Agricultural Water Management, 13 (1988) 83-91 83 Elsevier Science Publishers B.V., Amsterdam -- Printed in The Netherlands

An Economic Evaluation of Sugar Cane Production under Different Water Supply Systems in Thailand

W.J. BRZESOWSKY and A.E.M. VAN VILSTEREN

Euroconsult, P.O. Box 441, 6800 AK Arnhem (The Netherlands)

(Accepted 28 March 1987)

ABSTRACT

Brzesowsky, W.J. and Van Viisteren, A.E.M., 1988. An economic evaluation of sugar cane pro- duction under different water supply systems in Thailand. Agric. Water Manage., 13: 83-91.

In a vegetative crop like sugar cane, soil water stress will invariably result in reduced growth and yield. Under inadequate rainfall conditions such a crop needs supplemental irrigation to max- imize the yield.

The present article discusses the relationship between sugar cane yield and rainfall/irrigation requirements. Special attention is given to the potential sugar cane yields and benefit/cost ratios in the Malaiman area in Thailand, under four water conveyance systems (from low- to high- density irrigation and drainage network) and under optimized rainfed cultivation.

A linear relationship between cane yield and water use is applied for the prediction of potential crop yields for the various water conveyance systems. These yields are compared with the actual cane production in pilot areas with different irrigation infrastructure, which has been monitored over a period of years. Actual yields fall short of predicted in all cases. This is mainly be attributed to the low cane prices, resulting insub-optimal cultivation practices by the farmers.

Prediction of potential sugar cane yields for local circumstances is quite possible. At present sugar cane price levels, development of a low-density irrigation infrastructure seems to be the most economical solution.

INTRODUCTION

Sugar cane is grown under rainfed conditions as the main upland crop in the Malaiman area, which is part of the Greater Mae Klong River Basin in the west of Thailand. Because rainfall is marginal and erratic, yields are low and vary from year to year.

In areas with irregular rainfall distribution yields are lower for rain-depen- dent than for irrigated crops, even if the total annual rainfall is sufficient. An explanation for this is that a plant subjected to intermittent or prolonged pe- riods of soil water stress cannot make immediate and efficient use of a renewed supply of water (Irvine, 1983; Venkataramana et al., 1984).

0378-3774/88/$03.50 © 1988 Elsevier Science Publishers B.V.

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The growth rate of vegetative organs is more sensitive to water shortage than that of reproductive organs. Similarly, fresh weight has been found to be more affected by water shortage than is dry weight { Thompson, 1976).

In tropical lowlands, erratic marginal rainfall will often result in low cane yields and low sugar-on-cane values. The introduction of an appropriate irri- gation and drainage infrastructure to counteract the effects of marginal and erratic rainfall will result in increased sugar cane yields. In addition, these measures will reduce the production costs by allowing prolonged crop cycles.

In 1980, various alternatives for irrigation and drainage infrastructure were studied for the upland soils of Malaiman (RID/Ilaco-Empire, 1980, 1985). Of the total area of 175 000 ha, some 40% was considered suitable for (irrigated) upland cropping. Due to limited experience with development of irrigation for upland crops in Thailand, and hence the rather limited data regarding costs, benefits, farmers' response etc., it was recommended that a pilot project be started for studying different water conveyance methods and their effects on sugar-cane cultivation and yields. Four options were considered for supplying the required amount of supplement irrigation: (a) Intensive On-Farm Development { OFD ) : all farmers will have direct ac-

cess to irrigation water; full-scale land consolidation, including land levelling.

(b) Semi-intensive OFD: as (a), but irrigation and drainage ditches will follow the present plot boundaries; no land levelling.

( c ) Extensive OFD: as (b), but only 70% of the farmers will have direct access to irrigation water.

(d) No OFD: only a main and secondary irrigation and drainage system will be constructed.

The irrigation in the pilot areas started in 1983 and now after 3 years suffi- cient field data have been obtained to make an economic evaluation.

CLIMATE AND SOILS

The study area has a wet season from May to November with the lowest rainfall in June and July, and a dry season from November to May. The aver- age annual rainfall is about 1000 mm, varying from 850 to 1100 mm depending on the location. The lowest figures are recorded for Phanom Thuan in the west, the highest for Kamphaeng Saen in the south. Of the total annual rainfall, 85% occurs in the wet season. A review of evapotranspiration and rainfall data is given in Table 1.

Daily ET o values vary between 4.5 and to 7 mm/day, with an annual average of 5.5 ram/day. The highest daily values are recorded in March/April, i.e. at the end of the dry season; the lowest daily values occur from September to January.

