For this reason, early irrigation inhibits the development of the gradually thinning, regular root body that is typical of sugarbeet. However, there are years when the spring is dry and the winds dry out the shallow soil layer in the phenophase of sowing and emergence. In cases like this, small dose or repeated irrigation can provide steady emergence. This is an important factor, since the perfect plant population is a prerequirement of root yield that has good quality and quantity parameters.

There are pros and cons to irrigating sugarbeet for germination and emergence. The additional amount of labor and energy required is the primary reason given for not irrigating after planting; however, with irrigation, plant stand and vigor can be improved during this critical growth period. The lack of soil water during germination will often result in less than adequate plant population and seedlings vulnerable to disease.

If sugarbeet seed is being planted into dry soil with no chance of germination, serious consideration should be given to applying a pre-plant irrigation to fill the top 30 cm of the soil profile. The advantages of pre-plant irrigation are:

• available water below the seed,

• better depth control while planting,

• placing seed in moist soil,

• no immediate post-plant irrigation required, which leaves soil particles intact to reduce potential wind erosion, and

• soil temperature can return to a normal state before planting.

By filling the top foot of soil, adequate water is available for the seed to germinate and emerge without applying excess water after planting and creating a potential crusting problem (Figure 25.).

InFigure 24, sprinkler irrigation is applied after planting. If a light irrigation of 12 mm or less is used, only a small portion of the soil profile will be filled and evaporation quickly drys the soil surface. Evaporation occurs to a deeper depth compared to the pre-plant sprinkler irrigation example (Figure 25.) because there is not



CROPS: SUGARBEETadequate soil water below the seed. The only option we have once germination has begun is to continue light irrigation applications to try and avoid excessive water stress. With each added irrigation, the soil surface becomes consolidated, making emergence more difficult and increasing the potential for soil erosion due to wind.

9.4. ábra - Figure 24. Water movement in the 30 cm soil profile: sprinkler irrigation is applied after planting(Yonts and Palm, 2008)

In Figure 25, we have the same spring conditions, only this timesprinkler irrigation is applied before planting to partially refill a portion of the soil profile. When the seeds are planted, the soil profile has not been filled to field capacity, but adequate water has still been made available below the seed. Upward movement of water occurs to meet soil evaporation losses. Applying a light irrigation now will refill the entire soil profile that surrounds the germinating seed. In this scenario, applying some of the water before planting avoids repeated irrigations after planting. Reducing sprinkler irrigations after planting allows the surface soil structure to be maintained while making soil water available for germination.

Before adopting irrigation for germination and emergence as an every year practice, ask this question: “Have I done what is necessary to conserve precipitation that fell during the fall, winter and spring?” At a given location, the decision to irrigate or not to irrigate should be based on the amount of water in the soil at planting.

An example of one method to conserve soil water would be to create a firmbed in the fall before spring planting. The seed bed is firm yet several freezethaw cycles will have created a mellow seed bed at seeding depth. Soil water is below the seed and irrigation will be needed only if drying conditions exist. Compare this system to multiple tillage operations in the spring where much of the soil water that did accumulate over the fall and winter is lost to evaporation due to repeated cultivations of the soil.

9.5. ábra - Figure 25. Water movement in the 30 cm soil profile: pre-plant sprinkler irrigation (Yonts and Palm, 2008)



CROPS: SUGARBEET

7. Mid-season water managementIt is also important not to be late with irrigation, because if one sets off the irrigation equipment only when the sugarbeet population is suffering from water shortage, irrigation will not have any yield increasing effect. In years with average water supply, the water need of sugarbeet can be covered if the first irrigation is performed mid to late June. The transpiration of the plant population is more moderate until this date, while soil moisture is usually still available as a result of winter-spring precipitation.

July-August (and, to a certain extent, even early September) is the main water consumption period of sugarbeet. In this period, one has to take care of keeping the upper 30-40 mm soil layer dampcontinuously. This can be reached by repeated irrigation, depending on the summer precipitation in the given year. One should perform irrigation at a frequency that never actually makes up the water shortage, but it rather prevents water shortage from happening.

8. Late season water managementAlso, special attention must be paid to properly selecting the date of the last irrigation as irrigation inducessugarbeet to develop leaves constantly, while delaying the incorporation of sugar into the root. Leaf development can be considered a productive process as long as there is enough sunshine (usually mid-August in Hungary). However, it is an unproductive process if there is not enough sunshine, because the previously produced useful substance, which is usually stored in the root will be withdrawn. For this reason, one has to conform to the rule that the last irrigation of sugarbeet should take place mid-August. The soil profile filled up with the last irrigation stores enough moisture until the harvesting of sugarbeet. In the case of extremely dry and warm autumn weather, it is also possible to irrigate later, but it should be finished three weeks before starting to harvest.

The delayed last irrigation could lead to a decline in quality. In the case of a dry autumn, sugarbeet can be “fattened” with irrigation that is stopped relatively soon. In this case, sugarbeet regains its activity as a result of irrigation. The weight of sugarbeet harvested at this point is higher, but its quality is weaker, due to the extractable sugar content.

9. Sprinkler Irrigation Water ManagementSugarbeet needs steady irrigation at all times; therefore, only the irrigation equipment that are technically capable of applying irrigation water steadily can be used for this purpose. For this reason, mainly linear and center pivot sprinkler irrigation systems can be used.

Sprinkler irrigation is often viewed as a superior irrigation method. Unless managed correctly, all that it may save is labor without giving any advantages to better water application and yield. The mistake often made with center pivot irrigation is not knowing the amount of water being applied and relating that value back to what is known about the evapotranspiration rate.



CROPS: SUGARBEETAnother aspect to consider with sprinkler irrigation is placement of sprinkler or spray devices. The industry has gone through major changes and has seen sprinkler devices placed on drops below the sprinkler pipeline and near the crop canopy in an effort to reduce water loss. It recently found that losses, due to evaporation and drift from sprinkler systems,are much smaller than was first estimated. Changing from impact sprinklers to sprinkler devices on drops results in water savings of 3-5 percent. If the entire canopy is wetted during irrigation, height of the sprinkler devices above the canopy will not be critical in further reducing water loss. In other words, closer is not necessarily better.

Figures 26-28 show how sprinkler device and placement can impact irrigation runoff. The dashed line in each figure shows the water application rate for that particular sprinkler device. The solid line is the infiltration rate curve for a silt loam soil. When the application rate exceeds the intake rate of the soil, water appears on the soil surface. If this application rate continues, runoff will occur.

9.6. ábra - Figure 26. Effect of Sprinkler Device Placement on Water Application (location above ground: 1.8 m, 12 m wetted diameter and application time: 22 minutes)

(Yonts and Palm, 2008)

(Author's note: 1 in (inch) = 25.4 mm)




CROPS: SUGARBEET






InFigure 26, the sprinkler device is designed properly for the soil by using a sprinkler device that gives a 12 m diameter of throw. In Figure 27a spray device is selected which gives a 6 m diameter of throw. As can be seen, the shaded area in the figure shows the amount of water being applied that has the potential to runoff. Finally, inFigure 28, the spray device is lowered from a 1.8 m height to a 0.9 m height. This further reduced the diameter of throw and increased the potential for runoff. If runoff is observed from a sprinkler system, carefully consider the location of the sprinkler devices and the type of device being used.



CROPS: SUGARBEET

10. Water management impact on diseaseSeedling diseases in sugarbeet are encouraged by wet soil conditions during emergence and early plant growth. Water application is often necessary to establish a stand of sugarbeet; however, to avoid potential disease problems, irrigate before or soon after planting with adequate water to meet plant requirements for the first three weeks after emergence. Frequent, light applications of water, specifically with a center pivot, for germination and emergence provide ideal conditions for the development of damping off and root rot disease.

Cercospora leaf spot can be indirectly affected by irrigation. For Cercospora leaf spot, the irrigation itself does not determine whether the disease will develop; however, if a spray program is started to control the spread of Cercospora, sprinkler operators should pay particular attention to the timing of fungicide applications. There is some evidence that the water applied to the leaves can wash some of the chemical control off and reduce effectiveness. Consider timing irrigations to complement the control program. Irrigate as much as possible before fungicide application, then allow several days without applying water. This is especially important if conditions are right for Cercospora leaf spot development.

Powdery mildew, like Cercospora, does not develop as a direct result of irrigation; however, sprinkler irrigation can wet leaves and wash organisms from the leaves. This may hinder, but not stop, the spread of the disease. To control powdery mildew, fungicide is applied to the leaves. Allow adequate time for the fungicide to dry on the leaves before irrigation. Once dry, the material should remain on the leaves even after irrigation. Since powdery mildew thrives in warm dry conditions, lighter more frequent sprinkler irrigations may contribute to lessening disease spread due to moist leaf conditions.

The varieties produced as a result of modern breeding have high yield capacity. However, increased attention must be paid to their resistance to Cercospora beticola. This is a general need, but it is especially important in irrigated areas, due to their more vaporous microclimate. Today, most varieties have the necessary extent of resistance.

Rhizomania is present on all Hungarian fields to a smaller or greater extent. The fungus spreading the virus (Polimyxabetae) profilerates more in wet soil; therefore, the danger of infection also increases. For this reason, one must conform to the requirement that only rhizomania resistant varieties can be grown under irrigated circumstances.

11. Special requirements of irrigationDue to the one-sided soil use, the wrong choice of cultivation tools, the high number of operations and the compaction of machines, the physical condition of soils gradually deteriorated during the past decades. Our soils became compacted and their proneness to compaction increased. This condition could become especially dangerous under irrigated circumstances; therefore, performing deep or deepening loosening is an obligatory task on fields designated for irrigation.

One has to exploit also the soil condition improvement impact of organic manure application. Organic manure has to be applied during the growth of the previous crop; therefore, the expected impact can be obtained without having to face increased risk of weed infestation.

In addition to extracting nutrients, lime fertilisation also improves the maintenance of the structuredness of soils. Sugarbeet is commonly known as a plant that needs Ca; therefore, 3-5 tons per hectare sugar works caustic sludge has to be applied on sugarbeet production sites mainly under irrigated circumstances.

12. SummaryUnderstanding of water requirements and proper irrigation techniques in sugarbeet is important for optimum sugar production, since total sugar yield is related to root production and maximum root production is related to limiting plant stress.

The goals of water management should be:

• To maintain otimum soil water conditions thorough the growing season

• To promote a good rooting system



CROPS: SUGARBEET• To reduce soil and water degradation (erosion, soil compaction, leaching of fertilisers and chemicals)


10. fejezet - 10. IRRIGATION MANAGEMENT OF MAIN CROPS: ALFALFA1. Climate requirementsAlfalfa is a rather plastic crop in terms of climate need. Its water resistance is especially important in addition to its drought sensitivity. However, its winter resistance is not only the characteristic of different ecotypes, but it can also be affected by the used agrotechnical solutions. As a matter of course, this drought resistance has to be evaluated in terms of different types, which were developed under given ecological circumstances. Drought resistance primarily means that alfalfa does not perish in the majority of soils in spite of the great drought, but they still vegetate and their dry matter production is reduced to the minimum. Alfalfa is able to grow deep roots and take up more water in soils with deep fertile layer, while its rooting ability is lower in soils with shallow fertile layer and the capability of the plant to cover its water need is also lower. Therefore, alfalfa might perish in patches when there is a dryer crop year. The water need and even the transpiration coefficient of plants belonging to the Fabaceae family is twice or three times as much as that of cereals. The contradictions within the family are resolved by the rooting depth of the species and the suction pressure of the root (pea, alfalfa). It seems controversial that alfalfa eventually belongs to the high water need plants of field crops.

Alfalfa has different water need from growth to growth. The lower water need of the first growth can be explained by the lower spring air temperature and the lower potential evaporation. The reason why the 4th and 5th growth usually requires less water is that their yields are also lower.

The transpiration coefficient of alfalfa is between 600-700. Its water utilisation efficiency is poor which stems not only in this physiological characteristic, but also the repeated sprouting after multiple reapings. The static water need of alfalfa is between 70-75%. Alfalfa cannot tolerate airless soil conditions. Under such circumstances, the thinning of the population speeds up. Airless soil conditions also inhibit the rhizobial activity.

2. Water use characteristicsBecause it has a longer growing season, alfalfa can use more water annually than other crops.Alfalfa varieties grown in Hungary will use approximately 800 to 850 mm of water in an average growing season.Irrigation management must consider characteristics such as water requirements (including seasonal, total and daily water use), root system development, and critical stages of growth as well as soil characteristics, the irrigation system, and the available water supply.

A water-use pattern for alfalfa is shown inFigure 29. This pattern shows typical daily crop evapotranspiration(ET) throughout the growing season. The amount of water used by alfalfa varies from season toseason and location to location, but will follow this samegeneral pattern. The primary climatic factors affecting themagnitude of water use are air temperature (greater withhigher temperatures and less with cooler temperatures), solarradiation and wind speed. Availability of soil water also willdirectly affect crop water use.

10.1. ábra - Figure 29. Seasonal water-use pattern of alfalfa



CROPS: ALFALFA

(Alam and Rogers, 2009)

(Author’s note: to convert inches to mm, multiply x 25.4)

Alfalfa does not have a stage of growth that is extremely critical or less sensitive to water stress. If water is not available, the plant will slow or stop growing and go dormant. When water becomes available, growth will resume. However, lack of moisture will reduce crop ET and yield. Drought-stressed alfalfa matures earlier, thus forage quality will peak earlier and degrade more rapidly than under normal conditions.

Alfalfa begins using water when plant growth starts inthe spring. Growth typically beginsin early to mid-April. Initial crop water use is small becausegrowth is slow and temperatures are cool. As temperatures riseand the rate of growth increases, daily water use increases.The water use rate rises sharply and reaches a peak at canopyclosure near the pre-bud stage at 25-30 cm in height.

The peak daily water use of alfalfa normally will range from 7.6 to 8.9 mm per day in July and August, but may be as high as 12 mm during hot, windy, and dry days. Peak rates of 12-13 mm per day are not uncommon, but they seldom last more than a day or two.

Water use may drop slightly as harvest approaches, butit drops sharply when alfalfa is cut because transpiration isminimal when most of the leaf area has been removed. Afterharvest, alfalfa re-growth begins and the water use cyclebegins again. This cycle is repeated for each cutting (i.e.,every 30 to 40 days).

3. Soil requirementsThe lack of alfalfa’s sensitivity to climatic factors does not refer to soil need at all. It is the uniform opinion of every researcher and specialist that alfalfa is sensitive to both the physical and chemical characteristics of the soil and the subsoil. Under Hungarian circumstances, sativa species can mainly be produced on good structure kastanozem soils with deep fertile layer, since alfalfa has a pole root which penetrates deep. The prerequirement of successful alfalfa production is that there should be no closing layer in the subsoil, so that the alfalfa roots can penetrate as deep as possible. It is very important that the groundwater level of the area should not be high and there should be no stagnant water. Also, there should not be any extreme fluctuation in the groundwater level.

Higher chalk content is the general need of alfalfa (both Medicago sativa and M. varia). The chalk need of alfalfa is significantly higher than that of pea. The most favourable soils for alfalfa production are those between 6.2-7.8 pH. Alfalfa is especially sensitive to the chalk content of the subsoil. The minimum required chalk content of alfalfa production is 0.02-0.03%.

4. Rooting characteristicsThe active roots of the alfalfa plant can penetrate 250 to 350 cm in deep, well-drained soils. However, alfalfa will obtain 75 to 90 percent of its moisture from the upper 100 cm of soil. Water in the lower portion of the root



CROPS: ALFALFAzone is especially important if the crop’s water demand cannot be totally supplied by the irrigation system during peak water use periods.

During the growing season, irrigation normally will not supply water any deeper than 100 cm in the soil profile. Irrigation and precipitation in the fall or early spring can supply water to the deeper portions of the soil profile for use during the growing season. A clay pan or other restrictive soil layers can limit the effective root zone depth. Shallow root zones require smaller and more frequent irrigations.

When irrigating alfalfa, only the top 75 to 100 cm of the root zone should be considered as the managed root zone in an irrigation scheduling analysis. Water is used below this depth, but the managed root zone contains more than a majority of the plant’s roots, and approximately 80 percent of the water originates from this area (Figure 30.).

10.2. ábra - Figure 30. Alfalfa managed root zone for irrigation

(Source: http://weru.ksu.edu)

Research shows that if water is readily available to at least half of the roots, alfalfa plants experience little or no stress. Consequently, if water is available in the managed root zone, little water is used from the lower depths.

5. Special Alfalfa Irrigation CharacteristicsA number of important factors cause alfalfa irrigation to differ from other crops. These factors include:

• Alfalfa is a perennial crop with a potential deep-root system that can use moisture deep within the soil profile,

• Alfalfa is considered drought tolerant because it is able to use up to 70 percent of available soil water without undue stress or production loss. If the crop becomes stressed beyond this limit, plant growth stops until more soil water is available,

• Alfalfa can be considered as a crop choice for irrigators with limited water supplies because, water stress during one production cycle may cause loss of yield for that cycle but the crop can survive a dry period and recover during the next cutting for a good harvest if the water stress is removed,

• Multiple harvests prevent irrigation for about 7 to 10 days per growth cycle,



CROPS: ALFALFA• Frequent heavy equipment traffic across an alfalfa field causes soil compaction and often forms a crust on the

soil surface. This crust could result in reduced soil water infiltration rates as stands age,

• Over-irrigation can quickly injure alfalfa plants and encourage weed invasion, especially right after harvest,

• Water use efficiency is greatest during cool to moderate temperatures, especially during spring.

6. Irrigation timingDue to the above described reasons, alfalfa responds to irrigation very well, 14-16 t hay per hectare can be obtained with irrigation. In addition to weather, the yield increasing effect of irrigation also depends on the age of alfalfa. The irrigation of 1st year alfalfa mainly serves the fastest possible strengthening of the plant population. In addition, its yield increasing effect is also significant. The best results can be obtained with the irrigation of the 2nd year alfalfa; therefore, utmost care should be taken about the water replenishment of the 2nd year growth. If the 3rd year alfalfa was irrigated in the preceding years, the population will become thinner. The thinning plant population that is prone to weed infestation should only be irrigated in extremely dry crop years. As a result of irrigation, the yield of each growth becomes more balances in certain years, which has many advantages for farmers.

It is a general observation that irrigation more or less contributes to the faster thinning of the alfalfa plant population. This natural process is partially connection with the “vital performance” of the plants. In the first two years, irrigation increases yield more than twofold. As a result of high yield, the rhizoma performance becomes weak, it does not have enough reserve nutrients which can also be considered faster ageing.

The date of irrigation of alfalfa can be determined in accordance with the reaping schedule. The precipitation in the winter period does not soak the upper 200 cm of the soil every year. The water need of the first growth is not always covered by natural water supply. If the drought in April does not have any effect, it becomes necessary to apply 50-60 mm irrigation water. If April is not dry and windy, one should only irrigate after the first reaping. If the winter precipitation is 200-250 mm or more and the first growth develops adequately, there is no need for irrigation. The second, third and further growths should only be irrigated if the water supply and the amount of precipitation are known. This irrigation schedule results in applying about 220-310 mm extra irrigation water in addition to the yearly precipitation in the Trans-Tisza and the Danube-Tisza mid-region. If the precipitation over the year reaches 800-900 mm, irrigation is not needed, but it is of fundamental importance that the amount of water (precipitation + irrigation water) which is the basis for reaching high hay yields should be around 500 mm.

Because of its deep, well-developed root system, alfalfa can allow the irrigator to use rainfall efficiently. To maintain the best growing conditions and receive the greatest benefit from rainfall, irrigation applications should not exceed 75-100 mm (when surface irrigation is used) except for a fall or spring irrigation on deep, medium-textured soils. In western Hungary, it is possible to utilize rainfall more effectively if the soil profile is not completely refilled by irrigation. This leaves water-holding capacity in the soil to store rain occurring immediately after irrigation.

For surface irrigation systems using applications of about 50 to 100 mm and 2 to 3 irrigations per cutting will normally be required. Start the first application about five days after cutting and finish the second about five days before cutting. This type of schedule must be adjusted to reflect soil moisture status, crop needs and system capacity. For sprinkler systems, the size of application often will be smaller. Because of the lower application amounts, the irrigation frequency likely will range from three to seven days. However, after crop re-growth has begun to use higher amounts, use up to 75 mm per application if soil infiltration rates will allow, preventing development of shallow root systems (Table 13.).

10.1. táblázat - Table 13. Distribution of the amount of irrigation water in the growing season in the case of using surface and sprinkler irrigation methods (mm/ha)

Applications Timing Surface Sprinkler

1. Irrigation after the 1. cutting 70-80 mm 50-70 mm



CROPS: ALFALFA




Total amount of irrigation water 280-340 mm 220-280 mm

It is suggested that adequate soil moisture (i.e., 80-90% of the field capacity) be maintained in the soil profile to a 100 cm depth at the time of first cutting. Alfalfa will maintain optimum growth when the soil water is maintained between 70 and 50 percent of the available water capacity for the remaining period of the growing season. As long as water remains in this range, there will be little difference in yield and water use. However, for highest yield, the soil water balance in the root zone should not drop below 40 percent of the available water capacity.

Start irrigation before soil water in any part of the field drops below 40 percent of the available water holding capacity (60 percent depletion). From a practical standpoint, and especially for coarse-textured (sandy) soils, start irrigation when 50 percent of the available water capacity has been used. Plant stress can occur when available soil water drops below 50 percent.

Irrigation is not recommended to be started directly after reaping, because the evaporation loss will be high and the relative airless character of the upper soil layer slows down the sprouting of alfalfa. Irrigation can be started once the new growth reaches 10-12 cm plant height on soils of middle to high plasticity or 15 cm on loose soils. After this period, the alfalfa and its water need increase quickly. The plant population provides an almost total coverage on the soil, evaporation is reduced to the minimum and the applied irrigation water is used at a higher level of efficiency.

Just after cutting, the alfalfa plant is most vulnerable to excess water. Irrigating immediately after harvest also may stimulate weed growth. As a general rule, complete irrigation several days before cutting and do not start again until alfalfa re-growth has begun. This full interval may not be possible on soils with low available water-holding capacity or when the irrigation system capacity is limited. During these situations, stop irrigation 2-3 days before the cutting and begin again as soon as hay is removed.

A major consideration when timing irrigation is interference with harvest. Irrigate as close to harvest as possible to meet the peak needs of the crop and have adequate moisture available to start re-growth. Give the soil surface enough time to dry to prevent excess soil compaction during harvest and to prevent hay on the soil surface from absorbing excess water and delaying the drying process. If the surface is too wet at harvest, the soil will be compacted by the harvesting equipment, seriously reducing the soil intake rate for future applications of water.

Scheduling irrigations is complicated by the harvest schedule, which occurs about every 28 to 30 days. Irrigation scheduling is often controlled by the harvest schedule, not by allowable soil moisture depletion. Growers are limited to the choice of irrigating 1-3 x between harvests, depending upon soil type and year. One irrigation between harvests may result in excessive soil moisture depletion between harvests. With three irrigations between harvests, irrigations will occur before the allowable depletion occurs therefore relatively small applications of water are required.

Fall irrigation can be an important management tool on deep, medium-textured soils in the drier alfalfa growing areas. Fall irrigation provides good growing conditions prior to winter dormancy and helps the plant build its reserves in the root system, and gives vigorous spring re-growth. The deeper portion of the soil profile can be refilled in this off-season period because peak water use is not placing a demand on the system capacity. Water placed in the deeper portion of the profile will be available during the peak water use period. When water is applied in the fall, avoid excessive applications, which can cause water to percolate below the root zone or ponding, which, in turn, will cause crop loss.

