government of the philippines department of … technical notes on swc.pdf4.5 the principles behind...

TECHNICAL NOTES on

SOIL and WATER CONSERVATION by: Alex FJ Hamming

Ben Hur R Viloria Upland Development Programme Technical Assistance Team PO Box 81333, Davao, Philippines December 2000

GOVERNMENT of the PHILIPPINES

DEPARTMENT of AGRICULTURE

EUROPEAN COMMISSION

UPLAND DEVELOPMENT PROGRAMME in SOUTHERN MINDANAO (ALA-97/68)

SUSTAINABLE AGRICULTURE GROUP

Technical Notes on Soil and Water Conservation December 2000

i

TABLE of CONTENTS Page 1 BACKGROUND 1 2 APPROACH, CONCEPT and METHODOLOGY 2 2.1 Approach and Concept 2 2.2 Methodology 3 3 HOW TO RECOGNIZE EROSION 5 3.1 Symptoms of Erosion 5 3.1.1 Pedestal 5 3.1.2 Stones on the Surface 5 3.1.3 Exposed Root System 6 3.1.4 Layers of Soil 6 3.1.5 Rills 6 3.1.6 Gullies 7 3.1.7 Sedimentation in Rivers 8 3.1.8 Landslides 8 3.1.9 Muddy Colored Water 9 3.1.10 Comparing Fields 9 3.1.11 Crop Performance 10 3.2 Symptoms of Degeneration of the Environment 10 4 THE EROSION PROCESS 12 4.1 Splash-erosion 12 4.2 Stream Erosion (rill, gully) 13 4.3 Combination of Splash- and Stream Erosion 15 4.4. Showing the Erosion Process 15 4.5 The Principles behind Erosion Control Measures 16 5 AGRONOMIC METHODS 17 5.1 Land Preparation 18 5.2 Contour and Strip Farming 19 5.2.1 Contour Farming 19 5.2.2 Strip Farming 22 5.3 Cover Crops and Mulching 23 5.3.1 Cover Crops 23 5.3.2 Mulching 27 5.4 Cropping Systems 30 5.4.1 Crop Rotation 30 5.4.2 Relay Planting 30 5.4.3 Planting along Contours and Hedgerows 31 5.4.4 Bush Fallow 31 5.4.5 Multi-storey/Fruit Tree Integration 32 5.4.6 Integration of Pasture Cover Crops and Grasses 32

underneath Permanent crops/trees 5.4.7 Gradual Integration of Fruit trees/establishment 32

of Orchard alongside Annual Crops


ii

5.5 Crops and AEZ 35 5.5.1 Altitude and Slope 35 5.5.2 Rainfall 35 6 TECHNICAL METHODS 39 6.1 Introduction 39 6.2 Different Levels of Measures 39 6.3 Measures to reduce Run-off 40 6.3.1 Pole barriers 40 6.3.2 Terraces 41 6.3.3 Run-off control in gullies 43 6.3.4 Slope and embankment protection 45 7 WATER CONSERVATION 46 7.1 Introduction 46 7.2 Fishpond, an Integrated Model 46 7.3 Design and Construction of a Fishpond 49 7.3.1 Site Selection 49 7.3.2 Soil Structure and pH 50 7.3.3 Water Sources 51 7.3.4 Pond Embankments 53 7.3.5 Pond Size 54 7.3.6 Inlets and Outlets 54 8 STRATEGIC ACTION POINTS 56 REFERENCES 59 APPENDICES Appendix A Construction and Use of A-Frame for 60 Setting Contour Lines Appendix B Establishing a Vetiver Grass Nursery 64 Appendix C Rainfall 67 LIST of TABLES Table A Recommended Leguminous Cover Crops 25 Table B Recommended Crop Assortments 33 Table C Recommended Crops for the Uplands and Hilly Lands 36 Table D Recommended Crops for the High Lands 37 Table E Summary of Dry Months 38 Table F Dimensions Terrace 43


1

1 BACKGROUND Southern Mindanao is a high-rainfall, mountainous region recently denuded of rainforest cover due mostly to logging. The combination of high rainfall, moderate to steep slopes and the absence of an adequate vegetation cover exposes the area to an extreme erosion risk. The risk is further enhanced by the employment of destructive farming practices such as improper land use and cultivation practices (e.g. plowing, harrowing and furrowing along the slope), slash-and-burn agriculture and indiscriminate cutting of trees for firewood. Soil erosion and land slippage on steep slopes are evident in areas where shifting cultivation is practiced. Reports on declining soil fertility and the need to increase the use of fertilizers were heard from farmers in rural upland communities Many farmers that have settled in the upland watersheds have initiated a vicious cycle of exploitation, expanding their cultivated area rapidly meanwhile applying non-sustainable agricultural methods. In the long run, soil erosion is not only caused by poverty, it also breeds poverty [1]. The Upland Development Programme is a special project of the Department of Agriculture (Philippines) assisted by the European Community. It aims at improving the living standard of the rural population in five provinces in Southern Mindanao. A watershed management approach is applied to develop and test a sustainable and replicable agriculture model. The programme is a follow up of the Southern Mindanao Agricultural Programme (SMAP, 1992-1996) and has taken into account lessons learnt from the latter. UDP will operate in approximately 480 small watersheds covering an area of roughly 17,000 hectares. Among the proposed activities is the introduction to farmers of appropriate sound soil and water conservation measures. This report comprises technical notes on soil and water conservation and forms the base for training of trainers i.e. the municipal extension staff who will be engaged in working with farmers.