TABLE 1

Relationship between monthly reference evapotranspiration (ETo) and precipitation (P)

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Month U-Thong Kamphaeng Saen

ETo P (P/ET0) ET0 P (ram) (mm) X 100% (mm) (mm)

(P/ETo) × 100%

January 148 5 3 137 4 3 February 170 17 10 161 10 6 March 223 18 8 207 15 7 April 232 64 28 208 51 25 May 209 124 59 183 120 66 June 177 75 42 151 122 81 July 177 96 54 156 121 78 August 168 97 58 143 134 94 September 142 233 164 134 249 186 October 143 166 116 141 206 146 November 143 23 16 134 51 38 December 143 11 8 136 5 4

The Malaiman upland soils are fairly uniform: they belong to the same tax- onomic group (Udic Haplustalfs) and comprise virtually one main soil map- ping unit (Kamphaeng Saen soil series). They are intruded in the west by (diluvial) Roi Et and Korat soil series and by recent alluvial deposits of the Mae Klong river, and bounded in the east by recent (marine) alluvial deposits of the Song Phi Nong and Nakhorn Chaisi rivers.

The Roi Et /Kora t soil complexes, of relatively minor importance on the uplands, are only used for sugar cane growing if they are not subject to seasonal floods. In the last decade, sugar cane cultivation has also slightly expanded towards the recent alluvial clay soils situated above flood level.

Physiographically, the Malaiman uplands are part of a former terrace of the Mae Klong river, a fan-shaped area sloping gently from west to east. The area is intersected by many old river branches which run in an easterly or northerly direction and contribute to surface drainage. Because of the presence of levees and depressions relief is complex, which may necessitate pumping and sprin- kler irrigation in some places.

The non-calcic Kamphaeng Saen soil series are generally well-structured, deep soils. They are brown, medium-textured in the surface horizons, and well drained. Towards the deeper layers, i.e. below the active rooting zone, the finer- textured subsoils gradually become coarser. In spite of a lower permeability of the B-horizon, the internal drainage of the Kamphaeng Sean soil series is good. If they are left uncultivated, however, the surface is liable to slaking because of its high silt content. The surface horizons are slightly acidic, the subsoil

86

horizons show a neutral reaction. Water retention capacity is fair to good, rang- ing from 10 to 15 cm over a depth of 120 cm.

Because of their favourable morphological properties and satisfactory in- herent fertility, the soils are considered highly productive and suitable for a great number of annual and perennial upland crops. Under a system of sup- plementary irrigation and double cropping they are likely to need routine ( maintenance ) fertilizer dressings ( notably nitrogen and phosphate).

The rainfed growing season is determined by soil water availability. The beginning of the growing or planting season is in May. Due to the amount of rainfall in September and October and physical properties of the main soils in the area, maturation is reached in November and December, when evapotran- spiration rates are low. The total growing season is thus about 6-8 months, which is long enough for annual crops, but marginal for sugar cane, with op- timal crop ages varying from 12 to 14 months.

Two other reasons for low sugar cane yields are that the distribution of rain- fall during crop establishment and during stages with full canopy is too uneven to permit regular crop emergence and vegetative development, and that the efficiency of the higher rainfall occurring from July till October is reduced by the fact that cane planted in the period May-June will enter the second half of the rainy season as a partially canopied crop only.

IRRIGATION REQUIREMENTS

Lack of water has a great impact on plant development, in particular because of the resulting reduction in photosynthesis and leaf area index ( Irvine, 1983; Snyder and Carlson, 1984). Water shortage during the active growing period of sugar cane will reduce stalk length, while inadequate water supply in the period prior to closing-in may induce tiUering. Contrary to what could be ex- pected, water shortage during the active stage of growth hardly ever leads to increased sugar content. It is reasonable to expect a direct relationship be- tween consumptive use of water and biological or economic yield, particularly in the case of a vegetative crop like sugar cane (Thompson, 1976, 1978; Yates, 1978; Shih, 1985).

The optimal gross annual rainfall requirements for sugar cane grown in hot and humid tropical areas range from 1500 to 2000 mm. In studies conducted in African countries (Bassereau, 1979 ) the water requirements were estimated at 15-18 mm per t of cane per ha. An annual crop yielding, for example, 100 t per ha would require 1500-1800 mm. In Malaiman, with its average rainfall of 1000 mm per year, the potential annual rainfed yield would vary between 55 and 65 t per ha, which is considerably higher than the yields obtained at pres-

t, metric tonne = 1000 kg.

87

ent (30-40 t per ha) . This is probably caused by the suboptimal rainfall distribution.