7. Irrigation scheduling methodsIrrigation management includes deciding when and how much water to apply. The decision must be based on the available irrigation water supply, the available water-holding capacity and intake rate of the soil, the water needs



CROPS: ALFALFAof alfalfa for a given period and the irrigation system capacity. The management objective normally will be to meet the crop water needs to provide for optimum plant growth. The success in meeting crop needs will depend upon the size of the available water supply. The timing of harvest and other time factors also must be considered. Criteria to help determine when to irrigate include soil water monitoring and water use prediction based on climatic data.

8. Crop appearanceThe appearance of alfalfa can indicate soil water status. When adequate water is available, alfalfa usually will be light green. As moisture stress develops, the color darkens. Apply water when the plant has turned dark green, before wilting occurs, otherwise yield and quality will be reduced. Wilting generally will occur when about 25 to 30 percent of the available water capacity remains in the root zone. Drought-stressed alfalfa matures earlier, thus forage quality will peak earlier and degrade more rapidly than under normal conditions.

9. Calendar methodTo determine a calendar schedule, use an estimated water-use rate and soil water-holding capacity. For example, if the average water use rate is 8.9 mm per day and the available water capacity of a silt loam chernozem soil is 185 mm per m, the following schedule could be developed (Table 14.):

Do not overlook weather conditions, irrigation system capacity, and other factors when using either the proportion of growth or calendar schedule. Without consideration of all the factors involved, it will be easy to over- or under-irrigate.

10.2. táblázat - Table 14. Alfalfa irrigation scheduling with calendar method

Schedule for calendar-date method

Effective root zone 90 cm

Available water capacity at 90 cm depth 185 x 0.9 = 166.5 mm

Minimum allowable balance 35%

Available water at min. allowable balance 0.35 x 166.5 = 58.3 mm

Usable water 185 – 58.3 = 126.7 mm

System application efficiency 85%

Gross irrigation application 126.7 ÷ 0.85 = 149.1 mm

Irrigation frequency 149.1 ÷ 8.9 = 16.8 days

10. Crop water use and monitoring soil water statusDaily weather data can be used to estimate crop wateruse. Estimated crop water use can be calculated using datafrom a series of automated weather stations across Hungary.

Crop water use estimates can help calculate the currentsoil water status of a given field. One of the oldest proceduresis called “checkbook irrigation management.” The soil acts asa “bank” or reservoir to store water for crop uptake. Rain andirrigation are deposits to the bank and the crop water use is awithdrawal. Like a checking account, a weekly (or any other interval) balance of these deposits and withdrawals will give the amount of water remaining in the root zone.



CROPS: ALFALFAMonitoring soil water is critical for an effective irrigation management, so you know when to irrigate and how much water to apply. Several methods can be used. The calculated soil water balance can be checked periodically by using some type of soil water monitoring. Measuring the irrigation water applied to a field will improve the accuracy of the soil water balance calculation.

The irrigator may install soilwater resistance sensor blocks at various depths and field locations and determine soil water with a portable electric meter. The electric meters are good for medium- to finetextured soils, and they eliminate guesswork while saving time and effort. A tensiometer may be used for sandy soils. These are easier to read and provide adequate information for most scheduling, but theylack the range to cover the soilwater-availability status of all soils.

Resistance sensor blocksmeasure soil matric potential, which is an indication of the energy plants must exert to extract water from soil. The soil matric potential reading at which irrigation is necessary depends on soil texture (seeTable 6). Sandy soils retain far less water than soils with a high clay, silt, or organic matter content, so irrigation on sandy soils should occur more frequently and at a lower soil matric potential value (negative sign of the matric potential is omitted).

The matric potential reading will increase as the soil becomes drier. After the field is irrigated, the matric potential readings typically return to lower values (i.e., 0 to 10 kPa). These wetting and drying cycles continue throughout the season as the crop is irrigated and the soil dries with crop water use and surface soil evaporation.

The key to proper irrigation management using soil water sensors is to monitor the sensors regularly, track the soil water level, and irrigate when the kilopascal (1 kPa = 1 cbar) readings are in the desired range for your soil type (Table 15.). Irrigating when the soil water readings exceed the desired range may result in crop stress and yield loss. Irrigation before the readings reach the desired range may result in excessive irrigation, water wastage or runoff.

10.3. táblázat - Table 15. Suggested values of soil matric potential at which irrigations should be applied for alfalfa for different soil types (Orloff et al., 2003)

Soil Type Moisture Reading (centibars)

Sand or loamy sand 40-50*

Sandy loam 50-70

Loam 60-90

Clay loam or clay 90-120

*Caution: Soil moisture sensors may not be useful for very sandy soils with extremely low water holding capacity, as the sensors may not respond quickly enough to the rapid decline in soil moisture.Note: These values were based on 50% depletion of available soil moisture for different soil types.

11. Evaluation of alfalfa irrigation methodsSurface Irrigation

Surface systems usually have a large irrigation capacity. Irrigating alfalfa with a surface irrigation system often involves the use of border strips. These strips are long, narrow areas that are contained between low dikes along either side. The width is generally sized to accommodate the harvesting equipmentefficiently. They are usually graded to a uniform grade of 0.3 to 3 percent along the length but are level across the slope. Water is rapidly introduced along the upper end of the strip and flows to the lower end. The alfalfa stand provides roughness to slow the water, help it spread across the strip, and prevent erosion. If properly designed, little runoff is produced, and the application efficiency is 75 to 85 percent. Because wind and low humidity have only minor effects, this system is relatively easy to manage.

Many irrigators who surface irrigate other crops also utilize corrugations and bedded-furrows for alfalfa, even



CROPS: ALFALFAthough irrigation control is less precise than a well-designed border system. Corrugations are shallow furrows that help direct water flow in a certaindirection. However, they are tooshallow to prevent overtopping ifthe flow is too great and are ofteneasily obstructed. Corrugations arean inexpensive method of gaininglimited irrigation control. Furrows,or bedded furrows, offer additionalcontrol of the water through thesystem, but they create a rough surfaceto contend with at harvest.

Sprinkler systems

Sprinkler systems irrigatethe vast majority of crops and are an effective method toapply irrigation water efficientlyand uniformly for a wide varietyof field topography and soil types.The major difficulty of irrigatingalfalfa with center pivot systems isrelated to having dry soil surfacesfor harvest and encouragement ofweed germination with irrigationby center application before alfalfaregrowth reaches full cover. Harvestinginterruption of irrigationalso has an effect on the irrigationcapacity for the field.

Subsurface Drip Irrigation

Alfalfa needs plenty of waterafter each cutting to start regrowth.Subsurface drip irrigation (SDI)systems allow continuous irrigationright after harvest to encouragerapid regrowth and do not requireirrigation suspension prior to harvestto allow for dry soil. Accordingto studies done in USA (California,Texas), SDI has shown increased alfalfayield when compared to furrowirrigation. Findings for SDIsuggest it is a feasible technologyand economically competitivefor small or odd-shaped fieldswhen sprinklers are not feasible.When surface wetting is reduced,evaporation loss and weedgermination is also reduced. SDIgreatly lessens the opportunityfor deep percolation and surfaceevaporation loss. Research studies indicate that it is possibleto save 25 percent of total waterdiverted in a season by using SDIcompared to sprinklers. However,SDI systems, when used on permanentcrops like alfalfa, may makeadditional management concerns,such as increased rodent pressure (Table 16.).

12. Water management impact on diseasesIrrigation causes airless conditions in the soil, which last for a shorter or longer period, eliciting the proliferation of pathogen fungi (Fusarium and Verticillium) and plant disease. This fact, as the unwanted attribute of irrigation, also contributes to the faster thinning of the population. Furthermore, trampling caused by more frequent reaping also accelerates these processes. The unfavourable effect of irrigation was attempted to be reduced also by breeding Verticillium resistant and tolerant varieties.

Table 17 summarizes the diseases, pathogens, symptoms, and recommended controls for alfalfa diseases associated with irrigation (moist environment).

10.4. táblázat - Table 16. Evaluation of alfalfa irrigation methods (Source: own editing on the basis of Alam and Rogers, 2009)

Surface Sprinkler Subsurface Drip Irrigation

Large irrigation capacity, but large quantity of water may pond on the soil surface during irrigation

Effective method to apply irrigation water efficiently and uniformly for a wide variety of soil types

Allow continuous irrigation right after harvest to encourage rapid regrowth

If properly designed, little runoff is produced

Major difficulties: dry soil surfaces for harvest and encouragement of weed germination before alfalfa regrowth reaches full cover

Do not require irrigation suspension prior to harvest to allow for dry soil

Application efficiency is 75 to 85% Harvesting interruption of irrigation Surface wetting, evaporation loss and weed germination is reduced

Wind and low humidity have minor effects

Saving of 25% of total water diverted in a season compared to sprinklers



CROPS: ALFALFA

Relatively easy to manage Additional management concerns: increased rodent pressure

10.3. ábra - Table 17. Water management impact on diseases (Source: modified from Alfalfa Production Handbook, C-683, 1998)

13. Summary• Alfalfa can be grown on a variety of soils, but deep, uniform, well-drained, medium-textured soils are easiest

to manage. Most irrigation systems can be used on alfalfa if designed properly for the site.

• Seasonal water use in Hungary ranges from 800 to 850 mm, including precipitation, depending on location and weather conditions. The peak daily water use rate will normally range from 7.6 to 8.9 mm July and August.

• For optimum growth, maintain soil water content in the effective root zone between 50 to 70% of the available water holding capacity.

• Manage irrigations so that the soil is not excessively wet at harvest. Excess water causes diseases, reduced growth rate, and loss of stand.

• For effective irrigation management, monitor soil water status and couple this information with crop water needs and system capacity.


11. fejezet - 11. IRRIGATION MANAGEMENT OF MAIN CROPS: GREEN PEA, SWEET CORN1. GREEN PEA1.1. Climate requirementsPhotoperiod. The development and the various development phases of pea are much more sensitive to the given part of the day and the light and heat circumstances than other field crops in general. Usually, pea is a long-day plant, but it also has day-neutral varieties. In order for the stem to properly lengthen, and for pea to reach the optimum vegetative development stage, the plant needs short day duration. For this reason, pea prefers the early coming of spring around late February – early March, so that it can have even less than 12 hours or usually around 12 hours of illumination. In the crop years when the sowing of pea is protracted to even the second half of April and the initial weather is not cold and cloudy enough, pea remains dwarf. Therefore, pea is capable of high yields only if the conditions of strong initial vegetative growth and the development of as many yield-forming factors as possible are provided in addition to other favourable circumstances.

Effective heat sum. The growing season of pea is determined by its effective heat sum demand in addition to several other factors, independently of whether the crop receives this heat sum in a longer or shorter period. Depending on the given variety, the effective heat sum or heat unit demand is usually between 630-940 °C from sowing to green ripening. The effective heat sum is calculated by summing the daily effective heat units from sowing to harvesting in a way that 4.4 °C is deducted from the everyday mean heat. The assimilation heat threshold value of pea is 4.4 °C.

1.2. Seasonal water needsThe highest yield of Pisum sativum (L.) can be obtained in the temperate zone. In its different phenophases, pea reacts to the lighting period, the intensity of light, as well as the extremities of temperature and precipitation sensitively.

Pea is an annual cool-season legume crop that is well-adapted to Hungarian continental climate. Optimal pea yields can be obtained if the crop is seeded early in the spring in order to flower before the hot summer weather conditions. A pea crop uses water for growth and cooling purposes. The water requirement or evapotranspiration (ET) for pea depends on variety, plant architecture, growth habit, growth stage, canopy density, climatic conditions, and irrigation and crop management.

Pea grown under optimal conditions (well-fertilized, adequately inoculated, well-irrigated, well-drained soils, pest-free stand, and uniform and optimum canopy) requires from 380 to 400 mm of water per growing season in Hungary.

Average pea water use ranges from 0.1 mm per day soon after emergence to nearly 6 mm per day during the flowering and early pod development stages (Figure 31).

11.1. ábra - Figure 31. Daily water use of greenpea during the growing season (Modified from Efetha, 2011)



CROPS: GREEN PEA, SWEET CORN

Of the critical climatic elements of pea, agrotechnical solutions affect only water supply to a lesser extent. Every crop whose harvesting is due early to mid summer can produce yield more safely if soils are optimally supplied with water from late summer. This is especially true in the case of soils with deep fertile layer and high water intake capacity where pea is able to use the stored water stocks of the soil during drought periods. In the years, when precipitation has a favourable distribution, i.e., there is enough precipitation in the autumn months and in the winter period and there is average amounts of rainfall in each month during the growing season (35-38 mm in March, 40-46 mm in April, 50-55 mm in May and 60-65 mm in June), pea is able to continuously cover its water demand even on weaker soils. Unfortunately, this type of rainfall distribution is rare due to the continental climate of Hungary and pea struggles with periodical water shortage in most years.

During germination, the pea sowing seed needs large amounts of water in order to saturate seeds with water and to develop a deeper root system associated with powerful germination. However, too much moisture in the soil is harmful. Drought at young age also sets back vegetative growth and pea remains short. Water supply in the period of flowering could become critical in the case of precipitation shortage, especially if the soil could not store enough water in the previous periods. The yield of varieties of different growing seasons significantly changes depending on whether the rainy period after a dry period falls within the flowering of shorter or longer growing season varieties.

The water need of crops decreases in the second half of the growing season. In the case of pea, water abundance at the time of ripening is especially harmful as is increases the infection of the various fungal diseases of the pod and the pea, protracts ripening and decreases the germinative ability of pea.

1.3. Soil requirementsThe most preferred soils for pea production – also in European circumstances – are calcic or calcareous chernozem soil formed on loess, as they cover the needs of pea (good water management, structuredness, proper chalk and humus content, neutral or slightly alkaline character 6.5-8 pH etc.) the most.

Sandy loam soils are also suitable for pea production, providing high yields can in the case of favourable crop year (i.e. covering the water, light and heat demands of pea).

Acidic brown forest soils are not suitable for pea production due to their shortage of chalk, high plasticity and low pH. The least suitable soils for pea production are alkaline soils, cold clay textured meadow soils with high groundwater level and low humus content sandy soils with unfavourable heat management.

The low proportion of the sowing area of pea and its production risk due to weather, as well as the uneconomical of production make it necessary to produce pea on better soils.

1.4. Rooting depth and available water




Typically, pea roots grow to an effective water extraction depth of 70 cm in a well-developed soil. Root distribution is concentrated near the surface; hence, pea obtains 70 per cent of its seasonal water from the upper 35 cm of the active root zone of 70 cm. The active root zone changes from a few millimetres at emergence to a maximum depth of 70 cm at the flowering growth stage (Figure 32).

11.2. ábra - Figure 32. Greenpea root zone

The irrigation amounts required to replenish the root zone once the allowable soil water depletion level is reached will vary with soil texture and growth stage, as indicated in Table 18.

11.3. ábra - Table 18. Soil texture-based estimation of total available water and net water amounts per irrigation event during the greenpea growing season (Modified from Efetha, 2011)

1available soil water, 2field capacity, 3with low (2%) organic matter, 4with high (3%) organic matter

1.5. Irrigation managementThe goal of irrigation management is to use available irrigation water effectively in managing and controlling the soil moisture environment of crops to do three things: promote the desired crop response, minimize soil degradation, and protect water quality. Proper irrigation management requires a good understanding of a number




of factors:

• soil fertility (crop nutritional requirements) ,

• soil-water-plant relationships,

• crop type,

• crop sensitivity to water stress,

• crop growth stages,

• availability of a water supply,

• climatic factors that affect crop water use such as rainfall, temperature, humidity, wind, and net radiation,

• irrigation system capabilities and limitations.

1.6. Irrigation scheduling strategiesA workable and efficient irrigation management strategy should be crop-specific. Crop-specific irrigation management strategies mean available water is used efficiently to meet a specific crop’s water requirements for maximum water productivity.

Generally, the goal is to ensure that water is available at germination and in early development by applying light, frequent irrigations (if there is no rainfall). This method promotes vigorous growth, replenishes and increases available soil water content in the entire root zone during the pre-flowering growth stages. Such a strategy will allow modern sprinkler irrigation systems to keep up to crop demand during the peak water use period, which typically occurs during the flowering and fruit-formation growth stages.

Crop-specific irrigation management strategies are usually applied to adjust for the following differences among crops:

• effective root zones,

• sensitivity to water stress,

• types (cool versus warm-season),

• vulnerability to diseases at various,

• crop growth stages,

• response to soil fertility levels,

• plant population/densities,

• physiologic maturity (timing of last irrigation),

• potential income.

The irrigation of pea has special importance. Farms that have irrigation opportunities should facilitate pea irrigation in order to secure the outstanding profitability of pea without any risk. Depending on the water storage capacity of the soil and the given crop year, 80-120 mm irrigation water has to be applied in years when there is a need for water supplementation.

1.7. Vegetative growthIn very dry crop years when soils dry out to the point that the precipitation in the winter period does not make it possible to saturate soils with water, 20-25 mm sprouting irrigation needs to be applied on pea after sowing. Similarly, 15-20 mm irrigation dose needs to be used in areas alongside the Danube with gravelled subsoil. If




there is still water shortage another 40-50 mm irrigation water should be applied in the early vegetative development stage.

Effective pea irrigation scheduling uses soil water levels in the root zone as a measure for starting and stopping irrigations. Adequate soil water is critical for pea during the emergence, vegetative, flowering, and pod development growth stages. Ideally, soil water content in the 0 to 40-cm depth should be greater than 60 per cent of available at planting.

Pea needs to have water for germination and root development during the early stages of growth. Inadequate soil water in these early growth stages results in reduced plant populations and biomass yield, which, in turn, reduce final seed yield.

A vigorous pea stand can result if available soil moisture is not depleted to less than 60 per cent in the 40-cm root zone during the vegetative growth stages. Managing soil water in a 40-cm root zone translates to light and frequent irrigation applications during the vegetative growth stages.

Irrigation water applied during vegetative growth should meet crop water requirements and build up soil water to near field capacity in the 40 to 70-cm zone for later crop use during the peak water use period when flowering (including pod set) and yield formation (pod development and pod filling) are occurring.

Flowering and yield formation

In general, pea is most sensitive to inadequate soil water during the flowering and yield formation growth stages. Inadequate soil water during these stages can drastically reduce pod and seed set, resulting from flower and pod abortions.

Pea roots reach maximum extension at the flowering growth stage. To ensure that soil water is adequate throughout the root zone, the monitoring depth of the root zone should be increased from 40 cm to 70 cm at first flower appearance, and soil water should not be depleted to less than 60 per cent of available. Increasing the irrigation management root zone from 40 cm to 70 cm at the flowering growth stage requires less frequent and larger irrigation volumes and results in increased water availability to the mature pea roots. This increased time between irrigations keeps the soil surface dry, discouraging the growth of fungal diseases. Irrigation may be stopped when the pods start to ripen.

Pea needs considerable amount of water also at the flowering and the pod development stage. In this period, pea needs to be irrigated 2-3 times, applying 20-25 mm irrigation water. In order to prevent protracted flowering, there is no irrigation during flowering.

Small irrigation water doses should be applied so that both harvesting and ripening can be delayed successfully. In fields where pea was sown at the same time, the population irrigated with small doses, thereby providing a steady application with a linear irrigation system ripened 5-6 days later than in that of the population, which was irrigated with a self-propelled system.

Pea yield can be made steady and more balanced in most years on clay soils with deep fertile layer by using the necessary seasonal doses. Using higher seasonal doses becomes necessary on these soils only in extremely dry crop years.

The availability of sufficient, good quality water to pea plants during the flowering growth stage increases the number of pods (or marketable pods for fresh markets) and seeds per pod, whereas water availability during the pod development growth stage increases the pod and seed weights.

2. SWEET CORN2.1. Climate requirementsSweet corn is a warm climate plant, which needs about 80 to 120 frost-free days from sowing to harvest. It needs warm, sunny weather. Crops should be planted once the likelihood of frosts is over and soil temperature is above 12°C. The temperatures for optimum germination should be above 18°C. For optimum growth and quality, the temperature range is from 24°C to 30°C.




The kernels will not set, especially on the tip of the cobs, if conditions are hot or cold or dry and windy at silking. Hot conditions hasten maturity, the sugar in the kernels turns to starch, and quality deteriorates rapidly.

2.2. Soil requirementsA wide variety of soils is suitable. Sweet corn plants will grow in a variety of soil types, but growth is best in fertile, loamy, well-drained soils of pH 5.8 to 7.0. Water-logged or poorly drained soils are to be avoided, as root decay and resulting poor plant growth may result.

The detailed description of suitable soils for corn production is provided in Chapter 12 (Irrigation management of main crops: corn, corn seed).

2.3. Rooting DepthSweet corn has a relatively shallow rooting depth compared to field corn (Figure 33). Most literature suggests that under irrigation, only soil moisture in the top 45 to 60 cm of the rooting zone should be managed. If the soil is shallower or a restrictive layer prevents root growth, the root zone to be managed must be reduced.

11.4. ábra - Figure 33. Sweet corn rooting depth

2.4. Crop water useWater use by the crop is referred to as evapotranspiration (ET). Sweet corn will use 100 to 150 mm less total water than field corn in a season, but generally will use similar daily amounts for the same conditions. Daily ET is dependent on several factors such as

• Climate. More water is used during hot, dry, and windy weather.

• Length of growing season. Long season varieties (95 to 100 days) will use more water than short season varieties.

• Sage of growth. As corn approaches tassel formation and silking, its water use rises dramatically.

• Irrigation practices. The more frequently corn is irrigated, the higher the rate of evapotranspiration. This is due primarily to excessive water evaporation losses from soil surface and foliage. The difference in evaporation loss may be large under sprinkler systems or quite small with furrow systems.

• Stand. A proper stand uses water most efficiently. In the case of poor stands, excessive water loss from bare soil may occur.

• Fertility. The best ratio of production to water used is obtained under moderate, but adequate fertility. Nitrogen is the most important element in this regard. Under less than optimum fertility, water use per unit of gain is excessive.




Table 19, gives estimated daily crop water use in mm for different corn growth stages and several maximum daily air temperature ranges. The greatest daily water use will usually occur from tassel to harvest. It is common for sweet corn to use 6.4 mm per day or more for several days. To keep up with this use, your irrigation system must have a similar capability. For sandy soils, a system capacity of 6.4 mm or greater per day is generally recommended.

11.5. ábra - Table 19. Estimated daily cropwater use of sweet corn (Source: Fritz et al., 2010)

The most critical periods of water need in sweet corn occur during the tasseling stage, silking stage, and ear fill. Even a 3- to 4-day period of water stress during these stages can result in a 60% yield reduction.

2.5. Irrigation ManagementWater management of irrigated sweet corn is an essential production practice to produce optimum yields and quality ears. Yield and quality of ears are significantly reduced if moisture stress occurs during tasseling, silking, and kernel fill. Short periods of moisture stress earlier in crop development usually will not affect yield unless poor germination occurs. However, it may delay harvest date. To manage the soil’s moisture effectively, a regular in-field soil/water monitoring program should be established to assist in irrigation scheduling.

Establishment of an effective irrigation scheduling program involves being knowledgeable of several factors and then putting them into practice. The following discussion briefly outlines those factors.