In the Malaiman area, supplemental irrigation of about 1000 mm net during critical development stages could, therefore, lead to a substantial increase in yields. Moreover, research has shown that early planting, made possible by the availability of irrigation water, and reduced furrow spacing will also lead to higher yields (Irvine, 1983; Brzesowsky, 1985/1986).

YIELDS

The potential cane growers' yields to be obtained under irrigated conditions can be estimated with the following formula (Thompson, 1977 ):

Y = ST Y ( E T ---- 100 mm) X 0.7

where Y is the cane yield expected ( t /ha) , and Y ( ET ---- 100 ram) the potential yield ( t /ha) per 100 mm ET reached under experimental conditions; the factor 0.7 represents the average growers' performance of 70%. Potential yields can attain a level of at least 9-10 t or more per ha per month of age. Under optimal conditions of water supply ( hence ET a ----- ETm) and soil and crop management, 1 t of cane per ha can be synthesized by the cane crop per 10 mm of actual evapotranspiration.

It defects occur in any of the crop-growing factors, crop productivity is low- ered, for instance when ETa < ETm. The relationship between relative yield de- crease and relative evapotranspiration deficit has been expressed by Doorenbos and Kassam (1978) as:

1-- Y" = Ky(1 - E T ' ) Ym ETm

where Ky is the yield response factor, Ya and Ym actual and maximum yield, and ETa and ETra actual and maximum evapotranspiration.

Projections of average annual yields for the various water conveyance sys- tems under consideration are given in Table 2. For the conditions in Malaiman, these projections are considered rather conservative, the more since possible deficiencies in chemical soil fertility may be easily offset by the application of fertilizer and soil amelioration residues such as filter-press mud and molasses.

Since 1983 agro-economic surveys were carried out in a pilot area with semi- intensive OFD ( option b ), in an area where farmers pump water from the main system ( option d ) or from tubewells, and in a third area where rainfed cane is grown. The actual average yields obtained in the study years are also presented in Table 2. It is clear that the yields farmers attained were below those estimated. The main reasons for this are, in order of importance: low cane prices (1985; US$ 14 pert); application of inappropriate agricultural practices, such as insufficient in-field levelling, planting too late, use of low-

88

TABLE 2

Yields in the areas with the various water conveyance systems

Development option Yield reduction coefficient a

Average annual yield (t/ha)

Projections

Potential Actual b

Realized in pilot areas c

Intesive OFD 1.0 125 100 - Semi-intensive OFD 0.9 115 90 66 Extensive OFD 0.8 100 80 - Main system only 0.7-0.75 90 65 53 No development 0.5-0.55 65 45 31 (rainfed)

Source: RID/Ilaco-Empire, 1980 aIncludes the effects on yield of water availability, infrastructural provisions, supporting services, crop management etc. bRefers to farmers' yields (70% of potential yields). CAverage figures of first 3 years (1983-1985).

grade seed cane, insufficient fertilization, etc.; slow adaptation to the new sit- uation due to the long cane cycle, low prices, and inadequate research and extension facilities in the area.

It may, however, be expected tha t the farmers potential yields will be real- ized, especially if sugar cane prices increase and if farmers adapt their culti- vation practices to the new situation.

ECONOMIC EVALUATION

The investment costs for design and construction of the various water-con- veyance systems a, b, c and d are US$1600, 1350, 1200 and 660 per ha, respec- tively; the life-spans of OFD works and main system are estimated at 20 and 50 years. With an interest rate of 10%, the annual depreciation cost would be as presented in Table 3. The cost of operation and maintenance of the main irrigation and drainage system is about 2 % of the investment cost and is borne by the Royal Irrigation Department of Thailand. The maintenance cost of the tertiary conveyance system has to be borne by the farmers and is currently US$14 per ha for the semi-intensive and the intensive OFD system. For the extensive system it is estimated at US$10 per ha.

The economic value of the irrigation water is, for the time being, zero because more water is available than can be used for irrigation or other applications.

The added value of the cane produced under the various development op- tions, as presented in Table 4, is defined here as the additional average farm

89

TABLE 3

Annual depreciation and maintenance cost of the different water conveyance options (US$/ha)

Depreciation Maintenance Total

Main OFD Main OFD System System

Intensive OFD 66 Semi-intensive OFD 66 Extensive OFD 66 Main system 66

112 13 14 205 82 13 14 175 65 13 10 154

- 1 3 - 79

Capital recovery factors: OFD: i = 10%; n = 20 years: 0.1175. Main system: i = 10%; n = 50 years: 0.1009.

income compared with rainfed cultivation. The data are based on real yield data given in Table 2.