2.6. Irrigation TimingGenerally, optimum sweet corn growth will occur if the soil moisture level is maintained at about 85 percent of the available water capacity, although symptoms of moisture stress usually do not appear until the soil moisture has been reduced to 40-50 percent of capacity. Cycles of extreme wet versus dry conditions should be avoided as it may reduce ear quality. Sweet corn is most sensitive to moisture stress during pollination and ear formation. The most practical approach is to irrigate by crop growth stage.

2.7. Vegetative growthIrrigation start-up should generally occur when the soil moisture level is between a 20 mm deficit and 60 percent of field capacity. During the critical growth stages, keep the soil moisture as high as possible at all times. Irrigate before planting if moisture is low. At germination time it is also important to start out with a full profile, but then allow the soil to dry down to possibly 50-60 percent of field capacity up to the 10-11 leaf stage to ensure a rapid and complete root development. Corn can tolerate some water stress during this growth stage without serious impact on yield and quality. If irrigation system capacity is restricted, one can maintain soil moisture at about 40-50% of field capacity. Sweet corn needs one to two irrigations between planting and tassel formation, depending on the soil type. Timing of irrigation may also be influenced by other factors, such as nitrogen application, insecticide spraying, disease suppression, forecasted rain, and harvesting.

2.8. Generative growth




Corn needs two to three irrigations during tasseling and silking. Raise soil moisture to 60% ten to twelve days before tasseling and to 70% during pollination. Take measurements at about the 25 to 30 cm depth. After pollination, corn may need one to two irrigations. The soil moisture percentage can fall off to about 60%.

3. SummaryUsing suitable irrigation strategies with greenpea can mean a healthy crop with high yield and quality potential. In addition to ensuring that the pea crop is well-fertilized and well-protected from pests, growers are encouraged to properly manage irrigation by regularly monitoring soil water to ensure that the availability of water does not become a limiting factor in producing a high-yielding pea crop.

Applying irrigation just before the available soil water is depleted to 60% at any pea growth stage and replenishing available soil water near field capacity in appropriate root zones will greatly assist in producing a high-quality and high-yielding pea crop.

Sweet corn requires adequate water to maintain quality and yield. Since product quality is the primary feature by which the crop is marketed, a reduction in quality is not acceptable.

If water is going to be a little short, growers can reduce water applications to some degree early in the growth of the crop. However, it is critical to have sufficient moisture during tasseling and silking. The most critical periods of water need in sweet corn occur during the tasseling, silking and ear fill stage. Even a 3- to 4-day period of water stress during these stages can result in a 60% yield reduction.


12. fejezet - 12. IRRIGATION MANAGEMENT OF MAIN CROPS: CORN, CORN SEED1. CORN1.1. Climate requirementsPhotoperiodism. Maize is originally a short-day plant, but it adapted remarkably well to the long-day circumstances over the centuries. The tropical short-day maize populations develop their vegetative organs for a long time under temperate zone conditions and they only flower late September. The development of the populations, which adapted to the temperate zone long-day conditions is strongly accelerated under tropical and subtropical circumstances, they form little vegetative mass and flower early. If the populations of various growing season length, which were domesticated in the temperate zone are transferred from the 42° to the 46-48° latitude, their growing seasons prolong by 25-35%.

Currently, the high yield potential of maize can be exploited the most at the 42-45° latitude worldwide. The central strip of the European maize belt is along the Po Plain and Krasnodar. The corn belt of the USA in the North American continent falls to the southern part of this strip, while Hungary is in the northern part. The climate of Hungary makes it possible to perform maize production safely only until FAO 500-600 even in the southern part of the country.

Temperature. Temperature is the most fundamental requirement of the production of maize. Maize is capable of the highest yields where the mean temperature of the hottest summer months is between 21-27 °C. In the Hungarian maize production areas, the monthly mean temperature values (June >19 °C, July >21 °C, August >20 °C) hardly reach the lower threshold value of the optimal range (19 °C). The most favourable temperature between tasseling and lactic ripeness would be between 24-26 °C. In the ripening phase, maize is less sensitive to temperature (>15 °C). In the maize production regions of Hungary, temperature is not below the physiological threshold value of maize, except for extreme fluctuations. There is great temperature fluctuation in the spring and autumn and it is not always favourable for maize development. Late warming up protracts sowing and emergence. After emergence, the frequency of cold weather is high in the spring, when the assimilation activity of maize is temporarily on hold and maize is ripened due to the oxidation loss.

The temperature of the Hungarian climate mainly affects the length of the period between emergence and tasseling, which also limits the ripening period of maize, while the autumn weather is mostly dry and warm, which is favourable for maize ripening and the water loss of grains. It has a lower probability that the autumn will become cold and wet, thereby inhibiting the reduction of the grain moisture of maize.

1.2. Seasonal water useSeasonal water use is affected by climatic conditions, relative maturity range, soil fertility, water availability and the interaction of these factors. Although the total amount of water used by corn will vary from season to season and location to location, it will generally follow the pattern dictated by seasonal trends in weather variables and corn development. The smooth curve in Figure 34 (Curve A) illustrates the long-term average water use pattern for corn. The jagged curve (Curve B) illustrates the fluctuation possible in daily ET values for an individual year.

12.1. ábra - Figure 34. Water use of corn during the growing season



CROPS: CORN, CORN SEED

(Source: modified from Kranz et al., 2008)

Thus, irrigation managers must be familiar with the long-term trend but more importantly be able to determine what the daily ET was over the last few days. Knowledge of the long-term trend and actual daily crop water use rates are critical to determining when to irrigate and how much water to apply.

Population also effects water use by influencing the amount of leaf surface that is available to capture solar radiation, which is the energy source for crop production. Leaf Area Index (LAI) is a measure of the leaf surface area relative to the ground surface. It takes an LAI of about 2.7 to fully capture all incoming energy (Figure 35). If LAI is less than this full-cover value, then less water use will occur, as long as the ground surface remains dry. More plants in a field may provide larger LAI for full sunlight capture and more effective use of water. Since crop yield is proportional to consumptive water use or evapotranspiration (ET), it is generally advisable to adjust plant population for maximum capture of sunlight and effective water use.

12.2. ábra - Figure 35. Effect of plant population (plants/area) on corn leaf area index (LAI)

(Source: Kranz et al., 2008)

Hybrid maturity length can affect water use. These effects are illustrated in Figure 36. Earlier maturity varieties will have less water use, in some cases, as much as 100 to 150 mm less. However, yield is also reduced so the trade-off between water cost, yield and other production factors must be considered when selecting a maturity length.



CROPS: CORN, CORN SEED12.3. ábra - Figure 36. Seasonal water use of different corn maturities

(Source: Kranz et al., 2008), (Author’s note: 1 in. (inch) = 25.4 mm)

ET of corn hybrids for a given maturity lengtharealso influenced by different planting dates. ET is less for earlier planted corn, since more of the growing season occurs in less severe weather conditions. The highest rainfall months are also early, so planting early can help lessen irrigation requirements.

Under Hungarian conditions, water is available to the minimum extent for maize production. Despite the fact that maize as a C4 crop stands out with its heat and drought resistance, it is difficult for this plant to tolerate the extremely drought crop years in Hungary, depending on the water management of the soil and the groundwater level of the subsoil.

Corn grown under optimal conditions requires from 550 to 670 mm of water per growing season in Hungary, depending on both climatic conditions and previously mentioned different agronomic factors. The main water use period of corn range from mid-June to mid-August. Average corn water use ranges from 2 mm per day soon after emergence to nearly 8-9 mm per day during reproductive and early grain filling stages.

Maize belongs to the group of crops, which have high level of water utilisation. Maize uses the available water especially efficiently; it takes up 163-368 kg water from the soil to produce 1 kg dry matter. However, it needs a huge amount of water to produce its high phytomass. Usually, maize is capable of covering its water need from the groundwater at 100-130 cm depth even in relatively dry crop years. The loess ridge soil with deeper groundwater and good water balance is capable of storing around 220-270 mm available moisture in the 150 cm profile, which can cover nearly 40% of the water need of maize during the growing season. If there is less than 100-150 mm available moisture in the soil in the spring, the risk caused by weather increases. The amount of water originating from the condensation of dew is difficult to quantify, since the extent of temperature fluctuation is different. In many cases, the formation of dew could even totally missing in very hot and dry periods, which especially contributes to the extension of drought damage.

The critical development period of maize is during the period of tasseling-silking. The period of large water consumption starts with the shooting, the quick and massive building of the plant’s structure which usually takes place in mid-June. Flowering takes place in the first half of July. The period of grain formation lasts until early August. Therefore, the main water consumption period of maize is between mid-June and early August.

Unfortunately, in Hungary, this is the period when drought is rather frequent especially in the main maize production areas. It is the opinions of international professionals that maize can only utilise its high yield potential if approx. 100-100 mm water (precipitation or water supplementation) is applied in each of these two months. The favourable constellation of climate elements in the temperate zone, which can be observed in the USA is exceptional; parallel with the higher monthly temperature, which is favourable for maize, precipitation in the growing season also covers the optimal water need of maize (Table 20). In the European maize belt strip – including Hungary –, the warm weather in the summer is usually coupled with a relative water shortage.

12.1. táblázat - Table 20. Multiple decade mean temperature (°C) and precipitation (mm) of the corn belt in the USA (Source: Bocz, 1992)




Month Temperature Precipitation

May 18.3 87.5

June 20.6 82.5

July 22.7 112.0

August 22.7 112.0

Total 394.0

The mean monthly values of the evaporation ability (PET) of the air in the Great Plain: 140 mm in June 170 mm in July and 160 mm in August (Figure 21). Around 75-80% of this value (250 mm) is the real water need of the plant. The moisture stock of the soil is able to cover a certain part of this amount. The missing part has to be covered the precipitation in this period and irrigation together.

The average monthly precipitation sums in the Great Plain are 60 mm in June, 55 mm in July and 45 mm in August. Therefore, the amount of rainfall is 110 mm from mid-June to mid-August, of which a maximum of 80-85 mm can be considered available for the plant. For this reason, if we deduct the “average” 80 mm precipitation from the 250 mm need of this main water consumption period, the soil has to store 170 mm. This amount cannot be found in the 50-60 cm thick upper soil layer, estimations show that the maximum water stock in this layer is 100-110 mm. Therefore, the irrigation of maize is necessary in order to obtain high yield also in a year with average precipitation.

12.4. ábra - Figure 21. Average monthly PET and rainfall values during the corn growing season (Debrecen, 1980-2010)

1.3. Soil requirementsThe high water need, drought resistance, nutrient need and eventually high and steady yield of maize can mainly reached in deep, humus-rich, medium plasticity clay soils. The optimum water-air proportion and the proper warming up needed for the development of maize and the formation of its root system are provided by clay soils. The largest area proportion and the highest and most steady yield of maize could always be obtained on chernozem formed on loess ridge and meadow chernozem soils in the past as well. Maize is produced worldwide on better soils, because its ecological sensitivity is much higher than that of wheat.



CROPS: CORN, CORN SEEDChernozem soils with good water management and deep groundwater level make it possible for roots to access water 2-3 m deep in the winter period, thereby surviving the periodically occurring shorter or longer drought periods.

In the majority of meadow chernozem soils, the groundwater level is above 2.5 m. Maize can be produced the most steadily in these areas. During the crop years when the groundwater level is around 1 m until the middle of the growing season, maize yield is similar to when irrigation is applied.

Furthermore, brown forest soils and chernozem brown forest soils, meadow alluvial soils, meadow soils with arranged water conduction and bog meadow soils are also suitable for maize production. Of cereals, maize production has the highest specific cost; therefore, the proper selection of soils also contributes to reaching the higher and more steady yield of maize.

The extremely weak sandy soils, soils with shallow fertile layer and waterlogged soils are not suitable for maize production at all. Apart from the listed soils, maize can also be produced on other soils in Hungary. However, maize production on soils with weak water and nutrient management is more risky. Alkaline soils also belong to this group. On alkaline soils with better productivity, only the production of early maize varieties can be successful.

Soil pH. Maize tolerates a rather wide soil pH (5.5-8 pH). The pH of soils most suitable for maize production is between 6.6-7.5. The Ca supply of maize production soils and the maintenance of this supply have to be provided continuously in order to increase the nutrient supply ability of soils.

1.4. Rooting characteristics and irrigationAs regards irrigation, a few fundamental factors have to be considered. The fibrous root system of maize is usually shallow rooted. It is not without a reason that this plant was referred to as “root crop on which farmyard manure was applied”, i.e. a plant, which needed optimum circumstances. Hybrids with the greatest vitality somewhat changed this fact, but the basic characteristic of the species remained intact. Therefore, one can draw the conclusion that the majority of the root system of maize is located in the upper, cultivated layer of the soil and it takes up the majority of its nutrient from there; therefore, this layer has to be constantly kept damp with irrigation.

At the same time, the root system of maize is especially sensitive to anaerobic circumstances. The bottom leaves become red even as a result of a short period of over-irrigation. Therefore, over-irrigation has to be avoided by all means, as maize is rather sensitive in this aspect.

Corn is a relatively deep-rooted (150 to 180 cm) crop but only the top 75 to 100 cm of the root zone is usually monitored for irrigation management. In a uniformly wetted profile, 70 percent of the water and nutrients are removed from the upper half of the root zone. Thus, when monitoring the top 75 to 100 cm, at least 80 percent of the active root zone is managed.

Corn does not extract water uniformly throughout its rooting depth. Generally, more water is extracted from shallow depths and less from deeper depths. If water is applied to the soil surface, the typical extraction pattern follows the 4-3-2-1 rule: 40 percent of the water comes from the top 1/4 of the root zone, 30 percent comes from the second 1/4 and so on. The 4-3-2-1 rule is illustrated in Figure 22.

Most of the roots are in the upper portion of the root zone and roots differentially remove water from the soil. The easiest water is removed first and the more difficult later. Therefore, if one zone is wet and another is drier, the plant will extract more water from the wetter zone. Research has shown that at least half of the root system can supply all of the necessary water, if the soil water content is high enough. As a consequence, soil water in the managed upper zone is most important and water at deeper depths may not be significantly used.

The soil water below the managed root zone should be viewed as a marginal insurance supply. Some portion of the midseason needs can be taken from this source but the rate of removal will be slow and the amount will not be great. The time to use this deeper supply is late in the season when the use rate is low and the consequences of soil water stress are also low.

12.5. ábra - Figure 22. Root zone soil water extraction and plant root development patterns




(Source: Kranz et al., 2008)

1.5. Irrigation SchedulingIrrigation scheduling should be used to determine exactly when to irrigate and how much water to apply. Scheduling can take many forms: calendar date, plant growth stage, crop condition, soil water status, and scheduling using evapotranspiration (ET).

Scheduling using calendar date or plant conditions does not work well in Hungary. The weather is highly variable and waiting for the crop to show signs of wilt means that it is too late to prevent damage, particularly during the reproductive period. Waiting for the crop to wilt before irrigation is too late, and corn shows few other obvious signs of water stress. Watching for stress signs in corn is the poorest of methods for scheduling. The damage is done before the stress signs are obvious enough to prevent yield-limiting water stress.

Scheduling using plant growth stage works well on medium and fine textured soils or on organic soils. Unless adequate rainfall is received, water should be applied one week before silking and every week thereafter until dent occurs. Unfortunately, plant growth stage does not work as well on sandy soils with low capacity irrigation systems because crop damage can occur before there is enough time to apply adequate water.

Monitoring soil water is a safe scheduling method with universal application. Soil water may be measured periodically using soil water blocks, tensiometers. Tensiometers are easiest to read, but are only meaningful in sandy soils. Soil water blocks will work in any soil, but for the blocks takes time to place and must be read with an electric meter attached to wires that lead from each block. Several sites in each field should be monitored and the evaluations must be made frequently enough to start irrigations on time.

Scheduling can also be done using crop water use or ET calculations based on temperature and rainfall. Making use of estimated water use rates using a checkbook type routine is an excellent method of determining when to irrigate. A soil water estimate is necessary at the start of the scheduling period for each field. This soil water measurement is treated like money in the bank. Daily use amounts are deductions and rainfall and irrigation amounts are deposits. This way the amount of soil water is known at all times. Observing the trend in values can help growers anticipate precisely when to irrigate. ET-based irrigation software programs are available to calculate water use rates from weather data. It is recommended to use ET based scheduling or monitor soil water on a regular basis or some combination of both.

By knowing soil water capacity, the current soil moisture status, and crop use, precise amounts of water can be applied so that limited moisture supplies are not wasted and crop needs are met. This is where scheduling can be a real asset. Scheduling will indicate when the irrigation system can be shut down. Allowing the irrigation system to run continuously during the bulk of the season is a common but costly procedure. In a growing season with averaged precipitation, rainfall will often allow soil water storage to catch up with crop demand. Without scheduling, the grower is never sure when these periods occur and may be afraid to shut the system down or



CROPS: CORN, CORN SEEDmay fail to restart the irrigation system in time to meet a period of peak water demand during a long dry spell.

1.6. Irrigation management by growth stageGermination and Seedling Stage (0 to 45 days after planting)

Only a very small amount of soil water is necessary to germinate the seed, but adequate water in the top 30 to 45 cm of soil is essential to produce strong seedlings. On medium to fine textured soils or on organic soils, this early season water requirement is normally supplied by rainfall. On light textured, sandy soils, irrigation may be required to germinate the seed and continue proper development. Sands hold little water, so a physiological drought may occur at any time where soil water storage is limited.

Rapid growth stage (14 to 45 days after planting)

During this period, the water use rate is increasing rapidly and some wilting in the late afternoon may be tolerated without harm if the plant regains its turgor by early morning. Available soil water can be depleted by 70 percent of capacity before yield losses occur. On medium and fine textured soils or organic soils, irrigation is seldom required during this period. On sandy soils in the coastal plain, some irrigation is usually necessary in the middle to late part of this growth period.

Reproductive stage (1 week before silking to 2 weeks after the tassel appears)

This is the most critical period for corn. The water use rate is near its high point. If the weather is hot, the plants need plenty of water to keep wilting to a minimum. Holding the soil water storage capacity in the top 20 to 30 percent of its available range is important to stay ahead of water depletion during a prolonged period of drought. On all types of soils in Hungary, it is critical that they be near soil water capacity at the beginning of this period. On sandy soils, an irrigation one week before silking will, most likely, need to be followed up with supplemental applications of water every 2 to 3 days depending on the rainfall received. On low capacity systems or if the grower is using a traveling gun or cable-tow machine, water should be applied throughout this period whenever a rainfall event has not occurred for 3 days.

Grain fill (2 weeks after silking to black layer)

While the corn plant is more stress resistant during this period than it was during the reproductive period, adequate water is still necessary to complete kernel development. Holding soil water in the upper 50 percent of the soil availability range until dent occurs is recommended. Following dent, soil water availability can fall to the 20 to 30 percent range without danger of hurting yield. Medium and fine textured soils and organic soils may require a single irrigation during this period depending on the amount of rainfall received. On sandy soils, the corn crop will most likely need to be irrigated at least once or twice.

In summary, the amount of soil water in the root zone should be viewed as an insurance supply. The time to rely on this insurance is when the rate of removal is slow and rainfall is adequate. This means that the time to use the soil supply is either early or late in the growing period when the use rate is low and the consequences of soil water stress on yield are also low. Irrigation should be considered the primary source of water during the reproductive stage and early grain fill stage.

1.7. Determining the last irrigation for cornDetermining the last irrigation for corn should use the „milk layer” or „milk line” as the criterion for estimating days to maturity. The „milk layer” is defined as the borderline between the bright, clear yellow color of the seed coat outside the hard starch layer (top of kernel) and the milky, dull yellow color of the seed coat outside the dough layer (base of kernel) (Figure 37).

12.6. ábra - Figure 37. Formation of „milk layer” on maize kernel




(Source: http://msucares.com/crops/corn/images/milklinehalf.jpg)

It takes about 20 to 25 days for the milk-line to progress from the top of the kernel (beginning dent stage) to the bottom or base of the kernel (maturity or black layer) where it is attached to the cob. Thus, a final irrigation when the milk-line is halfway down the kernel coincides with 10 to 12 days to maturity. Basically, the coarser the soil texture, the later the last irrigation is needed. The last soil-recharging irrigation of corn grown on silt loam and clay loam soils should occur at about dent stage (20 days to maturity), whereas the last irrigation of corn grown on a sandy soil should occur at full dent stage (about 10 to 12 days to maturity). These guidelines should be considered in conjunction with the time of year that these stages occur, since a greater water use rate between the last irrigation and maturity than that used here (2.5 to 5 mm/day) results in more rapid depletion of soil water between the planned last irrigation and maturity.

1.8. Irrigation scheduling in different climatic regions1.8.1. Humid and Subhumid Region Scheduling

The high probability of precipitation makes scheduling irrigation in humid regions difficult. Chances of over-irrigation are high because of the greater likelihood of summer rains. Rainfall usually supplies the major part of a crop’s water requirement in these regions and should be used to the full extent.

Since the chances are good of rainfall occurring shortly after irrigation, it is advisable not to recharge the complete root zone. This not only reduces irrigation costs, but also minimizes nutrient leaching.

Mobile sprinkler systems, such as traveling guns and center pivots, require an extended period of time to cover the irrigated area. This poses no problem as long as the irrigation cycle is not interrupted by rainfall. Sufficient amounts of rain uniformly recharge the soil to field capacity over the entire irrigated area simultaneously.

If the available soil water is permitted to reach the maximum allowable depetion level following rain, a portion of the field will likely experience considerable water stress before the irrigation cycle is completed.

This problem can be minimized by (1) starting the system when half of allowable depletion occurs and (2) applying half the normal water rate (which should allow the abbreviated cycle to be completed in half the normal time). Such a procedure re-establishes the irrigation cycle without subjecting part of the crop to excessive stress.

1.8.2. Arid and semiarid scheduling

Depending on soil type, expected early precipitation or irrigation at planting normally meets the corn crop’s water demand during the spring in arid and semiarid regions. Then as reserve moisture is used, irrigation becomes the primary means for plant growth.

Scheduling irrigation for corn during high water use periods may seem unnecessary if an irrigator is at best marginally capable of keeping up with crop demands due to either low system capacity or water supply and/or cost restrictions. In such cases, a logical schedule during peak water use is probably to irrigate continually, unless there are rainstorms of sufficient number or intensity for the soil profile to “catch up.” Scheduling will then determine if continued irrigation is needed, should that precipitation occur. In most cases, scheduling in the



CROPS: CORN, CORN SEEDarid areas provides the greatest return during spring and fall.

As the name implies, arid and semiarid regions have low probabilities of precipitation. Therefore, irrigators should plan to fill the soil profile during irrigation rather than leave room for possible rain. It is important to keep ahead of crop demand rather than to risk falling behind trying to leave room for low-probability rainfall. The exception to this occurs in the fall when crop water demand is on its downward trend.

1.9. Irrigation management strategies to conserve waterToday, water supplies are stretched very thin and pumping costs are much higher. In addition, more fields just simply do not have enough water to irrigate the crop fully. With this in mind, water conserving strategies are needed.

1.9.1. Fully Watered Strategy

The Fully Watered management strategy is the traditional Best Management Practice (BMP) that has been around since the 1960’s. It focuses on preventing moisture stress to the crop from planting to maturity by maintaining the plant available soil-water (in the active root zone) between field capacity and 50% depletion. Usually the soil in the root zone is kept 38 to 25 mm below field capacity to allow for rain storage. After the dough stage, the soil is allowed to dry down to 60% depletion.

Management tips

The fully watered strategy is the easiest of the three strategies to manage. Management needs to focus on:

• when to start irrigation for the season,

• limiting irrigation to keeping the soil moisture below field capacity to prevent water from draining below the root zone and to provide space to store in-season rain,

• and when to stop irrigating at the end of the season, so the crop can use enough water to dry the field down to the 60% depletion level before it matures.

1.9.2. Water Miser Strategy

The Water Miser BMP irrigation management strategy focuses on saving water during the less sensitive vegetative growth stages and fully watering during the critical reproductive growth stages. Irrigation is delayed until about two weeks before tassel emergence of the corn, unless soil-water depletion exceeds 70% (in the active root zone). Once the crop reaches the reproductive growth stage, the plant available soil-water is maintained in a range between field capacity and 50% depletion. Usually the soil in the root zone is kept 38 to 25 mm below field capacity to allow for rain storage. After the hard dough stage, the soil is allowed to dry down to 60% depletion.

This irrigation scheduling method is sometimes called a crop growth stage irrigation strategy. Irrigation is limited during the vegetative growth stage while full irrigation management is practiced during the critical reproductive growth stages.

Management tips

Managing a field with the Water Miser BMP strategy requires good soil moisture readings and careful timing. The upper 90 cm of the soil profile should be at or near field capacity in the early part of the growing season so the developing roots can grow in moist soil, thus allowing the stress to come on more gradually. Most fields that were somewhat fully irrigated the previous year will meet this condition even with below normal precipitation. If the field is dry, be very careful not to over stress the corn.

The biggest hazard involved with this strategy is not getting the irrigation started soon enough to avoid excessive stress during the pollination period. If soil water reserves are depleted and something occurs to delay irrigation, severe problems could occur during the pollination period. Also, keep in mind that lower capacity systems need to be started sooner, as compared to higher capacity systems, which can wait to get more of this benefit, but still needs to be started soon enough to get caught up before the reproductive period starts.



CROPS: CORN, CORN SEED1.9.3. Deficit Irrigation Strategy

The deficit irrigation management strategy should only be used if the water supply is short, since it will result in reduced yields. This strategy focuses on correctly timing the application of a restricted quantity of water, both within the growing season as well as over a several year period. The intent is to stabilize yields between years by applying irrigations based on soil-water depletion. The idea is to keep the soil dry enough to significantly reduce ET, but keep it from getting so dry that it substantially lowers the yield potential. Less water will be applied during wetter years, while more will be applied through the drier years, with an average over the years equaling the available quantity of water. The management strategy is to delay the application of water until about 2-weeks before tassel emergence for corn, unless soil-water depletion exceeds 70%.

Once the crop reaches the reproductive growth stage the plant available soil water (in the active root zone) is maintained in a range between 30 and 60% depletion. It is allowed to dry down to 70% depletion after the hard dough stage. The idea is that these depletion numbers should be changed based on the amount of water the producer has to work with. More research is needed to determine guidelines for differing water use levels.

Management tips

The Deficit Irrigation strategy is the most challenging to manage. In fact, it may be as much an art as it is science. The challenge is to keep the crop fairly dry to reduce the ET to the desired level, while preventing an extremely hot, dry few day period from significantly impacting the yield potential. Remember this strategy is intended to lower the plant water use to the amount of water available for the season, but as a consequence the yield will be lowered as well. Also, this strategy does not work with low capacity irrigation system. It only works if the restricted quantity of water can be put on the field quickly and at the right time. If the water supplies are very limited, irrigating less acres or growing a crop that requires less water may be a better option.

2. CORN SEED2.1. Seasonal water useIn drought years, sowing seed production can be steadily performed only with irrigation. The water need of maize during the growing season is 450-500 mm, which is more than the amount of precipitation during the growing season. Under average circumstances, the water shortage is around 100-200 mm that has to be replenished with irrigation. Due to the different regions of Hungary and the different endowments of various fields, there may be major differences from the average. On the one hand, these differences should be taken into consideration when selecting the sowing seed production sites of the various hybrids and also during the planning of irrigation on the other.

The plant population on the sowing seed production plots of the SC and MSC hybrids evaporates less water than TC and DC hybrids. However, they are more sensitive to water shortage. For this reason, these hybrids call for proper water supply conditions. Their population is not closed; therefore, one also has to consider the water loss due to the evaporation of the soil.

2.2. Irrigation managementThe water need of maize from emergence to becoming fertile gradually increases and then starts to decrease. In an average year, natural precipitation covers the water need until around the end of June. After this, the difference has to be made up for with irrigation. There are three different irrigation periods based on water need, precipitation and the phenophases of maize.

1st period: from emergence to two weeks before flowering

Irrigation is needed from emergence to two weeks before flowering in order to replenish the continuously increasing water need. It is also becoming increasingly important to fill up the water stock of the soilpreviously, thereby preparing for the expected water shortage period. It is the experience of drought years that the available irrigation capacity is not enough to apply the necessary amount of irrigation water in the upcoming period when intensive irrigation is needed.

2nd period: from two weeks before flowering until the end of flowering



CROPS: CORN, CORN SEEDThe most critical and also most water needy development phase of the plant population is between tasseling and grain formation. In this period, the water stock of the soil that can be used without irrigation during the flowering period is decreasing. If plants suffer from water shortage in this period, several development processes may be damaged irreversibly, causing a decrease in yield:

• slow and delayed flowering,

• reduced chance of simultaneous appearance of the stamen and the stigma,

• the amount of pollen decreases; in extreme cases, the tassel loses unviable pollen,

• the stigma pierces out from among the husks wrongly; therefore, its pollen reception ability deteriorates,

• the stigma of certain mother lines does not even appear in critical cases and they will not become fertile.

In this period, one of the important aspects of irrigation is that the available water of the soil should be kept at 85-90%. Utmost care must be taken about keeping the upper 20-40 cm layer of the soil wet enough. Also, the microclimate of the population should be affected in a favourable way from the aspect of becoming fertile. In order to do this, irrigation should be carried out with a lower water dose but several times. Therefore, it is possible to increase the relative humidity at the level of the plant population and the adverse effect of the possible atmospheric drought can be reduced. Unfortunately, experience shows that the increase of humidity is limited even if the most modern irrigation devices are used. Even if 4-5% increase is achieved, if the period of flowering falls into extremely hot days, the air humidity can still remain below the necessary level.

3rd period: grain filling phase

After becoming fertile, it is important to cover the water need related to the incorporation of nutrients into the grain. This is a critical period in that the favourable thousand grain weight and the proper fraction ratio, i.e., good sowing seed quality depend on the availability of water in this phase.

Irrigation doses have to be planned in a way that the available water of the soil should be reduced to 40-60% by the period of ripening. Over-irrigation is harmful, because it slows down water loss, it creates favourable conditions for fusarium infection, it increases the frost damage in the case of long growing season lines and it contributes to weed infestation that makes harvesting more difficult.

In order to reduce the adverse impacts of atmospheric drought and to facilitate the undisturbed flowering and fertilisation, the most useful method of irrigation is sprinkler irrigation in sowing seed production. In the case of emergence irrigation, the initial dose should be 10-20 mm, then 30-40 mm in one application. The irrigation capacity has to be planned in a way to be able to perform irrigation again in 10 days, applying the above written doses.

3. Summary• Proper water management on irrigated corn can produce economic yields, conserve water supplies and

preserve or enhance water quality

• Use corn ET estimates and regular soil water measurements to determine irrigation timing and amount

• Consider the irrigation water supply and the system’s ability to deliver the water

• Work to maximize the efficiency of your irrigation system by performing regular maintenance

• Efficient irrigation management requires accurate records documenting the water applied and rainfall for each field


13. fejezet - 13. IRRIGATION MANAGEMENT OF MAIN CROPS: SOYBEAN1. Climate requirementsThe Hungarian varieties and the foreign cultivars that can be produced in Hungary need a heat sum between 2200-2500 °C. The difference between 2200-2500 °C is 20 days difference around the days of ripening. This is also coupled with the fact that varieties, which need higher heat sum also have higher yield potential. 30% of the needed heat sum is necessary until flowering. The largest heat need occurs from early flowering to when yellow start to turn yellow which is around 50-53% of the total heat need. Around 15-20% is needed from the appearance of the first yellow leaves to ripening. Taking these values into consideration, the available heat sum is always enough for varieties of different growing season except in mountainous areas.

As regards the heat need of soybean, it also has to be mentioned that the cold resistance of soybean is significantly better in its early development phase than that of bean, lupine, sunflower and even maize. Soybean also tolerates - 6-7 °C at young age if this condition does not last long. Only temperature lower than this can cause damage to the plant.

2. Crop water useThe water need of soybean is high, as it uses 750-800 l water for the production of 1 kg dry matter. As a matter of course, water consumption is also affected by environmental factors and nutrient supply has a determinant role from this aspect. The water need of soybean is different in each development phase; therefore, it is not the total yearly amount of precipitation, but its distribution over the year, which has an impact on yield.

Total water use by a fully irrigated soybean crop (evaporation plus transpiration) ranges from 533 to 640 mm per year. 65% of this water is used during the reproductive stages. As it is shown in Figure 38, water use at emergence will be under 2.5 mm per day. During the peak growing stage, daily water use can be 7.6 mm per day or more. Daily crop water use rates can reach 9 to 10 mm under hot dry conditions. Peak water use begins near full flowering and continues through pod development or pod-filling stage. As the crop reaches physiological maturity, water use drops below 2.5 mm per day.

13.1. ábra - Figure 38. General pattern of growth and water use for soybeans



CROPS: SOYBEAN(Source: modified from Thomas and Blaine, 2006)

Soybean has a high water need. Its undisturbed development is assured if the moisture content of the soil is above 70-75% of the field capacity. Soybean is the most sensitive to water supply and the humidity of air during flowering. In this period, it is especially important that the air humidity is between 70-75%. From the aspect of the level of water supply, the best areas are the ones where the amount of precipitation is above 160-180 mm in June, July and the first half of August. Soybean can be considered drought resistant in the period from emergence to flowering and also during ripening. Furthermore, there are significant differences between each cultivar in terms of drought resistance.

3. Soil requirementsSoybean is usually regarded as a plant that requires good quality soil. However, in accordance with the newest observations about its production, soybean does not have excessive demands towards soil if its culture conditions are adequate. As a matter of course, soybean is no different from the aspect that it can provide a high and steady yield only on soils with good nutrient supply, good water management and high fertility soils, which can warm up easily. Soils poorly supplied with nutrients, loose sandy soils, alkaline and gravelly soils are not suitable for soybean production. The pH of the soil does not affect production circumstances (except for extremities). Soybean can be produced on soils between pH 6 and 8 values.

4. Rooting characteristicsSoybean can be characterised a legume crop. Its nitrogen dimand can be supplied by nitrogen-fixing bacteria contained in nodules located in the plant roots (Figure 39). Although soybean roots can reach depths of 150 to 180 cm, the largest concentration of roots and the majority of soil water extraction occur in the top 90 cm of the soil profile. Therefore, irrigation water management should concentrate on the top 90 cm of soil and irrigations should replenish only the upper 75 to 90 cm of the root zone. This reduces deep drainage loss of irrigation water, and maintains some storage capacity for rainfall. Sandy soils do not hold a lot of water. More frequent, lighter irrigations are needed here than for crops grown on heavier soils.

Soybean produce highest yields on soils with good internal and surface drainage or a more common statement is ‘soybean do not like wet feet’.

13.2. ábra - Figure39. Soybean root nodules

5. Water stress and soybean yieldWater stress at some stages of plant development will have a greater effect on soybean yield than at others. Severe drought stress can stunt soybeans and have a lasting effect on yield; however, this seldom happens when timely planting occurs. If adequate soil moisture is available to germinate and establish a good stand, moderate



CROPS: SOYBEANwater stress in the early growing season has a mild effect on yield. Once a good stand is established and until beginning bloom, soybeans can tolerate short droughts with little or no effects on yield. The best program to follow is not to let soybeans stress at any time, even though some research shows no yield advantage to irrigation before bloom.

The most critical stage for water stress is the reproductive stage. Drought stress from beginning bloom through the pod-fill stage can greatly reduce yields (Figure 40). Inadequate moisture at this stage will result in a reduced number of fruiting sites, and poorly filled pods. As illustrated in Figure 41, research has shown that a 10 percent reduction in water use by soybeans during flowering results in an 8 percent reduction in eventual yield, while a 10 percent reduction in water use during pod filling leads to a 10 percent yield loss. When limiting irrigation water, it should be saved for flowering and pod set. Good soil moisture conditions need to exist from rainfall or irrigation to ensure adequate moisture from beginning bloom until the beans are touching in the pods.

13.3. ábra - Figure 40. Effect of wilting on soybean yields during reproductive growth stages

(Source: modified from Thomas and Blaine, 2006)

13.4. ábra - Figure 41. Effect of water stress on soybean yields at various growth stages



CROPS: SOYBEAN

(Source: modified from Kizer, 2009)

6. Soybean growth and irrigation managementThe most convenient way to time soybean irrigation is by using the crop stage- of-growth as an indicator. Stage-of-growth scheduling works well for crops like soybean that respond well to water supplied during the later growth stages. However, stage-of-growth scheduling also depends on the capability of the irrigation system to supply sufficient water to the crop. Precipitation during the growing season, stored soil moisture prior to the growing season, and irrigation system capacity combine to furnish water to the crop.

In this section, irrigation management based on different soybean growth stages is presented. The general facts of this method are listed here:

• Start your soybean irrigation before any visible signs of drought stress,

• Keep soil moisture above 50% available water-holding capacity in the active root zone,

• If inadequate off-season rainfall has left the soil profile depleted of moisture below the seedbed, early-season irrigation may be necessary,

• Waiting too late to begin, not repeating frequently enough, and ending too soon are the most common reasons for poor yield responses from irrigation,

• Failure to begin early enough can cause a yield loss that cannot be regained from later irrigations,

• Irrigate soybeans as frequently as necessary until pods have completely filled: number and frequency of irrigations will vary with the season, variety, soil, and irrigation system capability,

• Soybean that has been irrigated once becomes more sensitive to drought and air humidity,

• When limiting irrigation water, it should be saved for flowering and pod set.

7. Germination and SeedlingThe amount of irrigation water is affected by the precipitation shortage of the previous year. If good subsoil moisture is available throughout the root zone, the plant root system will develop normally and irrigation should not be needed for the first six weeks after planting. A lack of adequate moisture at or following planting can



CROPS: SOYBEANcause slow germination, poor stands, and slow early growth. If inadequate off-season rainfall has left the soil profile depleted of moisture below the seedbed and a dryer period after the sowing of soybean exist, early-season irrigation (30-40 mm) may be necessary to facilitate the initial development of a more balanced and strong population. Roots will not develop in dry soil. An initial profile of deep soil moisture helps ensure an adequate root system to carry the plant through heavy water use periods.

Late plantings and double-crop situations may require irrigation to ensure uniform stands, promote rapid early vegetative growth, and to activate preemergence herbicides.

8. Vegetative growthSoybeans normally will not show a yield increase from irrigation until just before bloom. If it is extremely dry during the vegetative growth stage, you may need irrigation to give the plants some height. Plants must have height at beginning bloom to allow for better harvest efficiency. Excessive water during the vegetative phase increases the potential for lodging and fungal diseases with no increase in yield.

9. Flower to full seedHigh temperatures during early reproductive growth (R1 to R3) can significantly reduce flower and pod retention, often negatively impacting yield. Proper irrigation prior to bloom can help to ensure canopy closure, and may potentially create a cooler microclimate during reproductive growth. With proper during initiation of reproductive growth irrigation, the crop may be able to withstand more heat and maintain adequate retention of pods and blooms.

The most important times for soybean to have adequate available water are during pod development (R3-R4) and seed fill (R5-R6). Irrigation may also be required during flowering on sandy soils or during very dry years on medium and fine-textured soils.

During an extremely dry season, delaying the beginning of irrigation until the pod-filling stage results in much lower yields, compared to beginning irrigation at prebloom or bloom stage. Waiting until pod fill to irrigate causes significant losses when compared to beginning irrigation at bloom.

10. Irrigation terminationAttention must be paid to not to irrigate in the second half of August, because ripening will be uneven and the soil which is irrigated too late also blocks the movement of harvesters.

Determine if 50% or more of the pods have seeds that are touching within the pod. If there is good soil moisture at this point, then irrigation can be ended. If the soil is becoming dry, an additional irrigation is needed to assure maximum seed weight. A final irrigation at this stage should be as quick a flush as possible if flood, border or furrow irrigating. About 25 mm should be applied with a pivot at this time. In 5 to 7 days soil moisture and crop development should be checked again to determine if an additional irrigation is needed.

11. Irrigation recommendationsRecommendations for coarse-textured soils

Water management for coarse textured soils is more difficult than for medium-textured soils since there is less room for error in timing irrigations. Soils in this classification include fine sands, loamy sands and fine sandy loams. Generally, these soils have a low (less than 125 mm/m) available water-holding capacity, and some have root-restricting layers at shallow depths. The combination of low available water-holding capacity and shallow rooting results in a small soil water reservoir. The available water-holding capacity in a 90 cm active root zone will be 60 to 115 mm. This low available water-holding capacity, coupled with the fact that sprinkler systems will likely be the irrigation used, means light, (12 to 25 mm), frequent water applications are necessary to recharge the limited soil water reservoir.

The general recommendation for water management on coarse-textured soil is to allow no more than 50 percent depletion of the available soil water in the top 60 cm during flowering (R1-R2) and no more than 50 percent depletion in the top 90 cm during pod elongation (R3-R4) and seed fill (R5-R6). Soil water levels can be



CROPS: SOYBEANdetermined by combining the crop appearance method with soil water-balance calculations using reliable evapotranspiration estimates.

Recommendations for deep fine-textured soils

These soils (silt loams, silty clay loams, silty clay) generally have an available water capacity of more than 125 mm per m. The available soil water at field capacity is between 115 and 150 mm in the top 90 cm. Applying irrigation water when the available soil water is depleted to 50 percent in the top 90 cm of the root zone after the full flower stage (R2) will generally result in maximum yields. The same methods mentioned for the sandy soils can be used to estimate soil water in these soils.

An alternative scheduling approach on deep- and fine-textured soils is stage-of-growth scheduling. This method works if the soil water reservoir is at or near field capacity to 150 cm at planting time. This usually occurs if the soils were irrigated during the previous season and there was sufficient off-season precipitation to refill the profile.

For soybeans, between 255 and 280 mm of water are required from full flower (R2) to beginning maturity (R7). Therefore, effective irrigation plus rainfall should equal about 75 mm during full flower (R2), 75 mm during pod development (R3-R4) and 115 mm during seed fill (R5-R6). With adequate rainfall, optimum yields will be obtained with two, 75 mm net or effective furrow irrigations (typically at full flower or pod development and beginning seed fill). With systems such as center pivots applying smaller amounts of water per irrigation, it will be necessary to make two to four revolutions to apply the desired 75 mm during a particular growth stage. In dry years, an additional 75 to 125 mm of effective irrigation may be required.

If irrigation is started or unusually significant rainfall occurs during the beginning flower stage (R1), it is especially important adequate soil water (50 percent available soil water or greater) be maintained during the remainder of the growing season. If you are limited in the amount of irrigation water you can apply during the season, you will get the maximum benefit of this water if it is applied during the pod development (R3-R4) and seed fill (R5-R6) growth stages. However, when the rainfall is below normal during the vegetative and flower stages, a yield reduction may occur.

With furrow irrigation systems, it is generally not advisable to wait until pod development (R4) before applying the first irrigation, as this will probably cause extremely dry furrow conditions, making it difficult to get water through the field. An earlier irrigation date, perhaps beginning during the full flower stage, is advised. Individual effective irrigation applications should not exceed 75 mm.

Because precipitation decreases from west to east across Hungary, a full soil water reservoir may not always exist at planting time in the Great Plain. In this region, conventionally the following irrigation water doses proved to be necessary in the average of several years during dryer crop years: 30 mm in May, 40 mm in June and 90 mm in July. Depending on the given weather circumstances, 40-60 mm doses need to be applied on 2-3 occasions in dryer crop years.

Irrigation recommendations to maintain profitability

Irrigation recommendations for soybean in the past have been based onproperly utilizing irrigation to produce a 4.5 to 5.0 tons per hectare soybean crop while maintaining profitability at much lower market prices. To meet those criteria, the following recommendations were created and have been used for many years.

The following water balance method is suggested for 4.5 to 5.0 tons per hectare soybean yields (Table 24):

13.1. táblázat - Table 24. Irrigation recommendations for soybean to maintain profitability (Source: Whitaker, 2012)

Growth Stage Trigger Amount (mm)

Stand Establishment Irrigate prior to planting 25-38

Prior to 1st Bloom (VE – R1) Wilting by late afternoon 25-38



CROPS: SOYBEAN

1st Bloom – Beginning Pod Elongation (R1 – R4) Wilting by mid-day 25-38

Beginning Seed – Full Seed (R5 – R6) Keep from wilting 25-38

Full Seed – Maturity (R6 – R7) Wilting by late afternoon 25

Total amount of irrigation water 125-175

12. Irrigation schedulingThe timing of irrigation is commonly referred to as irrigation scheduling. Correct timing is critical to maximizing yield. Having the ability to irrigate is important, but it is also essential that a grower have a commitment to apply irrigation in a timely manner. Too often growers irrigate by the appearance of the crop. Considering plant conditions to time irrigations is less desirable since they indicate the plant is already stressed and the optimum irrigation opportunity is past. Visual stress, especially during bloom and pod set, results in yield loss. Also, once irrigation is started, the time required to finish a field will result in part of the crop suffering even greater stress.

If the soil moisture can be determined, then irrigation timing decisions can be improved. You can use different instruments to monitor soil moisture. Tensiometers and eletrical resistance sensors use soil matrix potential to indicate the available soil moisture, capacitance sensors (TDR and FDR) measure the volumetric moisture content of the soil.

One of the more commonly used tools in soybean is called a tensiometer, which is a sealed, water-filled tube with a porous, ceramic tip and a vacuum gauge on the upper end. When properly installed and maintained in the soil, a tensiometer measures the soil moisture tension, which is an indicator of the availability of water to the plant. The greater the tension, the more tightly the water is held by the soil and the lower the availability for plant use.

The tensiometer is installed in the seedbed at a depth where the majority of the roots are located. A 30 cm depth is commonly used for surface irrigation, except where a hardpan exists, and there it is placed just above this layer. Shallower settings at about 20 cm deep are recommended for center pivots. Place tensiometers at representative sites within the field on the predominant soil type. Placements at the upper and lower ends of the field and in the first and last irrigation sets are most useful. The location of the instruments allows measurement of the wet to dry gradient in the field from where the irrigation began to where it finished. This gives you an idea as to how fast the field is drying out and when to start irrigation again.

Starting irrigation at a vacuum gauge reading of 50-60 centibars on silt loam and clay soils, and 40-50 centibars on sandier soils, is recommended. Tensiometers are fairly reliable and effective when checked and maintained properly. However, the time and effort required usually results in most producers not being able to use them very effectively.

A more precise scheduling method is offered by combining soil moisture monitoring with water balancing and automated weather stations, ET-based irrigation computer software programs, crop simulation models.

13. Evaluation methods of irrigation for soybeanFlood, border, furrow, traveling gun sprinklers, center-pivot sprinklers, and linear-move sprinklers and subsurface drip irrigation are all systems that can do a satisfactory job if properly designed and managed. They vary in efficiency and cost. Base your selection on these factors, your field’s topography, the soil’s physical factors, labor costs, and on your management capabilities.