The benefit-cost ratio as presented in Table 5 indicates that even at the present yield levels the benefit-cost ratio is acceptable. The highest value is reached when only the main system is constructed, even if potential yield levels are realized. It should be noted, however, that in the main system development option the farmers have to pump the water from the main system onto their fields and thus consume fossil fuel, which has to be imported. Hence, from a macro-economic point of view, this may not be the favoured solution, consid- ering that in the other options the water is delivered to the fields by gravity.

A sensitivity analysis regarding the cane price level showed that with a 25% higher cane price (US$17/t) the conclusion remains the same for the actual yield levels. If, however, potential yields are realized then the intensive OFD option shows the highest B/C ratio (B/C = 2.9) (Fig. 1 ).

At present sugar-cane price levels, the development of only a main irrigation and drainage system seems the most economical solution. However, if macro- economic criteria are applied, introduction of an On-Farm Development (OFD) system could be more economical. If that is the case, intensive or semi-inten-

~18

c4,

16

14

I I I ~ l l I I I I

1.6 2.0 214 2.8 3.2

Fig. 1. Benefit-cost ratios for dLfferent water conveyance systems at dLfferent cane price levels: I, intensive OFD, potential yield; 2, semi-intensive OFD, potential yield; 2a, semi-in~nsive OFD, actual yield; 3, extensive OFD, potential yield; 4, main system only, potential yield; 4a, main system only, actual yield.

90

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a~

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a~

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c~

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TABLE 6

Benefits added values and costs of the different water conveyance options (US$/ha)

9 1

Benefits (Table 4) Costs B/C (Table 3)

Actual Potential Actual Potential yields yields yields yields

Intensive OFD - 420 205 - 2.0 Semi-intensive OFD 260 330 175 1.5 1.9 Extensive OFD - 240 154 - 1.6 Main system only 203 160 79 2.6 2.0

sive OFD may prove to be the most economical solution provided the potential yields can be achieved.

ACKNOWLEDGEMENTS

The authors wish to thank the Management of Euroconsult for their per- mission to publish this material, and Mr. J.J. Bak for his editorial assistance.

REFERENCES

Bassereau, M., 1979. Sugarcane mechanized irrigation; technical possibilities and economic lim- its. Aft. Agric. (France), 43: 20-21, 23.

Brzesowsky, W.J., 1985/1986. Factors influencing sugar-cane production and quality; a review. Agric. Int., 37: 256-278; 38: 30-35.

Doorenbos, J. and Kassam, A.H., 1978. Yield response to water (synopsis). FAO, Rome. Irvine, J.E., 1983. Sugar-cane. In: Syrup. Potential Productivity of Field Crops under Different

Environments. International Rice Research Institute, Los Bafios, The Philippines. RID/Ihco-Empire, 1980. Greater Mae Klong Malaiman Irrigation Project. Feasibility study. Royal

Irrigation Department, Bangkok, Thailand. RID/Ilaco-Empire, 1984/1985. Mae Klong Irrigation Project Malalrn~r~, Phase I. Monitoring and

evaluation report series. Sugar-cane monitoring report Nos. 3 and 4. Royal Irrigation Depart- ment, Bangkok, Thailand.

RID/Ilaco-Empire, 1985. Mae Klong Irrigation Project Malaiman, Phase I. Review of the distri- bution system and on-farm lay-outs in the sugar-cane areas of Malaiman. Royal Irrigation Department, Bangkok, Thailand.

Shih, S.F., 1985. Use of sugar-cane yield and evapotranspiration relationships to improve water management. Sugar-cane, 1: 3-7.

Snyder, F.W. and Carlson, G.E., 1984. Selecting for partitioning of photosynthetic products in crops. Adv. Agron., 37: 47-73.

Thompson, G.D., 1976. Water use by sugar-cane, I and II. S. AfT. Sugar. J., 60: 593-601; 60: 627-636. Thompson, G.D., 1977. Irrigation of sugar-cane, I and II. S. AfT. Sugar J., 61: 126-132; 61:161-175. Thompson, G.D., 1978. The production of biomass by sugar-cane. Proc. S. Afr. Sugar Technol.

Assoc., 52: 1-9. Venkata~_mA~_a, S. et al., 1984. Growth behaviour of field grown sugar-cane varieties in relation

to environmental parameters and soil moisture stress. Agric. For. Meteorol. Neth., 31:251-260. Yates, R.A., 1978. The environment for sugar-cane. World Soil Resour. Pep. FAO, 29: 58-72.