14. Surface irrigationsFlood irrigation method requires levees that take away land area for production, take time to survey and construct, and take time to get out after the irrigation. Generally, levees are surveyed on elevations of no more than 12 cm. Flood irrigation is very risky for a germination irrigation or irrigation of small beans. Getting levees



CROPS: SOYBEANto hold water can be another problem with a flood system. Getting water on and off rapidly (within 48 hours) is critical for good soybean growth and development. Flood irrigation is typically 50 to 60 percent efficient.

Border system is a cross between flood and furrow irrigation and best fits straight levee rice fields or fields with no side slope. It is a flush system that moves water down the slope in a shallow flush between two small levees or dikes (borders). The border spacing is based on the well’s flow rate and the length of the field. Most border systems are designed to move water through a bay in 12 to 24 hours maximum. The cracking clays make this a uniform system for soybeans and simple to operate once it is set up. The efficiency is 60 to 80 percent in most cases and can be used on small beans. It is similar to furrow except it is ideal for flat-planted beans and works best where there are no side slopes involved. Border irrigation is not recommended for germinating soybeans but could help with germination in spotty stands, if it is not too hot.

Furrow system requires grading the land to a slope of 5 to 50 cm per 100 m of row. The best row grades are 0.15 to 0.3 percent. Gated or roll-out pipe is most often used. Considerable labor is required for handling pipe; consequently, more and more farmers are buying enough pipe to put in place for an entire season or using roll-out tubing. Problems are often associated with uneven distribution of water down the row. It helps to keep irrigation runs to 400 m or less and to water clay soils before they crack too badly. Large stream sizes per row will get water through the field quicker and more efficiently than will a small stream size that may take up to 3 days to get down a row. Furrow irrigation efficiency can range from 50 to 70 percent.

It should be noted that surface irrigation methods are not widely used for soybean in Hungary. Sprinkler methods like linear-move and travelling guns are the preferred irrigation systems in soybean growing areas.

15. Sprinkler irrigationsCenter pivot and linear-move sprinkler systems can supply smaller amounts of water more frequently than can the flood or furrow methods. Most pivots and linear-move systems are nozzled with capacities, which just meet normal demand for soybeans. They require little labor but high capital investments. Efficiency of water applied is about 80 to 90 percent, depending on weather conditions.

The traveling gun sprinkler system has an advantage in irrigating small, irregular-shaped fields. Size this system at nothing less than 5 gpm per acre to be irrigated. It typically has a higher cost per acre than does a center pivot or a linear-move and requires more labor and energy. The application efficiency is about 70 to 80 percent for the traveling gun.

16. Subsurface drip irrigationSubsurface drip irrigation is another irrigation method that has been gaining popularity in areas with limited water. The method has been used only on limited bases in the commercial production of soybeans. Polyethylene drip tubing is plowed into the field, between alternate soybean rows prior to planting, generally at a depth of 30 to 38 cm. The tubing must be buried deep enough to ensure sufficient capillary rise of the irrigation water to allow proper wetting throughout the root zone. Application efficiency of subsurface drop irrigation is 95 percent in most cases. The system is very well adapted to automated operation. Many of the disease problems associated with high humidity in the crop canopy from irrigation are reduced or eliminated. Initial system costs are high, and the system must be properly maintained by filtering and treating the water to allow reuse of the tubing for several years.

17. Summary• Irrigation is not a cure-all. Maximum yield and profit will be achieved only when irrigation is coupled with

other production practices that establish profitable yield potentials,

• Meet all sound agronomic production practices before considering irrigation,

• Stage-of-growth irrigation scheduling should be limited to deep medium- to fine-textured soils,

• Select a system to fit soil, labor, capital, and management needs,

• Provide good surface drainage for all irrigation systems,



CROPS: SOYBEAN• Begin watering soon enough to avoid stress,

• Avoid overwatering clays and silt loams,

• Use flood, border, or furrow irrigation on clay soils before they are heavily cracked,

• Apply at least 25 mm of water per application with sprinklers during peak water use, and repeat based on a 6.5-mm-per-day gross use,

• Repeat furrow and flood irrigations regularly (every 8 to 10 days) during peak water use, unless adequate rainfall occurs,

• Continue irrigating until beans are touching in the pods.


14. fejezet - 14. IRRIGATION MANAGEMENT OF MAIN CROPS: RICE1. Rice environmentsWorldwide, there are about 150 million hectares of rice land, which provide around 550-600 million tons of rough rice annually. Rice is unique among the major food crops in its ability to grow in a wide range of hydrological situations, soil types, and climates. Rice is the only cereal that can grow in wetland conditions.

Depending on the hydrology of where rice is grown, the rice environment can be classified into irrigated lowland rice (79 million ha), rainfed lowland rice (54 million ha), flood-prone rice (11 million ha), and upland rice (14 million ha). Lowland rice is also called “paddy rice”. Lowland rice fields have saturated (anaerobic) soil conditions with ponded water for at least 20% of the crop’s duration. Irrigated rice is mostly grown with supplementary irrigation in the wet season, and is entirely reliant on irrigation in the dry season in Asia. In irrigated lowlands, the availability of irrigation assures that ponded water is maintained for at least 80% of the crop’s duration. In rainfed lowlands, rainfall is the only source of water to the field and no certain duration of ponded water can be assured (depending on vagaries of rainfall). In flood-prone environments, the fields suffer periodically from excess water and uncontrolled, deep flooding (more than 25 cm for 10 days or more). Deepwater rice and floating rice are found in these environments. Upland rice fields have well-drained, nonsaturated (aerobic) soil conditions without ponded water for more than 80% of the crop’s duration.

2. Climate requirementsHeat need. The heat threshold value of rice assimilation is 10 °C. Of climate elements, mainly temperature fluctuates extremely in the spring. The duration of daily mean temperature above 10 °C (from spring to autumn) exceeds 180 days in the region. The effective heat sum above 10 °C is nearly 1400 °C in a 30-year average. The extreme values were between 1200-1500 °C. The lower values show heat shortage and while higher values are more favourable for rice. The critical periods of the heat demand of rice are germination, tillering, and the phenophase of flowering. The optimum mean temperature values what provide quick development are 12-14 °C during germination, 16-18 °C during tillering and 20-22 °C or higher during the development of flowering. In the case of large heat fluctuation, the development of rice is held back, the sterility of the cluster increases; therefore, yield decreases even in the case of the above written mean temperature values.

Sunshine duration. The sunshine duration need of rice is different depending on the given development phase. In the vegetative stage (early May-July), sunshine duration has a less pronounced impact on yield components. However, this effect increases in the reproductive phase (July-August). In this period, sunshine duration is in positive correlation with grain yield.

Precipitation. Precipitation mainly has an indirect role as it affects soil preparation in the spring, as well as sowing, crop protection activities and harvesting. Also, rainy crop years are cold and there is little sunshine, which inhibits the development and ripening of rice.

3. Soil requirementsRice belongs to the group of crops that are not too sensitive to various soil types. However, this does not mean that rice can be produced on any soil, as it is especially sensitive to certain soil characteristics. It is a basic requirement towards the soil of the rice to have a 20-25 cm thick impermeable layer under the cultivated layer in order to save irrigation water. The total salt content of the soil should not exceed 0.4-0.6%, while the soda content shall not reach 0.1%. Rice prefers slightly acidic soils, pH 5-6 is considered to be optimum. The solognac, solognac meadow and meadow soils in Hungary meet these requirements. Rice can also be produced on solognac soil for a short period of time, but it is not economical, since the yield is low, the fertile layer of these soils is shallow, the groundwater level is close to the surface, the soil plasticity is high and their water and air management is unfavourable. Lately, rice production has been extended to meadow soils of relatively higher



CROPS: RICEproductivity.

Traditional rice production is not substantiated on soils, which have better nutrient, water, air and heat balance, since they can have better use in field crop production.

4. Rice rooting characteristicsA typical vertical cross-section through a puddled rice field shows a layer of 0-10 cm of ponded water, a puddled, muddy topsoil of 10-20 cm, a plow pan that is formed by decades or centuries of puddling, and an undisturbed subsoil. Rice roots are usually contained within the puddled layer and they generally do notpenetrate the compacted layer. The root zone is therefore quite shallow. The plow pan reduces the hydraulic conductivity and percolation rate of rice fields dramatically (Figure 42).

14.1. ábra - Figure 42. Water balance and rooting zone of lowland rice

(Source: Bouman et al., 2007)

5. Water requirements5.1. Global rice water useThere are no data available on the amount of irrigation water used by all the rice fields in the world. However, estimates can be made based on total worldwide water withdrawals for irrigation, the relative area of irrigated rice land (compared with other crops), and the relative water use of rice fields.

Total worldwide withdrawals of fresh water are estimated at 3,600 km3 annually, of which 2,500 km3 is used to irrigate crops. The rest is used in industry and for domestic purposes. Assuming a reuse fraction of 25%, it can be estimated that irrigated rice receives some 34-43% of the total world’s irrigation water, or 24-30% of the total world’s freshwater withdrawals. Approximately 56% of the world’s 271 million ha of irrigated area of all crops is in Asia, where rice accounts for 40-46% of the net irrigated area of all crops. Figure 30 gives irrigated areas and volumes of irrigation water used in agriculture and in rice.

5.2. Rice water use and irrigation need at field levelBecause of its flooded nature, the rice field has a water balance that is different from that of dryland crops such as wheat or maize. The water balance of a rice field consists of the inflows by irrigation, rainfall, and capillary rise, and the outflows by transpiration, evaporation, overbund flow (surface runoff), seepage, and percolation (Figure 43). Of all water outflows, runoff, evaporation, seepage, and percolation are non-productive water flows



CROPS: RICEand are considered losses from the field. Only transpiration is a productive water flow as it contributes to crop growth and development.

14.2. ábra - Figure 43. Irrigated areas (A) and volumes of irrigation water used (B) in the world, in Asia, and in rice production

(Source: Bouman et al., 2007)

Capillary rise is the upward movement of water from the groundwater table. In nonflooded (aerobic) soil, this capillary rise may move into the root zone and provide a crop with extra water. However, in flooded rice fields, there is a continuous downward flow of water from the puddled layer to below the plow pan (called “percolation”; see below) that basically prevents capillary rise into the root zone. Therefore, capillary rise is usually neglected in the water balance of rice fields.

When rainfall raises the level of ponded water above the height of bunds, excess rain leaves the rice field as surface runoff or overbund flow. This surface runoff can flow into a neighbouring field, but, in a sequence of fields, neighbouring fields will pass on the runoff until it is lost in a drain, creek, or ditch.

Evaporation leaves the rice field directly from the ponded water layer. Transpiration by rice plants withdraws water from the puddled layer. Typical evapotranspiration rates of rice fields are 4-5 mm per day in the wet season and 6-7 mm per day in the dry season, but can be as high as 10-11 mm per day in subtropical regions.

Seepage is the subsurface flow of water underneath the bunds of a rice field. With well-maintained bunds, seepage is generally small. Considerable seepage can occur from top-end fields and from bottom-end fields that border drains, ditches, or creeks. During the crop growth period, about 30-40% of evapotranspiration is evaporation.

Percolation is the vertical flow of water to below the root zone. The percolation rate of rice fields is affected by a variety of soil factors: structure, texture, bulk density, mineralogy, organic matter content, and salt type and concentration. Soil structure is changed by the physical action of puddling. In a heavy-textured, montmorillonitic clay, sodium cations and a high bulk density are favorable for effective puddling to reduce percolation rates. In practice, seepage and percolation flows are not easily separated because of transition flows that cannot be classified as either percolation or seepage. Typical combined values for seepage and percolation vary from 1-5 mm per day in heavy clay soils to 25-30 mm per day in sandy and sandy loam soils. Some examples of seepage and percolation rates measured at different sites are presented in Table 25. Water losses by seepage and percolation account for about 25-50% of all water inputs in heavy soils with shallow groundwater tables of 20-50 cm depth, and 50-85% in coarse-textured soils with deep groundwater tables of 1.5 m depth or more.

Evaporation from ponded water surfaces is higher than from soil surfaces (as in dryland crops). Therefore, it is the relatively large water flows by seepage, percolation, and evaporation that make lowland rice fields heavy “water users”. Total seasonal water input to rice fields (rainfall plus irrigation) can be up to 2-3 times more than for other cereals such as wheat or maize. It varies from as little as 400 mm in heavy clay soils with shallow groundwater tables (that directly supply water for crop transpiration) to more than 2,000 mm in coarse-textured (sandy or loamy) soils with deep groundwater tables. Around 1,300-1,500 mm is a typical value for irrigated



CROPS: RICErice in Asia. Table 25 lists some values for water inputs and daily seepage and percolation rates for lowland rice fields in China and the Philippines.

14.3. ábra - Table 25. Total seasonal water input and daily seepage and percolation rates from lowland rice fields with continuously ponded water conditions >(Source: modified from Bouman et al., 2007)

Rice is a hydrophyte crop; therefore, irrigation is a prerequirement of rice production under Hungarian circumstances. The water demand of rise is relatively low, despite the fact that continuous water coverage is needed during the whole growing season or most of it. The ET value of rice is 500-700 mm.

The irrigation water need of rice is 10-12 thousand m3 per hectare under Hungarian conditions. This value can be lower in well-established rice plantations and more if the plantation is improperly arranged. The components of irrigation water use show properly that hardly more than 40% of the applied irrigation water is evaporation. Seepage and condensing loss is nearly 50%. Therefore, irrigation water can be economically used by properly establishing and operating the rice plantation. The water coverage is affected by the crop needs and the prevailing ecological needs. The most favourable depth of flood water depends on various factors, such as the development phase of rice, its variety, the weather and the current crop health circumstances. Usually, more shallow water (3-5 cm) is favourable in the first half of the growing season, while it is preferred to have a deeper (5-8 cm) layer in the second half.

Moist soil is enough for germination and the emergence of rice. Flooding is not necessary in the early development phases of rice, except in the case of broadcasting and sowing into floodwater. In the case of broadcasting, flooding has to be performed directly after sowing, while in the case of sowing rice into water, the field has to be flooded directly before sowing. In this case, the thickness of the water layer should not exceed 3-5 cm. In the case of sowing into the soil, permanent flooding should end at the 2-3 leaf stage of rice. The water layer has to be 3-5 cm thick. As the development of rice progresses, the thickness of water coverage has to be gradually increased. The water coverage should not exceed 7-8 cm in the phenophase of tillering, because the tillering node of rice needs light.

In the period of reproductive development in the second half of the growing season of rice, 10 cm water layer has to be provided due to the significant increase of evaporation and the heat balancing effect of water. The day-nigh fluctuation of the root zone temperature is low at such depth of water. However, a 2-3 day fall in temperature also cools down the flood water; therefore, water coverage has to be reduced in such cases (by drainage) in order to facilitate quicker warm-up of the water and root zone if the temperature rises again.

As the ripening of rice approaches, the water level of rice fields has to be gradually decreased. However, ripening has to start before the final drainage. Therefore, after the flooding of rice fields, rice needs the continuous maintenance of water cover until ripening. In the meantime, water is drained only if needed (crop protection activities). However, water level is professionally regulated in accordance with the above written rules.

Rice and the soil of rice fields need irrigation water that does not contain harmful substances. In order to not to cause any damage, only irrigation water containing less than 500 mg per liter salt of which the Na content is less than 35-45% can be used. The rivers in the rice production regions of Hungary (Tisza, Körös) meet this quality requirement. In other places, irrigation from the drainage water main ducts causes problems, as this water exceeds the limit value of total salt content and Na content.



CROPS: RICE

6. Field preparation6.1. Land gradingYearly preplant field leveling or smoothing is essential for seedbed preparation, surface drainage and maintaining optimum flood depths. A landplane or float should be used to remove reverse grades, fill „potholes” and smooth out old levees, rows or ruts in a field. Rice can germinate under either soil or water, but not both. Therefore, maintaining a field surface that provides good drainage is important for stand establishment; controlling weeds, diseases and insects; maintaining desired flood depths; and providing a dry field for harvesting.

Precision land grading is desirable, but not absolutely necessary. Recent innovations using laser systems have made precision levelled or graded fields physically and economically feasible. Precision grading of fields to a slope of between 0.05 and 0.1% change in elevation between levees is generally recommended in rice production for the following reasons:

• Permits uniform flood depth,

• May eliminate a large number of levees,

• Facilitates rapid irrigation and drainage,

• Can lead to the use of straight, parallel levees that will increase machine efficiency

• Eliminates knolls and potholes that may cause delay of flood or less than optimum weed control,

• Reduces the total amount of water necessary for irrigation.

6.2. Establishing LeveesAn accurate levee survey is important to assure proper control of water. All surveying instruments should be properly adjusted and checked for accuracy. Be careful not to exceed the operating range or distance of the equipment. A levee elevation difference of no more than 0.2% is generally recommended. This difference is increased on steeper fields when narrow distances between levees present a problem for combine operation. Premarking levees on clay soils and establishing levees as soon as conditions allow can reduce water loss from levee seepage. Levee gates should be installed early in case flushing is necessary and also to provide outlets to avoid levee washouts in case of a heavy rain. One gate per levee is usually adequate.

7. Sowing methods7.1. Water plantingUsually implemented for any or all of the following reasons: red rice control, wet planting season, planting efficiency and earlier crop maturity. Sowing into water is possible both in flooded or dry seedbed. With sowing into a flooded field, seedbed is prepared following flood establishment (mudding in). This wet land preparation consists of soaking, plowing, and puddling (i.e., harrowing or rotavating under shallow submerged conditions). Puddling is done to control weeds, to reduce soil permeability, and to ease transplanting. Puddling leads to a complete or partial destruction of soil aggregates and macropore volume, and to a large increase in micropores. In this system, a flood is established with the rice seed being seeded directly into the floodwater. Sowing of pregerminated seed is performed by airplane. The floodwater is then released and rice seedlings are allowed to peg into the soil.

Because red rice and commercial rice are so closely related genetically, herbicides that control red rice will generally kill commercial rice. Water management alone can often effectively suppress red rice and reduce competition. Presence of red rice mandates that rice be produced in a water-seeded system. Uniform, level seedbeds are critical for success.

Dry seedbed. You can prepare a dry seedbed in the springbefore flood establishment, to reduce the possibility of seed drift, a grooving implement can be used. The result is a seedbed with grooves 2.5 to 5 cm deep on 18 to 25



CROPS: RICEcm centers. In some cases, a field cultivator can do an acceptable job. The shallow grooves provide a depression for the seed to fall into and give some protection from wave action. If water planting with dry seedbed is used, the rice field has to be flooded 1-2 days before sowing. The flood water has to be maintained at 3-5 cm. Pregerminated seed can be sown by airplane.

7.2. Dry plantingSowing seed into the soil (drilling). During sowing into the soil, cereal row spacing is used with a sowing depth of 3-4 cm. In order to properly perform sowing, well-prepared, tiny crumbed seedbed is needed. If this type of seedbed is not provided, this sowing method is not recommended. The preferred cereal sowing machine should perform sowing at a steady depth, keeping an equal distance between the grains. Good quality sowing is one of the basic requirements of steady, well-adjusted crop population. If the soil is properly moist at planting, there is no need for irrigation, rice will emergence even with the natural moisture of the soil. If there is not enough moisture in the soil for emergence, post-plant irrigation („running flooding”) should be used. Running flooding can only be performed on rice fields of good technical conditions. It is an important requirement of this job that no water ponding can be left after soaking the soil properly, as the remaining water patches could cause severe germ perishing. In order to facilitate the development of rice and to stop the cracking of soil, running flooding can be repeated if necessary.

With no-till, sowing is performed into previous crop residue, native vegetation without any soil disturbance. Usually requires application of preplant burndown herbicide to kill volunteer vegetation before planting. No disking of residue, water leveling or any other mechanical soil-disturbing activity is done.

The rice field should be permanently flooded at the 2-3 leaf stage of the crop. The water layer should not cover the upper third part of rice. It is the advantage of sowing rice into the soil that it sprouts a stronger root system after emergence; therefore, the wave action will not sweep it away from its place. It is a further advantage that the floodwater does not have to be released before chemical post-emergent weed control as it is done prior to flooding. However, its real advantage is shown if a uniform and good quality crop population is developed without post-plant irrigation.

Sowing seed onto the surface of dry seedbed (broadcasting). Broadcasting calls for a smooth surface that is developed with smooth or ringed roller. Broadcasting has to be carried out with a sowing machine with elevated furrow splitters and seeds should be pressed with smooth roller to the soil. After sowing, the rice field has to be flooded in order to reduce the damage done by birds and to provide water to the seeds, thereby facilitating germination.

The advantage of this sowing method is that even a slightly delayed sowing can be successful. Early flooding kills some weeds or at least delays weed proliferation. It is the disadvantage of early flooding that the roots of the rice crop will be weak for a long time. As a result, many crops could be swept away by the wave action of water that is caused by wind. The field has to be drained even for the post-emergent weed control.

7.3. TransplantationIn the original home of rice, transplantation of seedlings is the general form of rice production. Rice seedlings are grown in the early sown, intensively cultivated and fertilised seedling garden. The amount of seeds sown into 1 ha seedling garden is calculated so that the seedlings will be enough for 10-12 ha. Planting is performed 40-50 days after sowing, when plant height is about 20 cm. Traditionally, planting is done manually, while planting machines are also used. Machines are usually used in areas moderately flooded with water. The leaf tips of seedlings and in some countries their roots are cut back. In accordance with the production circumstances and the population density depending on the given variety, seedling nodes consisting of 5-10 seedlings are planted.

In Hungary, producers first tried to introduce the planting production method in 1940, and later in the late 70’s. During the latter attempt, they used the mechanised seedling cultivation and planting technology developed by the Japanese. The farmers considered the advantage of this method to be the fact that the seedling cultivation was performed under regulated circumstances, under foil, in the first phase of the development of rice, which is a significant part of its growth from the Hungarian aspect. Flowering can be brought forward, the crop population will become more even, while the process of becoming fertile and grain filling will also improve.

The expected advantage of the planting production technology was not obtained in Hungary after several years of trying. However, this technology can still be used in variety management,which calls for smaller areas, as



CROPS: RICEwell as in the production of super elite and elite sowing seeds because the propagation ratio is significantly higher than in the case of direct sowing.

8. Evaluation of rice irrigation systems8.1. Sprinkler Irrigated RiceSprinkler irrigation should be used on an experimental basis only, and the following recommendations should be considered:

• Don’t attempt on silt loam soils that tend to crust or seal,

• Use residual herbicide program,

• Be certain sufficient water is available during reproductive growth (after joint movement),

• Be prepared to use phenoxy herbicides at midseason,

• Plant rice varieties with blast resistance.

Research and experience show that the best potential is either on clay or sandy loam soils that are relatively free of johnsongrass. Many silt loam soils tend to crust which causes excessive runoff and inadequate infiltration in the soil. This can lead to drought stress or excessive irrigation, which generally results in decreased yields and increased pumping costs. Rutting and sticking of the center pivot is also a potential problem. There is also a possibility that certain disease problems could be increased when the foliage is wetted at the frequency associated with sprinkler irrigation.

8.2. Multiple Inlet IrrigationThe basic concept of multiple inlets is to proportion the irrigation water evenly over the whole field at one time. The proportioning is accomplished by placing irrigation tubing across each paddy (area between levees) and releasing water into each paddy at the same time through holes or gates in the tubing. Tubing can be placed along the side of the field or through the field depending on the location of the irrigation source. This can be done on fields with straight levees and also on fields that have crooked levees (see Figure 44).

14.4. ábra - Figure 44. Multiple Inlet Rice Irrigation. Contour of straight leeves

(Source: Slaton (ed), 2006)

The potential for improved water management provided by multiple inlets and a few potential disadvantages or problems that can occur with multiple inlets are demonstrated in Table 26:

14.1. táblázat - Table 26. Advantages and disadvantages with Multiple Inlet Rice Irrigation (Source: own editing on the basis of Slaton (ed), 2006)



CROPS: RICE

Advantages Disadvantages/Risks

Reduces pumping time during season Cost of riser bonnets (universal hydrants) and irrigation tubing

Reduces pumping cost Initial installation of irrigation tubing and initial adjustment of the inlets (holes or gates)

Reduces amount of water pumped Floating, moving and twisting of irrigation tubing early in the season

Reduces runoff from field Working around or over irrigation tubing with field equipment (i.e., spraying levees)

Reduces irrigation labor Animal damage to tubing

Reduction in cold water effect Removal and disposal of tubing

Avoids risk of washing out levees from over-pumping top levees

Reduces problems associated with scum and algae buildup in levee spills (gates)

Can flood field quicker – increased fertilizer and herbicide efficiency

9. Methods for managing rice water scarcityIn this paragraph, technology options are presented to help farmers to cope with water scarcity at the field level in the tropical and subtropical rice growing areas. The way to deal with reduced (irrigation or rain) water inflows to rice fields is to reduce the non-productive outflows by seepage, percolation, or evaporation, while maintaining transpiration flows (as these contribute to crop growth). This can be done at land preparation, at crop establishment, and during the actual crop growth period.

9.1. Saturated soil cultureIn saturated soil culture (SSC), the soil is kept as close to saturation as possible, thereby reducing the hydraulic head of the ponded water, which decreases the seepage and percolation flows. SSC in practice means that a shallow irrigation is given to obtain about 1 cm of ponded water depth a day or so after the disappearance of ponded water. Research results reported water savings of 5-50% with yield reduction of 10-34% under SSC compared to flooded rice.

Practical implementation. Although conceptually sound, SSC will be difficult to implement practically since it requires frequent (daily or once every two days) applications of small amounts of irrigation water to just keep a standing water depth of 1 cm on flat land, or to keep furrows filled just to the top in raised beds.

9.2. System of Rice IntensificationThe System of Rice Intensification (SRI), an integrated crop management technology was developed by the Jesuit priest Father Henri de Laulanie in Madagascar. SRI is characterized by the following practices:

• Transplanting 8- to 12-day-old single seedlings very carefully (root tip down),

• Spacing the plants widely apart in a square pattern (25 × 25 cm or wider),



CROPS: RICE• Controlling weeds by weeding with a rotating hoe, which aerates the soil,

• Applying compost to increase the soil’s organic matter content (optional),

• No continuous flooding during the crop growth period, applying small amounts of water regularly or alternating wet and dry (AWD) field conditions to maintain a mix of aerobic and anaerobic soil conditions,

• After flowering, a thin layer of water should be kept on the field, although some farmers find alternate wetting and drying of fields throughout the crop cycle to be feasible and even beneficial.

9.3. Alternate wetting and dryingAlternate Wetting and Drying (AWD) is the water management practice of the System of Rice Intensification (SRI). AWD is a mature technology that has been widely adopted in China. It is also a recommended practice in northwest India, and is being tested by farmers in the Philippines.

In AWD, irrigation water is applied to obtain flooded conditions after a certain number of days have passed after the disappearance of ponded water. The number of days of non-flooded soil in AWD before irrigation is applied can vary from 1 day to more than 10 days.

The following potential benefits of AWD have been suggested: improved rooting system, reduced lodging (because of a better root system), periodic soil aeration, and better control of some diseases such as golden snail. On the other hand, rats find it easier to attack the crop during dry soil periods. For the purpose of water savings, we recommend the combination of AWD with well-researched and site-specific best management practices (integrated crop management).

Practical implementation. A practical way to implement AWD is to monitor the water depth in the field using the “field water tube” (Figure 45). After an irrigation application, the field water depth will gradually decrease over time. When the water level (as measured in the tube) is 15 cm below the surface of the soil, it is time to irrigate and flood the soil with a depth of around 5 cm. Around flowering, from 1 week before to 1 week after the peak of flowering, ponded water should be kept at 5cm depth to avoid any water stress that would result in potentially severe yield loss.

The threshold of 15 cm is called “Safe AWD” as this will not cause any yield decline since the roots of the rice plants will still be able to take up water from the saturated soil and the perched water in the root zone. The field water tube helps farmers see this “hidden” source of water. In Safe AWD, water savings may be relatively small, on the order of 15%, but there is no yield penalty. After creating confidence that Safe AWD does not reduce yield, farmers may experiment by lowering the threshold level for irrigation to 20 cm, 25 cm, 30 cm, or even deeper. Some yield penalty may be acceptable when the price of water is high or when water is very scarce. Remember that, in many irrigated areas, the groundwater is very shallow and may reach into the field water tube!

In Safe AWD, the following rules should be observed. AWD irrigation can be used from a few days after transplanting (or a 10-cm-tall crop after direct seeding) till first heading. In the period of first heading to 1 week after flowering, keep the field flooded with 5-cm depth. After that, during grain filling and ripening, apply AWD again.

14.5. ábra - Figure 45. Field water tube for monitoring the depth of standing water in AWD



CROPS: RICE

(Source: Slaton (ed), 2006)

9.4. Aerobic riceA fundamentally different approach to reduce water outflows from rice fields is to grow the crop like an upland crop, such as wheat or maize. Unlike lowland rice, upland crops are grown in non-puddled, non-saturated (i.e., “aerobic”) soil without ponded water. When rainfall is insufficient, irrigation is applied to bring the soil water content in the root zone up to field capacity after it has reached a certain lower threshold level, such as halfway between field capacity and wilting point. The amount of irrigation water should match evaporation from the soil and transpiration by the crop (plus any application inefficiency losses). Besides seepage and percolation losses declining, evaporation decreases since there is no ponded water layer, and the large amount of water used for wet land preparation is eliminated altogether.

Successful examples of the adoption of aerobic rice by farmers in the tropics (rainfed uplands in Philippines) showed total water input was 1,240−1,880 mm in flooded fields and 790−1,430 mm in aerobic fields. On average, aerobic fields used 190 mm less water in land preparation and had 250−300 mm less seepage and percolation, 80 mm less evaporation, and 25 mm less transpiration than flooded fields.

Practical implementation. Before sowing, the land should be dry prepared by plowing and harrowing to obtain a smooth seedbed. Seeds should be dry seeded at 1−2-cm depth in heavy (clayey) soils and at 2−3-cm depth in light-textured (loamy) soils. Sowing of the seeds can be done manually (e.g., dibbling the seeds in slits opened by a stick or a tooth harrow) or using direct-seeding machinery. If the crop is grown in a dry season, a light irrigation application (say 30 mm) should be given after sowing to promote emergence. Subsequent irrigation applications should aim to frequently restore the soil water content to field capacity, and depend on the rainfall pattern, the depth of groundwater, and on availability and/or cost of irrigation water. Irrigation can be applied by the same means as used for upland crops: flash flood, furrow, or sprinkler.

Tropical aerobic rice systems for water-short irrigated environments are still in the research and development phase. More research is especially needed to develop high-yielding aerobic rice.

9.5. Raised bedsOne of the recently proposed innovations to deal with water scarcity in the rice-wheat system in the Indo-Gangetic Plain is the use of raised beds, inspired by the success of the system in high-yielding, irrigated wheat-maize areas in Mexico. In the system of raised beds, rice is grown on beds that are separated by furrows through which irrigation water is coursed. In irrigation engineering terms, the system of raised beds is comparable with “furrow irrigation.” Irrigation is intermittent and the soil of the beds is dominantly in aerobic conditions; hence, the system can be considered an aerobic rice system (this is different from the use of beds in heavy soils to maintain saturated soil conditions). In general, furrow irrigation is more water efficient than flashflooding (depending on soil type, field dimensions, and slope of the land), and furrow irrigation should hold promise for aerobic rice.

Among the suggested benefits of raised beds are improved water-use and nutrient-use efficiency, improved water management, higher yields, and – when the operations are mechanized – reduced labor requirements and improved seeding and weeding practices. The main disadvantages of this system are generally lower yields



CROPS: RICEcompared to puddled transplanted rice, with serious problems of iron deficiency, weeds, accurate sowing depth, and sometimes nematodes.

Practical implementation. Growing rice on raised beds shows promise but is still in its infancy of development. Tractor-pulled equipment has been developed that shapes the beds and drills seed (sometimes together with fertilizers) in one operation. Rice can be transplanted or direct-seeded on the beds. So far, the raised-bed system has mostly been tested with current lowland rice varieties, and yield gains can be expected when suitable aerobic varieties are developed/used.

9.6. Conservation farmingWith aerobic rice, technologies of conservation agriculture, such as mulching and zero- or minimum tillage as practiced in upland crops, become available to rice farmers as well. Various methods of mulching (e.g., using dry soil, straw, and plastic sheets) are being experimented with in non-flooded rice systems in China and have been shown to reduce evaporation as well as percolation losses while maintaining high yields. In hilly areas in Shiyan, Hubei Province, in China, farmers are adopting the use of plastic sheets to cover rice fields in which the soil is kept just below saturation.

The proclaimed advantages are earlier crop establishment by 3 weeks (rice is established in early spring when temperatures are still low, and the plastic sheets increase the soil temperature), higher yields, less weed growth, and less water use (important during dry spells). However, little research has been done to verify these benefits. The leftover plastic after harvest may cause environmental degradation if not properly taken care of.

9.7. What option where?With absolute, or physical, water scarcity, farmers have little choice but to adapt to receiving less water than they would need to keep their fields continuously flooded. Figure 46 presents a gradient in relative water availability and some appropriate response options. On the far right-hand side of the (horizontal) water axis, water is amply available and farmers can practice continuous flooding of lowland rice and obtain the highest yields. On the far left-hand side, water is extremely short, such as in rainfed uplands, and yields are very low. Going from right to left along the water-availabilityaxis, water gets increasingly scarce and yields will decline.

14.6. ábra - Figure 46. Yield responses to water availability and soil condition in different rice production systems(Source: Slaton (ed), 2006)

(AWD = alternate wetting and drying, SSC = saturated soil culture, FC = field capacity, S = saturation point, ΔY = change in yield)

10. SustainabilityWhile relatively much work has been done on the development of technologies to maintain crop productivity



CROPS: RICEunder water scarcity, little research has been done on their long-term sustainability and environmental impacts.

Given assured water supply, lowland rice fields are extremely sustainable and able to produce continuously high yields, even under continuous double or triple cropping each year. Flooding of rice fields has beneficial effects on soil acidity (pH); soil organic matter buildup; phosphorus, iron, and zinc availability; and biological N fixation that supplies the crop with additional N.

When fields cannot be continuously flooded any more because of water scarcity, these beneficial effects gradually disappear. A change to more aerobic soil conditions (such as in AWD and aerobic rice) will negatively affect the soil pH in some situations and decrease the availability of phosphorus, iron, and zinc. Under the “safe AWD” practice, these problems do not occur, but, when more severe forms of AWD are implemented, they may start to occur.

Under fully aerobic conditions, whether on flat land or on raised beds, problems with micronutrient deficiencies have been observed. The introduction of aerobic phases in rice fields may also decrease the soil organic carbon content.

There are indications that soil-borne pests and diseases such as nematodes, root aphids, and fungi occur more in non-flooded rice systems than in flooded rice systems. Always, nematodes were found when yield failures were observed, sometimes aggravated by the presence of root aphids, fungi, and/or nutrient disorders. Crop rotation is necessary under such conditions, and breeders are trying to develop aerobic rice varieties with tolerance of these soil sicknesses.

11. Environmental impactsThe production of lowland rice affects the environment in negative ways, such as the emission

of greenhouse gases and water pollution. In this paragraph, environmental impacts that have a relationship with water and the hydrology of rice fields are summarized.

11.1. Ammonia volatilizationAmmonia (NH3) volatilization from urea fertilizer is the major pathway of N loss in tropical flooded rice fields, often causing losses of 50% or more of the applied urea-N. The magnitude of ammonia volatilization largely depends on climatic conditions, field water status, and the method of N fertilizer application. Volatilized ammonium can be deposited on the earth by rain, which can lead to soil acidification and unintended N inputs into natural ecosystems.

11.2. Greenhouse gasesIrrigated rice systems are a significant sink for atmospheric CO 2, a significant source of methane (CH4), and a small source of nitrous oxide (N2O). Recent measurements, however, show that many rice fields emit substantially less than those investigated in the early 1980s, especially in northern India and China. Also, methane emissions have actually decreased since the early 1980s because of changes in crop management such as a decreased use of organic inputs. The magnitude of methane emissions from rice fields is mainly determined by water regime and organic inputs and to a lesser extent by soil type, weather, tillage, residue management, fertilizer use, and rice cultivar. Flooding of the soil is a prerequisite for sustained emissions of methane. Mid-season drainage, a common irrigation practice adopted in major rice-growing regions in China and Japan, greatly reduces methane emissions. Similarly, rice environments with an uneven supply of water (for example, those suffering from water scarcity) have a lower emission potential than fully irrigated rice.

In irrigated rice systems with good water control, nitrous oxide emissions are quite small except when excessively high fertilizer-N rates are applied. In irrigated rice fields, nitrous oxide emissions mainly occur during fallow periods and immediately after flooding of the soil at the end of the fallow period.

11.3. Water pollutionChanges in water quality associated with rice production may be positive or negative, depending mainly on management practices such as fertilization and biocide (all chemicals used for crop protection, such as herbicides, pesticides, fungicides, etc.) use.



CROPS: RICEHigh nitrogen pollution of surface fresh waters can be found in rice-growing regions where fertilizer rates are excessively high.

Contamination of groundwater may arise from the leaching of nitrate or biocides and their residues. Nitrate leaching from flooded rice fields is quite negligible because of rapid denitrification under anaerobic conditions.

In traditional rice systems, relatively few herbicides are used as puddling, transplanting, and the ponding of water are effective weed control measures. In the warm and humid conditions of the tropics, volatilization is a major process of biocide loss, especially when biocides are applied on the surface of water or on wet soil. The relatively high temperatures further favor rapid transformation of the remaining biocides by (photo)chemical and microbial degradation, but little is known about the toxicity of the residues. As for nitrogen, however, biocides and their residues may be directly transferred to open water bodies through drainage water flowing overland out of rice fields. The potential for water pollution by biocides is greatly affected by field water management.

11.4. Effects of water scarcityWater scarcity affects not only the ability of rice fields to produce food but also the environment and the other ecosystem services of rice fields. Increasing water scarcity is expected to shift rice production to more water-abundant delta areas, and to lead to less flooded conditions in rice fields and to the introduction of upland crops that do not require flooding. These changes will have environmental consequences and will affect the traditional ecosystem services of the rice landscape.

Rice that is not permanently flooded tends to have more weed growth and a broader weed spectrum than rice that is permanently flooded. It is expected that water shortages will lead to more frequent use of herbicides, which may increase the environmental load of herbicide residues. With less water, the numbers and types of pests and predators (e.g., spiders) may change as well as predator-pest relationships. The possible shift in the use of pesticides by farmers in response to these changes, and what this means for the environment, is as yet unknown. More leaching of nitrate is expected with increased soil aeration (either with growing rice under non-flooded conditions, or with the shift to upland crops) than under flooded conditions. Less methane emissions are expected under aerobic conditions than under flooded conditions, but higher nitrous oxide emissions are expected. However, the relative emissions of these greenhouse gases vary with environment and management practices. Flooded rice is effective in leaching accumulated salts from the soil profile, and the change to more aerobic conditions may result in increased salinization.

12. Summary• Rice is unique among the major food crops in its ability to grow in a wide range of hydrological situations,

soil types, and climates. Rice is the only cereal that can grow in wetland conditions.

• Worldwide, there are about 150 million hectares of rice land, which provide around 550–600 million tons of rough rice annually. About 79 million ha of irrigated lowlands provide 75% of the total world rice production.

• Lowland rice is traditionally grown in bunded fields that are continuously flooded from crop establishment to close to harvest. It is estimated that irrigated lowland rice receives some 34–43% of the total world’s irrigation water, or 24–30% of the total world’s freshwater withdrawals.

• By 2025, 15-20 million hectares of irrigated rice may suffer water scarcity. With increasing water scarcity, the sustainability, food production, and ecosystem services of rice fields are threatened.

• Therefore, care must be taken to use water wisely and reduce water losses from rice fields. There is a need to develop and disseminate water management practices that can help farmers to cope with water scarcity in irrigated environments.


15. fejezet - 15. IRRIGATION MANAGEMENT OF MAIN CROPS: COTTON1. Climate requirementsThe development of the crop is sensitive to temperature. Cool nights and low daytime temperatures result in vegetative growth with few fruiting branches. The crop is very sensitive to frost and a minimum of 200 frost-free days is required. The length of the total growing period is about 150 to 180 days. Depending on temperature and variety, 50 to 85 days are required from planting to first bud formation, 25 to 30 days for flower formation and 50 to 60 days from flower opening to mature boll. Cotton is a short-day plant but day-neutral varieties exist. However, the effect of day length on flowering is influenced by temperature. Germination is optimum at temperatures of 18 to 30 °C, with minimum of 14 °C and maximum of 40 °C.

Delayed germination exposes seeds to fungus infections in the soil. For early vegetative growth, temperature must exceed 20 °C with 30 °C as desirable. For proper bud formation and flowering, daytime temperature should be higher than 20 °C and night temperature higher than 12 °C, but should not exceed 40 and 27 °C respectively. Temperatures between 27 and 32 °C are optimum for boll development and maturation but above 38 °C yields are reduced. Strong and/or cold winds seriously affect the delicate young seedlings and at maturity will blow away fiber from opened bolls and cause soiling of the fiber with dust. Continuous rain during flowering and boll opening will impair pollination and reduce fiber quality. Heavy rainfall during flowering causes flower buds and young bolls to fall.

2. Soil requirementsCotton is grown on a wide range of soils but medium and heavy textured, deep, well drained, fertile clayey, alluvial, chernozem and laterite soils with good water holding characteristics are preferred. Acid or dense sub soils limit root penetration. The pH range is 5.5 to 8 with 7 to 8 regarded as optimum.

3. Cotton rooting characteristics and available soil waterMaximum depth of the cotton rooting system can be achieved relatively quickly, it may be normally reached within 40 to 60 days after planting (Figure 47). Lateral roots continue to grow throughout the rooting profile. This is why final size of the root system may not be reached until 90 days after planting.

If root development is not limited by soil compaction or lack of water, cotton roots can penetrate up to 90 cm, but the most active root zone can be found in the top 60 cm. Irrigation timing and amount should be based on the soil moisture depletion in the top 60 cm, because the moisture level should change little during irrigation below 60 cm depth.

15.1. ábra - Figure 47. Development of cotton rooting system



CROPS: COTTON

(Source: Cotton Production Manual, Netafim, USA)

(Author’s note: 1 (inch) = 2.54 cm)

To provide a safety factor, cotton irrigation scheduling is designed around “easily available water” which, as a rule of thumb, is assumed to be about 50% of the total available water. This is referred to as the limit of allowable depletion before an irrigation event must be triggered. Soil properties determine the limits of when to irrigate and how much to apply. Cotton must be irrigated when no more than 50% of the available water has been depleted. An allowable depletion of 50% is the maximum limit before an irrigation event must be triggered or there may be loss of yield. The amount of water to apply is the amount required to fill the soil reservoir to field capacity. Table 27 summarizes typical quantities of available water and allowable depletion for various soil types and for a rooting depth of 60 cm.

15.2. ábra - Table 27. Soil texture-based estimation of total available water and net water amounts per irrigation event during the cotton growing season

4. Crop water use



CROPS: COTTONFor high yields, the seasonal crop water requirements for cotton were estimated to be 350 to 900 mm per hectare under range of climatic conditions and varying length of growing season (150-210 days) with an average daily evapotranspiration rate of 4 to 8 mm per day.

A cotton crop’s requirement for water changes throughout the growing season, following the pattern of evapotranspiration. Figure 48 represents a water use (crop evapotranspiration) curve showing the seasonal water use characteristics of cotton at essential growth stages.

15.3. ábra - Figure 48. Seasonal daily water use for cotton production

(Source: modified from Gibb et al., 2012)

The rate of evapotranspiration is determined primarily by meteorological factors and the availability of soil water. Total crop evapotranspiration will vary with canopy size, or leaf area. Daily water use is expressed as a function of days past planting. Water use was observed to increase steadily from planting to first open boll with a peak of between 8 and 10 mm and tended to decline slightly afterward. This suggests the need of maintaining well-watered field conditions until the first open boll. At about 60% boll opening, water use tends to substantially decline.

5. Water sensitivity of cotton growth stagesIrrigation alleviates the detrimental impact of soil water deficit stress on two diverse physiologicalprocesses in plants that occur when they cannot get enough water. The most sensitive physiological process in plants to water deficit stress is cell growth. From root tips expanding through the soil to fibers elongating on seedcoats, the ability of individual cells within a plant to expand is largely determined by the availability of soil water. Along with reducing growth, soil water deficit stress triggers hormonal changes in reproductive growth that results in the shedding of fruiting structures (squares and bolls). Irrigation management should be aimed at reducing stress at critical times so the plants are provided the greatest ability to initiate, retain, and mature bolls.

The degree of plant response to stress will vary depending on the level of stress, which occurs and the timing at which the stress is imposed, relative to crop growth. Table 28 summarises the plant’s responses to differing degrees of water stress. The effects on final crop yield, fibre development, maturity and water use efficiency are also discussed.

Maximum demand for water coincides with the growth period between peak flowering and early boll development. Exposing the plant to water stress at this stage of growth can result in significant yield reductions. The impact of water stress at different crop growth stages on final yield is directly related to the water demands expressed by the crop. Stress during periods of high water demand can produce large reductions in yield. Stress during peak flowering can double yield losses compared with early or late seasonal stress. The impact of any one stress period is increased if followed by further stress.

15.1. táblázat - Table 28. Cotton’s responses to differing degrees of water stress (Source: modified from Gibb et al., 2012)



CROPS: COTTON

Water stress level

Possible causes Plant responses Yield effects on maturity and WUE

Minimal Reduced irrigation deficit

Excessive rainfall

Cloudy weather

Excessive early insect damage

High plant stands

Excessive vegetative growth Increase in leaf area

Extended flowering cycle

Reduced carbohydrate surplus for bolls

Reduced root development

High boll capacity but poor boll retention

Reduced yield

Reduced boll size

Delayed maturity

Normal fibre length but low micronaire

Poor WUE

Mild Optimum irrigation deficit

Average temperatures (not excessively hot)

Optimum vegetative growth rate

Leaf expansion restricted

Photosynthesis remains unaffected

Maximum carbohydrate surplus

Maximum boll development

Good fibre development

Maximum yield

High quality cotton

No delay in maturity

Maximum WUE

Moderate Increased irrigation deficit

Extremely hot temperatures with low humidity

Windy conditions

Little cloud cover

Reduced vegetative growth and leaf expansion

Reduced photosynthesis

Reduced surplus carbohydrates

Reduced boll carrying capacity

Increased fibre development

Reduced yield

Early maturity

Increased short fibre micronaire

Slight decrease in WUE

Severe Less than 3 irrigations

Dryland crops

Vegetative growth greatly reduced - stops after flowering

Greatly reduced carrying capacity

Little surplus carbohydrates

Low boll retention

Low yields

Short fibre

High or low micronaire depending on stress pattern

WUE depends on rainfall

5.1. Planting to EmergenceWater is critical for germination and irrigating at this stage is primarily for stand establishment. If the seedbed is dry and irrigation is needed to establish a stand, it is preferable to irrigate before planting. Pre-irrigation reduces the possibility of seedling disease compared to irrigating shortly after planting. In addition, irrigating after planting will cool the soil and may reduce seedling growth rates. Once the seeds germinate, sufficient moisture must be in close proximity of the seedling until sufficient roots are developed to increase the area of water uptake. Establishment of the root system is quite fast, with taproots growing up to 6 cm per day after they



CROPS: COTTONemerge from the seed.

5.2. Emergence to First SquareEarly season water deficit after stand establishment is often not an issue if there is adequate water for emergence and early seedling development. Water demand at this time is low and young cotton plants partition significant resources to the roots. Unless soil water deficit is extremely severe, irrigation at this time contributes relatively little to yield.

In fact, a mild water deficit early in the season can stimulate root production, especially encouraging deeper root systems. Primed Acclimation (PA) is an irrigation concept that uses intentional mild drought stress during early vegetative development to induce physiological changes in the plant that make it more drought tolerant during mid-season, when detrimental effects of water stress are maximal. As the name implies, a time of mild, controlled water deficit acclimates plants to water scarce conditions; thereby beginning (or priming) a cascade of plant responses that increases water-use efficiency. Some of these changes include increased root growth, decreased water-use, changes in fruiting patterns, and elicited molecular/enzymatic responses. PA can maintain yield with significant water reduction.

For cotton, the PA period lasts about 35 days, starting at full stand establishment (~14 days after planting) to late squaring/first bloom. During this period, water may be reduced by as much as 30% with no yield loss in some southern production regions. An additional benefit to properly applied PA is a reduction in plant growth regulator needed later in the growing season and a more uniform maturity.

5.3. First Square to First FlowerThe approximate 21 days from first square to first bloom is a critical time for avoiding severe waterdeficit stress. During this period, cotton vegetative growth is very rapid and the number of potential fruiting sites for the crop is determined, especially in short season environments. This is also the period when plants are most rapidly taking up phosphorus and potassium from the soil because of rapid root growth. There is evidence from field-based imaging and measurements of cotton root systems that the maximum depth of the rooting system can be achieved relatively quickly and often exceeds 90 cm in depth. Maximum depths may be reached within 40 to 60 days after planting. Severe water deficit stress during this period is especially damaging to the cotton crop in short-season environments.

5.4. First Flower to Peak BloomWater deficit stress early in this growth stage reduces plant growth which reduces the number of fruiting sites that are initiated. In addition, severe water deficit stress can also reduce boll number through shedding of young bolls and results in substantial yield loss. During early bloom, squares are generally not lost due to water deficit stress, so if square shedding is observed, other causes should be investigated. Water deficit stress at this time also impacts yield by reducing the size of surviving bolls. Severe stress reduces fiber quality through shorter staple and higher micronaire.

At this growth stage, maximum rooting depth is achieved but lateral roots continue to grow throughout the rooting profile so that the final size of the root system may not be reached until 90 days after planting.

5.5. Peak Bloom to Open BollsWater deficit stress during this growth stage is less critical than during squaring and early flowering. Water stress during this period can result in square and young boll shedding. However, these losses of late fruit have less impact on yield than loss of early season bolls. Fiber quality parameters affected by stress at this time are fiber length and micronaire, particularly in the young bolls.

After bolls start opening, plants should be allowed to become water stressed to allow for better harvest conditions. Stress at this time hastens boll opening, makes defoliation easier, and reduces regrowth.

6. Management Considerations for Irrigated Cotton6.1. Cotton growth and irrigation management



CROPS: COTTONIrrigation brings a set of management challenges and opportunities. In general, irrigated fields require more intensive management, not only due to the need to schedule irrigation, but also due to the ability to manage water stress in the field. Early season irrigation can reduce soil crusting and improve plant stands. Also, as discussed in paragraph 15, careful control of water stress early in the season can reduce the need for plant growth regulators later in the season. It should be noted that, in general, irrigation will increase yield potential, so fertilizer requirements will also tend to increase, particularly nitrogen.

An advantage of irrigation not commonly considered is the ability to activate herbicides after application. With herbicide-resistant weeds, timely activation of residual herbicides can be guaranteed with pivot irrigation systems. This can also apply to fertilizer applications, especially side-dressed nitrogen. With the proper equipment, irrigation can also be used to deliver fertilizers and some crop production products.

The Table 29 identifies the uses and risks of irrigation during the growing season and is expanded upon in each of the following paragraphs.

15.2. táblázat - Table 29. Benefits and risks of irrigation during cotton growing season (Source: Perry and Barnes (eds), 2012)

Crop Stage Sensitivity to Water Deficit Stress

Benefits Detriments

Emergence Moderate Activate herbicides

Hydrate germinating plants

Cool surface soil

Seedling disease if cool

Create soil crusts

Herbicide injury

Pre-Squaring Slight Few unless extreme drought Shallow root system

Squaring Moderate Avoid subsoil water loss

Build plant size

Brings fertilizers into solution

Soil saturation

Excessive vegetation

Early Bloom High Retain bolls

New fruit and leaves

Compensate for nematodes, compaction, herbicide injury

High fiber quality

Few

Late Bloom Moderate Retain bolls

Healthy leaves

High fiber quality

Few

Cutout Slight Healthy leaves Delay maturity

Opening None Few Boll rot, delayed harvest

6.2. Germination and Seedling EmergenceSeedbed moisture is essential for germination and emergence. Pivot sprinkler irrigation can enhance these processes by providing moisture for root and hypocotyl expansion, by softening surface crusts and by cooling



CROPS: COTTONthe surface of sandy soils during periods of extreme heat. Frequent and small (6 to 12 mm) irrigations are appropriate when the weather is hot but should be avoided when the weather cools and are not usually necessary after full seedling emergence. Irrigating emerging and seedling cotton during cool weather promotes seedling disease. Pivot sprinkler irrigation is also highly useful in activating pre-emergence herbicides. Typically, 5 to 20 mm is sufficient to move pre-emergent herbicides into the soil where they are protected against photo degradation and are activated to control germinating weeds. Unfortunately, frequent rain or irrigation can also move herbicides into cotton’s root zone, causing phytotoxicity.

Row watering planted but not emerged cotton fields is difficult unless water control, bed shape and field slope allow subbing into the planted zone with overtopping the beds.

6.3. Pre-Squaring CottonIrrigation is rarely needed in Mid-South and Southeast cotton during the pre-squaring period, although irrigation could alleviate stress during severe hot and dry periods. During the pre-squaring period roots are expanding into new soil at over twice the rate that shoots are expanding, and in most fields are able to provide sufficient water to support maximum seedling growth of the small leaf area. Frequent irrigation prior to bloom may limit the rooting depth by restricting soil oxygen or by promoting shallow root. Roots proliferate in soil favorable for growth (i.e., warm, moist, friable, non-toxic, and containing sufficient oxygen and nutrients). If these conditions are maintained near the soil surface then root expansion in the subsoil will be limited and the plant will be vulnerable to periodic drought during the bloom phase.

6.4. Squaring CottonDuring the squaring period, the root volume and most of the harvestable fruiting sites are created. Plant stress during this period can limit both of these and place an upper limit on yield, especially for earlier maturing varieties that tend to set a larger proportion of fruit on lower nodes, and are thereby less likely to recover from stress. Severe water-deficit stress, to the point of plant wilting, should be avoided during this period. In sandy or low-water infiltration fields with limited irrigation capacity, care should also be given to avoid depleting subsoil moisture reserves that will be needed during the bloom period. Varietals and season length differences should also be considered in water management of squaring cotton. Water deficit stress during the squaring period is more injurious to the yield of early maturing and more determinate varieties in long growing seasons. Excess water, and lack of soil oxygen, is a more likely problem during squaring than water deficit stress, since the limited plant size and cooler temperature restricts water use. If surface soils remain saturated for an extended period, plant growth is curtailed and fruit may be shed.

6.5. Early Bloom CottonDuring this period, daily water use, daily fertilizer use, and sensitivity to water-deficit stress all increase. Retention of small bolls (less than 2 cm) is the most sensitive crop stage to water-deficit stress such that the key yield-enhancing benefit of irrigation is to avoid water-deficit stress during bloom. A secondary benefit is the quick activation and/or delivery of nitrogen fertilizer to under-fertilized cotton fields. Although sprinkling during the morning hours will cause some pollen rupture reducing seed set, boll size, and boll retention when water contacts open blooms prior to midday, this detrimental impact has been shown to be slight compared to the benefit of maintaining a healthy photosynthetic capability and sustaining new leaves, new squares and new bolls. Where shallow soils, acid soils, nematodes or compaction limit root function, maintaining ample soil water during early bloom is essential for high yields.

6.6. Cutout, Late Bloom and Boll Opening CottonOnce cotton has reached cutout or the last effective bloom date, water deficit stress can usually be increased gradually such that new vegetative growth is curtailed but healthy turgid (non-wilting) leaves are maintained until over half of the bolls are mature. Irrigation interval and soil moisture deficit should be increased during this period to minimize the cooling associated with evaporation and to prevent waterlogging under rainy conditions. Avoiding irrigation when bolls start to open will lessen canopy humidity and resultant boll rot or hard lock. A dry surface and subsoil also facilitates soil surface drainage, which minimizes harvest delays and soil compaction from field traffic after heavy rains.

6.7. Irrigation adds flexibility to farming operations



CROPS: COTTONCotton growers now manage anywhere from a few hundred to a few thousand hectares. Due to equipment limitations, a grower cannot plant all hectares at a single time, much less plant significant fields immediately after a rain. Irrigation is critical when planting into limited soil moisture during hot, dry weather. Having irrigation capacity on some fields allows for a larger proportion of dryland hectares to be planted soon after a rainfall event, while the irrigated areas can be planted at any time. For late-planted or double-cropped cotton (generally cotton planted behind wheat), immediate emergence and rapid seedling growth is critical and days lost while waiting on a rain will invariably reduce yield. Additionally, irrigation enables producers to develop and retain the earliest set bolls, which boost yield in a compressed season often observed in later-planted cotton.

6.8. Irrigation and Variety SelectionAnother management consideration for irrigating cotton includes variety selection and positioning. Modern cotton varieties vary widely with regard to maturity, boll distribution, drought tolerance, need for growth regulation, and yield response to irrigation. Although most, if not all, cotton varieties respond positively to supplemental irrigation when encountering dry weather, some varieties respond differently to increased irrigation rates or to deficit irrigation. Research has shown that some varieties (primarily later-maturing varieties or ones with drought-tolerant characteristics) show little to no yield penalty associated with deficit irrigation unless extreme high temperatures and prolonged drought occurs. In contrast, other varieties (typically earlier maturing varieties that set a higher proportion of bolls on lower nodes) are touted to respond to greater amounts of applied water. With the variation between cotton varieties in their yield response and growth characteristics to water, growers can position varieties into appropriate fields and environments. Later-maturing varieties or those that are less injured by water-deficit stress are ideally positioned into fields with reduced irrigation capacity (large pivots, restricted application amounts, severe runoff, low water-holding capacity soils) while varieties that set bolls lower on the plant can be positioned into fields with greater irrigation capacity.

7. Cotton irrigation schedulingThe goal of irrigation scheduling is to determine an irrigation duration and frequency that keeps the root zone below fieldcapacity and above the allowable depletion. At this point, the crops roots are exposed to an ample supply of easily available water with sufficient oxygen to promote healthy root growth.

Two principle methods are used to schedule irrigations in cotton fields. One method is called water budgeting or ‘checkbook’ method and it involves estimating crop water needs based on the evaporative demand of the environment; the other technique relies on soil-based measurements. Both methods have their limitations. The water budgeting method looks at gross water demand and does not specifically look at your crop or soil. Factors are used to adjust for your specific growing conditions. The measurement of soil moisture is limited to the specific areas where measurement devices are placed. If the location of the devise is not representative of the entire field, the information can be misleading. The best approach is use a combination of both techniques. Most commonly, irrigations are scheduled using water budgeting and verified by measuring soil moisture at select points in the field.

7.1. Water budgetingWater budgeting involves tracking additions and losses and balancing them. The losses are due to crop water use, any leach requirements and inefficiencies in the irrigation system. The additions are due to irrigation and rainfall. The objective of the water budget method is to maintain soil moisture near the optimum level by keeping track of crop water use and then irrigating to replace the water used. Knowledge of crop water use is essential to using the water budget approach.

There are many freely available irrigation scheduling tools that predict when to irrigate based on weather and crop conditions. Most water-balance, irrigation-scheduling programs function in a similar manner, but the means of data input and the representation of the output can be very different.

The Mississippi Irrigation Scheduling Tool (MIST) relies on the most current scientific knowledge of crop water use to assist producers in making irrigation decisions. MIST automatically collects weather and soil information from national and regional databases and continuously calculates crop water use. No soil or plant measurements are required to run the scheduler. Automatically downloading information from these databases allows growers to use MIST, without requiring extensive data collection or input to the model.

With MIST, there are no programs to install or maintain. The program is accessed through the internet, and is



CROPS: COTTONavailable on several platforms, including smart phones, tablet computers, laptops, and desktop computers. This allows the user to determine crop water needs from any location, and instantly tell when a crop needs water. Using a daily time-step for calculations and weather updates allows a more accurate determination of soil available water. Use of a daily time step also allows calculations to determine future crop water needs over the next several days, allowing growers tomanage their water resources better. MIST indicates when an irrigation is needed based on the soil type, weather conditions, and capacity of the irrigation system.

The Management Of Irrigation Systems in Tennessee (MOIST) program from the University of Tennessee requires weekly input of rainfall and irrigation instead of daily data. This is easier for producers to maintain and thus keep track of the needed rainfall and irrigation amounts. The approach works fine for the more drought-tolerant row crops that are grown in the good water-holding soils; however, weekly input may not be adequate for water-sensitive crops grown in low water-holding soils like sands.

Water balance programs are great irrigation scheduling tools because they predict water use on a whole field basis and are not particular to one small location in a field when a crop is adequately watered. A producer should always feel confident that they know how much water is needed to replace the water being used by their crop when using a water balance approach. However, there are some limitations that one should be aware of. For instance, most water balance programs assume that excess water in a soil quickly drains to field capacity and this is not true of all soils. Also, there can be run-off from intense rainfall events and if the entire rainfall amount is entered into the program, a water balance approach will not automatically recognize that the entire rainfall amount did not enter the soil profile. Combining soil moisture monitoring with a water balance approach can avoid these pitfalls.

7.2. Sensor-Based SchedulingThere are a number of sensor systems now available that provide valuable information on when a cotton field is ready to be irrigated. Wireless data transmission and improved software interfaces are now making these sensors practical for farm use. There are three different physical properties measured by sensors often used to determine when to irrigate cotton:

• Soil matric potential. Sensors that measure matric potential include: tensiometers and resistance sensor blocks.

• Volumetric moisture content. There are several types of sensors that measure this property including capacitance sensors, time domain reflectometry (TDR) and frequency domain reflectometry (FDR) sensors, and neutron probes.

• Canopy temperature. It is most commonly measured with an infrared thermometer .

The tensiometer may have limited usefulness in cotton irrigation scheduling. It is one of our most accurate tools but has a very limited range of measurement (wet readings only) while cotton is fairly drought tolerant and often the soil is allowed to dry to a point where the tensiometer will break tension. An exception would be soils like loamy sands that require frequent watering and hold a majority of their available water in large pores at low tension. All the other sensor types have sufficient range for cotton irrigation, but soil type can still impact sensor performance.

The tensiometer and granular matrix sensor need to maintain hydraulic contact with the soil so that water can move in and out of the sensors. In very coarse sands, the hydraulic conductivity becomes very low as the soil dries, and thus water can no longer move in and out of the sensor. This condition can be corrected by adding a porous material around the sensor that creates better contact. Also, clay soils that crack can break hydraulic contact in these sensors. These same cracking clays will cause difficulty with sensors that measure dielectric constant because air gaps next to the sensor will greatly change the measurement.

In arid regions, canopy temperature is a good tool for cotton irrigation management. Canopy temperature is a little complicated to interpret into an irrigation management decision, especially in humid regions. When the air is moist (high relative humidity), the amount of evaporative cooling is reduced even for well-watered cotton. Research is still in process to determine the appropriate use of canopy temperature for cotton grown in humid regions.

By and large, we have a variety of soil sensors that will work for cotton irrigation scheduling under most conditions.



CROPS: COTTON

7.3. Specific irrigation recommendations for cottonThe recommendation described here based on using subsurface drip irrigation (SDI) system. It is always best to start the growing season with a full soil profile. This can be from rainfall or pre-irrigation. This makes it easier for the grower to maintain optimum growing moisture with less stress of either over irrigating or under irrigating. It is always the best to establish the plants water needs by stages of growth and or water sensing devices such as tensiometers or other similar equipment. You can also get access to Pan Evaporation and Potential Evapotransporation (PET) from local universities or web sites. The cotton’s water requirements will increase as it accumulates biomass, (taller plants demand more water). Avoiding water stress at the beginning of first square is critical in establishing adequate plant structure to facilitate yield goals. The growth rate is represented by the internodes length. From first square to peak bloom the internodes length needs to be 4-5 cm. If it is over 5 cm the plant is getting excess water or fertilizer. If the internodes are less than 2.5 cm the plant is under stress.

The irrigation needs to be based on a weekly program:

• Germination to first square: irrigate only to maintain growth and or as a carrier of nutrients. Water use is very low at this time, large volume of water is not needed. Irrigating too early can increase potential for exposure to waterlogging. Irrigating too late will incur yield penalties due to the impact of stress on plant development.

• 1st Square – replace 30-35% of PET. Keep internodes length to 4-5 cm, add 5% per week for 4 weeks. This may vary upon regional climates. An area of higher relative humidity might reduce this amount some according to internodes length. Be timely with your irrigations. Once this stage begins, do not let the plants stress.

• 1st Flower – 50-55% PET. Add 10% per week for 4 weeks. Again, watch petiole reports, internodes lengths, fruit set, and cloudy weather and adjust if necessary. Manage weed populations in order to maximize water and fertilizer.

• Peak Bloom – 90-95 % PET. This might be adjusted downward if the cotton has closed furrows and is holding moisture in the canopy. Also look for moisture surfacing in the furrow. If this occurs, cut back on the time of irrigation and increase frequencies.

• If you have kept your moisture levels at optimum you can cut back 10% per week for three weeks to finish the cotton.

Deciding when to terminate irrigation

It is approaching the time when cotton producers must decide when to terminate irrigation. This decision is generally based upon two primary factors, cotton growth stage and amount of water currently in the soil:

• As flowering approaches the top of the plant, the plant finally puts most of its energy into boll development, flowering virtually ceases, and plants are considered to have reached the “cut-out” growth stage. This generally occurs at 4 to 5 NAWF (“Nodes Above White Flower”).

• Depending upon the number of heat units available, generally it can take 50 to 60 days for this last white flower (last effective flower) to make a mature boll. Ideally, at that time, this boll (and all those below it) would be mature enough to allow timely defoliation/desiccation without significant yield loss.

• Irrigation, if needed to ensure continued boll development, should be scheduled to provide enough water to carry these bolls to maturity, and not have a significant amount remaining in the soil after harvest. Therefore, irrigation is required for the first 20-25 days after last effective flower (until cotton is at 25-50% open bole). After that time, crop should be able to rely on stored soil water for the last 25-30 days.

A quick way for the producer to get a good estimation of boll maturity is to use the “knife” technique. A mature green boll will be extremely difficult to cut open, even with a very sharp knife; the seed within the boll will have a tan color, and it will be very difficult to dent the boll by pressing it with your fingers. An immature boll can be easily cut with a sharp knife, the seed coat will have a milky white color, and the cotyledons will be white instead of green.

8. Irrigation and cotton disease interactions



CROPS: COTTONPlant diseases are usually a problem created by human activity. Irrigated cotton farming systems generally favour the survival and dispersal of the pathogens that cause diseases of cotton and often provide environments conducive to infection.

Irrigation strategies have contributed, and are still contributing, to the emergence of significant cotton disease problems that threaten the economic viability of cotton farming. Cotton plant breeders may eventually provide solutions to these disease problems in the form of resistant varieties but it could be a long time before that solution is forthcoming. In the meantime it is essential that growers do all they can to slow the rate of epidemic development by reducing the spread of pathogens, providing for the adequate nutrition of the host and by manipulating the crop environment so that it is less favourable for disease development (Table 30).

15.3. táblázat - Table 30. Impact of irrigation practices on the crop environment (Source: own editing on the basis of Allen et al., 2012)

Irrigation impacts Diseases Recommended practices

Irrigations drop soil temperatures Seedling diseases (black root rot, fusarium and verticillium wilt)

Plant into moisture in preference

To watering-up

High humidity and periods of leaf wetness favour infection

Foliar pathogens (bacterial blight, alternaria leaf spot)

Avoid late irrigations

Late season irrigations contribute to later harvests

Incidence of verticillium wilt Avoid irrigation systems that wet the foliage

Tailwater recirculation with furrow irrigation

Infected crop residues in tailwater

Black root rot, fusarium and verticillium wilt

Consider buried drip instead of furrow irrigation

Remove crop residues from tailwater return systems

Minimise tailwater backing up into field

Diminished host plant resistance due to waterlogging-induced nutrient imbalances

Potassium deficiency in cotton has been associated with increased susceptibility to fusarium wilt, verticillium wilt and alternaria leaf spot

Avoid or minimise waterlogging

9. Evaluation of cotton irrigation systemsThere are many ways to deliver irrigation water to the field. The best system is field specific. There are several options for delivering irrigation water. The three major categories of irrigation systems are:

• Sprinkler irrigation systems – where center pivots are the type most commonly used for cotton production,

• Surface irrigation – applying the water down the furrow from siphon tubes or poly-pipe as well as flooding an irrigation basin,

• Drip irrigation – surface or subsurface.

Each of these systems is described shortly including with their advantages and disadvantages/risks in the following paragraphs. Many factors determine which is best for a particular field including soil type, field slope, field geometry, and water source (well capacity or surface water).



CROPS: COTTON

9.1. Subsurface Drip IrrigationSubsurface drip irrigation (SDI) is proving to be an economical method of water application to agronomic row crops such as corn, peanuts and cotton.

A subsurface drip irrigation system offers many advantages compared to other irrigation systems. There is less annual labor and an increased life expectancy; a dry soil surface reduces the occurrences of soil-borne diseases and helps to control weed infestations. The dry soil in furrow enhances trafficability and reduces soil compaction. There is a more efficient use of water and nutrients, and there is a significant improvement in yield and quality components.

SDI is normally defined as a “permanent” system, that is, the drip lines are not taken up every year. SDI systems must be carefully designed and installed so that they operate with proper efficiency and so that fertilizers and chemicals can be applied in a uniform and efficient manner.

Before the design of an SDI system is done, it must be determined that the intended site is suitable for SDI. These considerations include adequate water supply, acceptable water quality, and appropriate topography. Another consideration is management, which is important to all drip irrigation systems and especially important to SDI systems in which drip lines are below ground – out of sight.

The design of an SDI system is similar to the design of other drip irrigation systems, with additional consideration given to system flushing and traffic. Deep SDI systems have life spans much longer (15 to 20 years) than either surface drip or shallow subsurface drip (S3DI) and, therefore, need higher-quality filtration methods and flush systems. Aside from tubing, the major expenses for deep SDI are the required filtration and flush systems. Filtration can range from inexpensive manual to expensive electronic flush systems. These SDI systems need both input and flush mainline along with the associated valves and fittings. Installation will require heavier equipment and more labor.

9.2. Surface Drip IrrigationFor many years, surface drip irrigation has been used to irrigate high-value vegetable crops. In recent years, surface drip of row crops has been increasing throughout the world.

Surface drip irrigation can precisely deliver water and nutrients to the crop root zone. Surface drip irrigation systems save water by only wetting a small area of the overall soil surface, thus reducing evaporation. Additional advantages for surface drip irrigation include low application rates, precise water placement, and low operating pressures. Drip irrigation can also be used in irregularly shaped fields to maximize the irrigated acreage.

Disadvantages of surface drip irrigation include the initial cost of the system, specialized equipment to install and remove tubing, and the annual system component replacement. Without proper care, some irrigation system components can be damaged with machinery. Additionally, rodents and insects can create additional maintenance problems by chewing holes in the plastic tubing.

A typical surface drip irrigation system would consist of a pumping plant, pressure regulation, a filtration system, and a distribution system divided into zones delivering water to the drip tubing. A major consideration in design of surface drip irrigation systems is in the drip tubing lateral spacing. Typical lateral spacing for row crop production is for either 1) every row or 2) alternative row middles (see Figure 49). An advantage of alternative row spacing is the reduction in tubing cost and the ease of tubing removal.

15.4. ábra - Figure 49. Surface drip irrigation configurations for cotton



CROPS: COTTON

(Source: Perry and Barnes (eds), 2012)

In high-value crops, surface drip laterals are typically replaced with each crop. In some row crop production systems, annual tape replacement may be cost-prohibitive while other cropping systems may be quite cost-effective. Some researchers and manufacturers have developed methods to retrieve the drip tape after crop harvest and methods to repair damaged tape. If the cropping system is using strip tillage and GPS systems for planting operations, the tubing may be used for several years before retrieval and replacement are needed.

Shallow SubSurface Drip Irrigation

More recently, some researchers have started using shallow subsurface drip irrigation (S3DI). The S3DI is basically surface drip irrigation buried 5-10 cm into the soil in alternate row middles. This is much shallower than sub-subsurface drip irrigation (SDI), but can reduce the damage from rodents and insects.

Cost for surface drip and S3DI are similar and much less expensive than deeply buried subsurface drip systems. The costs of installation includes manual filtration, pressure regulation, tubing, fittings, valves and infield mainline. This expense does not include equipment, labor or water conveyance from water source to the field. These costs assume clean well water, smaller rectangular fields, and field lengths less than 215 m. With proper management, these systems can be maintained for 3 to 5 years depending on crop rotation.

9.3. Center PivotsCenter pivot sprinkler irrigation systems are among the most popular mechanical-move systems for applying irrigation water to field crops like cotton.

Since center pivot systems have low labor requirements, apply water very efficiently, can operate unattended for long periods, and now are being automated, they have proven to be very popular. Since the late 1970s, the use of such systems has grown rapidly.

Center pivot systems have many advantages and disadvantages over other irrigation application methods (Table 31).

15.4. táblázat - Table 31. Advantages and disadvantages of center pivot systems (Source: own editing on the basis of Perry and Barnes (eds), 2012)

Advantages Disadvantages

Potential for automated operation Relatively high initial cost

Simplified water delivery High application rates at outer end of lateral (causing runoff)

Ability to apply small irrigation depths Relatively high pipe-friction losses



CROPS: COTTON

Very high application uniformity Circular pattern not matching square fields (leaving dry corners)

Ability to improve irrigation management Topographic changes causing potential operating pressure variations

Ability to apply agri-chemicals (chemigation)

Ability to activate surface-applied agrichemicals

Little annual setup required

9.4. Surface Irrigation (Flood/Furrow)Surface irrigation is the oldest and most common form of irrigation Surface irrigation is a broad term applied to irrigation practices through which water is applied to the soil surface and flows gravimetrically across the soil surface.

The field in which surface irrigation will be applied must have a positive and continuous grade to facilitate water movement across the field and to prevent water retention. In order to facilitate surface irrigation, many producers perform earthmoving operations in order to gain a positive and continuous grade utilizing equipment supplied with real-time kinematic (RTK) global positioning systems (GPS). Grades should be a minimum of 0.1% and no more than 0.5%. Grades between 0.15% and 0.3% are considered optimum. Cotton growers typically plant on beds which run from the highest elevation point in the field to the lowest elevation point. Once the crop is established, irrigation water is typically introduced to the field through a pipe system from which irrigation water runs gravimetrically down the furrows to the end of the row. To a lesser extent, growers will plant cotton flat on precision-graded fields, introduce irrigation water at a central point, and allow it to flow freely across a given field.

10. Summary• Cotton is a drought- and heat-tolerant crop that does not requires excessive amounts of water to grow.

Cotton’s global water footprint is about 2.6% of the world’s water use, lower than maize 9%, wheat 12% and rice 21%.

• Almost half of the world cotton area has no assured irrigation water supply and depends on natural rainfall. Cotton requires about 610-660 mm of water during the growing season as rainfall or supplemental irrigation to produce about 750 kg lint/ha.

• Proper irrigation management is essential for cotton, and is used to balance vegetative growth with boll development, as well as to manage disease and insect populations.

• The delivery method, the number of applications, and the amount of applied surface water varies from location to location. Total applied water needs depend on the soil type, residual soil moisture and water availability.

• For cotton, furrow irrigation is the most common application method. Methods should be used to improve irrigation efficiency by minimizing evaporative water loss and reducing labor costs.

• Without access to irrigation technology to stabilize and optimize cotton production, many more millions of hectares of land would be required to maintain current levels of world production.


16. fejezet - REFERENCESAlam, M., Rogers, D.H. 2009. Irrigation Management for Alfalfa, MF2868. Kansas State University Agricultural Experiment Station and Cooperative Extension Service Publication. Manhattan, Kansas. Available from http://www.ksre.ksu.edu/bookstore/pubs/MF2868.pdf

Alfalfa managed root zone for irrigation. http://weru.ksu.edu

Alfalfa Production Handbook, C-683. 1998. Kansas State University Agricultural Experiment Station and Cooperative Extension Service Publication. Manhattan, Kansas. Available from http://www.ksre.ksu.edu/bookstore/pubs/C683.pdf

Allen, S., Nehl, D., Kochman, J., Salmond, G. 2012. 3.6 Irrigation and cotton disease interactions. In: WATERpak Guide for irrigation management in cotton, Section 3: Irrigation management of cotton. Available from: http://www.cottoncrc.org.au/industry/Publications/Water/WATERpak/WATERpak_S3_Irrigation_management_of_cotton

Ángyán J. – Menyhér Z.:1988. Integrált alkalmazkodó növénytermesztés. GATE – KSZE, Gödöllő - Szekszárd.

Ángyán J.: 1985. Nagyüzemi árukukorica-termesztés - A kukoricatermesztés területi elhelyezése. [In: Menyhért Z. (ed.) A kukoricatermesztés kézikönyve.] Mezőgazdasági Kiadó, Budapest, 199-228.

Benett, J. M. – Mutt, L. S. M. – Rao, P. S. C. – Jones, J. W.: 1988. Interactive effects of nitrogen and water stresser on biomass accumulation, nitrogen uptake, and seed yield of maize. Field Craps Research. 19. 4: 297-311.

Berenguer, P. – Santiveri, F. – Boixaderac, J. – Lloveras, J.: 2009. Nitrogen fertilisation of irrigated maize under Mediterranean conditions. European Journal of Agronomy. 30. 3: 163-171.

Berzsenyi Z.:1993. A N-műtrágyázás hatása a kukorica (Zea Mays L.) növekedésének és növekedési jellemzőinek dinamikája eltérő évjáratban. Növénytermelés. 42. 5: 457-471.

Bilbro, J.D. 2007. Deciding when to terminate cotton irrigation. Southwest Farm Press. Available from: http://southwestfarmpress.com/deciding-when-terminate-cotton-irrigation

Bocz E (szerk) 1992: Szántóföldi növénytermesztés. Mezőgazda Kiadó, Budapest.

Bouman, B.A.M., Lampayan, R.M., Tuong , T.P. 2007. Water management in irrigated rice: coping with water scarcity. Los Baños (Philippines): International Rice Research Institute. 54 p. Available from: http://books.irri.org/9789712202193_content.pdf

Brouwer-Heibloem,1986.: Irrigation Water Management: Irrigation Water Needs – FAOBurgonya termesztése. In: Radics, L. (ed) 1994. Szántóföldi növénytermesztéstan. Available from: http://mek.oszk.hu/01200/01216/01216.htm

Burgonya. In: Bocz, E. (ed) 1992. Szántóföldi növénytermesztés. Mezőgazda Kiadó, Budapest.

Carlson, L., Bauder, J., 2005. Sugarbeet Agronomy 101. Montana State University, Extension Water Quality Program, Irrigation Management. Available from: http://waterquality.montana.edu/docs/irrigation/sugarbeet101.shtml

Cotton Production Manual. Using Subsurface Drip Irrigation. Netafim, USA. Available from: http://www.netafimusa.com/files/literature/agriculture/other-literature/crop-applications/Cotton-Manual.pdf

Crop-specific Protocol Peas (picking, fresh). Redtractor Assurance for Farms. Fresh Produce Sheme. 2011. Available from: http://assurance.redtractor.org.uk/resources/000/594/883/Peas_picking_fresh_2011.pdf

Cukorrépa. In: Bocz, E. (ed) 1992. Szántóföldi növénytermesztés. Mezőgazda Kiadó, Budapest.


REFERENCES

Curwen, D. 1994. Water stress-related disorders. Nebr Potato Focus, Proc. pp. 22-28. UNL PHREC 94-04.

Dobos A. – Nagy J.:1998. Az évjárat és a műtrágyázás hatása a kukorica (Zea mays L.) szárazanyag-produkciójára. Növénytermelés. 47. 5: 513-524.

Doorenbos-Pruitt, 1977: FAO Irrigation and Drainage Paper: Guidelines for predicting crop water requirements – FAO

Efetha, A. 2011. Irrigation Scheduling for Pea in Southern Alberta. Agri-Facts. Practical Information for Alberta’s Agriculture Industry. Agdex 142/561-2. Available from: http://www1.agric.gov.ab.ca/$department/deptdocs.nsf/all/agdex13625

Efetha, E. 2011. Irrigation Scheduling for Potato in Southern Alberta. Agri-Facts. Agdex 258/561-1. Available from: http://www1.agric.gov.ab.ca/$department/deptdocs.nsf/all/agdex13571

Filep Gy., 1992.: Talajtan. Mezőgazda Kiadó, Budapest.

Formation of „milk layer” on maize kernel. Erick Larson’s picture, available from: http://msucares.com/crops/corn/images/milklinehalf.jpg

Fritz, V.A., Tong, C.B., Rosen, C.J., Wright, J.A. 2010. Sweet corn (vegetable crop management). University of Minnesota, Extension Publication. Available from: http://www.extension.umn.edu/distribution/cropsystems/dc7061.html

General information relating to climate and soil requirements of cotton crop. http://www.netafim.com/crop/cotton

Gibb, D., Neilsen, J., Constable, G. 2012. 3.1 Cotton growth responses to water stress. In: WATERpak Guide for irrigation management in cotton, Section 3: Irrigation management of cotton. Available from: http://www.cottoncrc.org.au/industry/Publications/Water/WATERpak/WATERpak_S3_Irrigation_management_of_cotton

Growing Irrigated Potatoes. North Dakota State University Extension Circular, AE-1040. 1999. Available from http://www.ag.ndsu.edu/pubs/plantsci/rowcrops/ae1040-2.htm

Hanson, B. R., Bali, K.M., Sanden, B.L. 2007. Irrigating alfalfa in arid regions. IN C. G. Summers and D. H. Putnam, eds., Irrigated alfalfa management in Mediterranean and Desert zones. Chapter 16. Oakland:, Agriculture and Natural Resources, University of California, 8293. Available from http://alfalfa.ucdavis.edu/IrrigatedAlfalfa

Harmati I.:1981. A kukoricaöntözés hatékonyságának növelési lehetőségei. Tudomány és Mezőgazdaság. 19. 4: 45-50.

Heatherly, L.G. 2005. Fine Tune Schedule for Corn Irrigation. Delta Farm Press, V. 62, No. 21, May 27, 2005. Available from: http://www.soydoc.com/images/WEBSITE_ARTICLE.pdf

Heiniger, R.W. 2000. Irrigation and Drought Management. Corn Guide. Chapter 4 . Available from: http://www.ces.ncsu.edu/plymouth/cropsci/cornguide/Chapter4.html

Huzsvai L. – Nagy J.:2003. A műtrágyázás hatása a kukorica (Zea mays L.) termésére öntözés nélküli és öntözéses termesztésben. Növénytermelés. 52. 5: 533-541.

Irmak, S., Hay DeLynn, R., Anderson, B.E., Kranz, W. L., Yonts, C.D. 2007. Irrigation Management and Crop Characteristics of Alfalfa, G1778. University of Nebraska–Lincoln Extension Publication. Available from http://ianrpubs.unl.edu/epublic/live/g1778/build/g1778.pdf

Irrigation Best Practice Water Management for Potatoes. Department for Environment , Food and Rural Affairs (DEFRA). 2005. A Guide for Growers. Available from http://79.170.40.182/iukdirectory.com/iuk/pdfs/water%20management%20for%20potatoes.pdf

Irrigation Management. Potato Growth and Irrigation Scheduling. CropWatch: Potato Education Guide, University of Nebraska–Lincoln. 2013. Available from http://cropwatch.unl.edu/web/potato/plant_growth


REFERENCES

Izsáki, Z. 2004. Szántóföldi növények vetőmagtermesztése és kereskedelme. Mezőgazda Kiadó, Budapest.

King, B.A., Stark, J.C. 1996. Potato Irrigation Management, BUL0789. University of Idaho Cooperative Extension System Publication. Available from: http://www.cals.uidaho.edu/edcomm/pdf/BUL/BUL0789.pdf

Kizer, M. Soybean Irrigation. In: Soybean Production Guide 2009, E-967. Oklahoma Cooperative Extension Service, Division of Agricultural Sciences and Natural Resources, Oklahoma State University. p. 33-41. Available from: http://oilseeds.okstate.edu/production-information/soybean/E967SoybeanGuide2009.pdf

Kovács Gábor (ed.), 1968: Az öntözés kézikönyve. Mezőgazdasági kiadó, Budapest

Kranz, B., Benham, B. 2004. Does Irrigation Improve Soybean Yields? p. 8-17. Proceedings of the 16th Annual Central Plains Irrigation Conference & Exposition. Available from: http://www.ksre.ksu.edu/irrigate/OOW/P01/KranzBenham_IrrigSoybeanYeild.pdf

Kranz, W.L., Irmak, S., van Donk, S.J., Yonts, C.D., Martin, D.L. 2008. Irrigation Management for Corn, G1850. University of Nebraska–Lincoln Extension, Institute of Agriculture and Natural Resources Publication, NebGuide. Available from: http://www.ianrpubs.unl.edu/live/g1850/build/g1850.pdf

Kruppa, J. 2007. A környezeti tényezők hatása a burgonya termésére és minőségére. Agroinform. 2007/7. Available from: http://www.agroinform.com/aktualis/Agroinform-szaklap-A-kornyezeti-tenyezok-hatasa-a-burgonya-termesere-minosegere/20070709-2721/

Kukorica. In: Bocz, E. (ed) 1992. Szántóföldi növénytermesztés. Mezőgazda Kiadó, Budapest.

Láng I. – Csete L. – Harnos Zs.: 1983. A magyar mezőgazdaság agroökológiai potenciálja az ezredfordulón. Mezőgazdasági Kiadó, Budapest.

Ligetvári F., 2008: Öntözés. Szent István Egyetem, Gödöllő

Lucerna. In: Bocz, E. (ed) 1992. Szántóföldi növénytermesztés. Mezőgazda Kiadó, Budapest.

Melvin, S.R., Payero, J.O., Klocke, N.L., Schneekloth, J.P. 2005. Irrigation Management Strategies for Corn to Conserve Water. p. 76-83. Proceedings of the 17th Annual Central Plains Irrigation Conference & Exposition. Available from: http://www.ksre.ksu.edu/irrigate/OOW/P05/Melvin.pdf

Nagy J., 2002: Kukoricatermesztés. Akadémiai Kiadó, Budapest.

Nyíri László (ed.), 1997: Az aszálykárok mérséklése. Mezőgazda Kiadó, Budapest.

Orloff, S., Hanson, B., Putnam, D. 2003. Utilizing Soil-Moisture Monitoring to Improve Alfalfa and Pasture Irrigation Management. Available from http://www.plantmanagementnetwork.org/pub/cm/management/2003/moisture/

Pavlista, A.D. 1995. Potato production stages: Scheduling key practices. UNL Coop Ext Circ 1249.

Pendergast, L. Crop water use. Chapter 10. 2010. In: Australian Cotton Production Manual. p. 58-61. Available from: http://www.cottoncrc.org.au/industry/Tools/Cotton_Seasonal_Prompter/Continual_Topics/Water_Management

Perry, C., Barnes, E. (eds) 2012. Cotton Irrigation Management for Humid Regions. Cotton Incorporated. Available from: http://www.cottoninc.com/fiber/AgriculturalDisciplines/Engineering/Irrigation-Management/cotton-irrigation-web.pdf

Pethő Menyhért, 1993: Mezőgazdasági növények élettana. Akadémiai Kiadó, Budapest

Racskó, J. 2003. A cukorrépa öntözése. Agrárágazat. 2003. szeptember http://www.pointernet.pds.hu/ujsagok/agraragazat/2003-ev/09-szeptember/agrarag-11.html

Racskó, J. 2004. A burgonya öntözése. Mezőhír. VIII. 2004-04. Available from: http://mezohir.hu/mezohir/2004/04/a-burgonya-ontozese

Racskó, J. 2005. Szántóföldi kultúrák öntözése. A kukorica öntözése. Mezőhír. 2005. április.


REFERENCES

http://mezohir.hu/mezohir/2005/04/szantofoldi-kulturak-ontozese/

Racskó, J., Budai L. 2005. A burgonya vízellátása, az öntözés hatása a gumók minőségére. Agrárágazat. 2005. május. Available from: http://www.pointernet.pds.hu/ujsagok/agraragazat/2005/05/20090103184450871000000478.html

Rhoads, F.M., Yonts, C.D., 2000. Irrigation Scheduling for Corn—Why and How. In: Corn National Handbook, Water Management (Irrigation), NCH-20. University Extension Publication, Iowa State University. Available from: http://corn.agronomy.wisc.edu/Management/pdfs/NCH20.pdf

Rizs. In: Bocz, E. (ed) 1992. Szántóföldi növénytermesztés. Mezőgazda Kiadó, Budapest.

Rogers, D.H. 2007. Chapter Irrigation. In: Corn Production Handbook, C-560. Agricultural Experiment Station and Cooperative Extension Service Publication, Kansas State University. p. 30-36. Available from: http://www.atchison.ksu.edu/doc39482.ashx

Ruzsányi, L. 2003. A cukorrépa öntözése. Beta-füzetek. 9. szám. http://www.beta-kutato.hu/ontozeshu.htm

Sadras-Grassini-Steduto, 2007: Status of water use efficiency of main crops SOLAW Background Thematic Report – FAO

Slaton, N.A. (ed) 2006. Rice Production Handbook, MP192, Chapter 9. University of Arkansas, Division of Agriculture, Cooperative Extension Service Publications. p. 75-86. Available from: http://www.uaex.edu/Other_Areas/publications/PDF/MP192/chapter9.pdf

Soybeans - Crop Irrigation, Soil and Water Management. 2006. Division of Agriculture, Cooperative Extension Service, University of Arkansas. Available from: http://www.aragriculture.org/soil_water/irrigation/crop/soybeans.htm

Stefanovits Pál 1975: Talajtan. Mezőgazdasági Kiadó, Budapest.

Sustainable Rice Best Management Practices BMPs, Pub. 2805, 2011. Louisiana State University Agricultural Center, Louisiana Agricultural Experiment Station and Louisiana Cooperative Extension Service Publication. Available from: http://www.lsuagcenter.com/NR/rdonlyres/1DDC5753-C653-42B0-BE09-34BA4062283A/83751/pub2805RiceBMPLOWRES.pdf

Sweet Corn Information Kit. Queensland Government. 2005. Available from: http://era.deedi.qld.gov.au/1980/7/sweetcorn7.pdf

Sweet corn. Drought Advisory Publication, EM4815. 2001. Washington State University, Cooperative Extension. Available from: http://cru.cahe.wsu.edu/CEPublications/em4815/em4815.pdf

Sweet corn. Ohio Vegetable Production Guide. 2010. Available from: http://ohioline.osu.edu/b672/pdf/Corn.pdf

Szabó I. (2003): Vetésforgó és öntözés. Szaktudás Kiadó Ház Rt., Budapset.

Szalóki, S. 1988. Az öntözéses gazdálkodás újabb kutatási eredményei. Tudományok. ÖKI, Szarvas.

Szász Gábor, 1988: Agrometeorológia. Mezőgazdasági Kiadó, Budapest

Szász-Tőkei ed., 1997: Meteorológia mezőgazdáknak, kertészeknek, erdészeknek – Mezőgazda

Széles, A.: 2008. Evaluating the correlation between SPAD values and the yield of maize (Zea Mays L.) on different nutritive and water supply levels. (doctoral – PhD - dissertation), University of Debrecen, Centre of Agricultural Sciences Engineering, Debrecen p. 110

Szója. In: Bocz, E. (ed) 1992. Szántóföldi növénytermesztés. Mezőgazda Kiadó, Budapest.

Thomas, J.G., Blaine, A. 2006. Soybean Irrigation. Publication 2185. Extension Service of Mississippi State University. Available from: http://msucares.com/pubs/publications/p2185.htm

Tóth, 2006: A XXI. Század öntözőrendszerei – Visionmaster


REFERENCES

van Loon, C.D. 1981. The effect of water stress on potato growth, development, and yield. Am Potato J 58:51-70.

Vermes L. (ed.) 1997: Vízgazdálkodás. Mezőgazda Kiadó, Budapest.

Whitaker, J. Irrigation. In: 2012 Georgia Soybean Production Guide. College of Agricultural & Environmental Sciences and the U. S. Department of Agriculture cooperating, University of Georgia. p. 77-79. Available from: http://www.caes.uga.edu/commodities/fieldcrops/soybeans/documents/2012SoybeanProductionGuideFINAL.pdf

Yonts, C.D., Palm, L.K., 2008. Sugarbeet Production Guide, Chapter 12 Irrigation Management, EC156. University of Nebraska–Lincoln Extension, Institute of Agriculture and Natural Resources Publication. Available from http://www.ianrpubs.unl.edu/epublic/live/ec156/build/ec156-12.pdf

Zöldborsó. In: Bocz, E. (ed) 1992. Szántóföldi növénytermesztés. Mezőgazda Kiadó, Budapest.


regi.tankonyvtar.hu€¦ · web viewsaturated soil culture 0 9.2. system of rice intensification 0...

Documents