2

2 APPROACH, CONCEPT and METHODOLOGY 2.1 Approach and Concept From SMAP it was learnt that the farmers’ adoption of proposed soil conservation measures was not really that widespread. The soil conservation methods were largely based on the technical sound SALT technology, developed by MBLRC [4, 7]. Among other reasons (non-ownership of land, less attention to social preparations), the main reasons for the low adoption was that farmers complained about the laborious maintenance and lack of seeds and seedlings. Moreover, there was reluctance to plant non-cash crop yielding plants. Farmers see agriculture primarily as a food provider and money earner. In this set up, the proposed conservation methods are mixtures of simple and cost effective, short-term mitigating and long-term sustainable interventions largely related to arable farming. Other interventions aim on reducing run-off (overland flow) without a direct link to crop production. Water conservation is best served by implementing proposed long-term soil conservation methods which strongly emphasize the cultivation of fruit and commercial crops. Most tree crops have well developed roots that stabilize topsoil and enhance the soil’s water holding capacity. A more direct approach on water conservation is the fishpond concept that aims on intercepting run-off and trapping water for profitable use. Unlike SMAP this Programme will put a lot of energy in strengthening community institutions. This will increase the organizational capacities of a community making the proposed interventions more likely to be adopted. One of the biggest challenges the Programme will face is how to deal with the cultivation of seasonal crops, in general, and corn cultivation, in particular, on moderate to steep slopes. The latter is quite common in the Programme area. Corn production is a traditional practice, aiming on food security, yet not recommended as it makes the topsoil prone to erosion. Here mitigating measures are proposed like the establishment of rapid spreading leguminous cover crops, minimum tillage, mulching, contour cultivation with strips and hedge rows. The measures are effective on the short term and should be seen as a way of damage control on the excess of current upland farming practices. On the long run the Programme aims on more sustainable interventions such as the establishment of vegetative barriers (strips, hedgerows). A number of cropping systems are discussed that can fit in appropriate soil conservation methods. A lot of attention goes to the cultivation of fruit and commercial trees integrated with seasonal and cover crops or pastures. Farmers commonly lack the sources to purchase seedlings and other inputs. Moreover, good quality planting materials may also not be available everywhere. As the project was never designed to provide any financial aide to set up and manage nurseries, farmers may have to establish small, self-sustainable nurseries themselves either individually or at the Sitio/Barangay level. LGU extension staff will fulfill an important role here in promoting this concept and in training interested farmers on the technical and economical aspects. During the SMAP implementations, most seedlings were provided to farmer beneficiaries at almost no expense. The challenge is now to change the


3

perception that planting materials are no longer given free. In the absence of cash the newly set up credit facilities may play an important role here. To mitigate the detrimental effects of a dry spell on agriculture (water stress for seedlings and young trees) fishponds are proposed in the vicinity of perennial flows (springs, streams) to trap some water. The pond will generate food and cash (that may be utilized for the purchase of seeds/seedlings) and provides water to irrigate vegetable gardens and young orchards. Each proposed soil and water conservation measure might have its side effects in terms of social, financial or economic constraints. The type of measures to be adopted may vary site, municipality or from province, depending on the specific interests of individual farmers. The emphasis will lie on the acceptance by farmers. The LGU extension staff will assess which type of soil/water conservation method farmers would be more responsive to and will likely adopt. In pace with the development of the small scale nurseries, extension on soil/water conservation will gradually shift from short term to long term interventions with emphasis on the cultivation of fruit and commercial crops. Among others, slope and altitude are two important factors for crop cultivation as they are linked with the crop’s specific physiological features. Steep slopes restrict the growth of shallow rooting crops whereas the temperature decreases with higher elevations. Following the draft Agro-Ecological Zoning (AEZ) recommended crops are linked to the slope-altitude classes. Info on slope and altitude for each sitio can be derived from the Sitio specific AEZ map. Cross checkings can be made in the field using the altitude watch and clinometer. Recommendations on other crop requirements such as rainfall, plant spacing and maintenance are presented as well. The rainfall distribution for each province is provided. A summary of the concept: 1. Soil and water conservation is integrated in cultivation farming as much as

possible to enhance adoption; 2. Short term interventions focus on simple and cost effective measures which

quickly pay off at little costs (land cultivation, mulching, regenerating ground covers);

3. Long term interventions focus on establishment of fruit and fast growing wood trees, intercropped with perennials and/or seasonal crops; Establishment of sustainable small scale nurseries is a prerequisite;

4. Compromise between soundness technical measures and acceptance measures by farmers;

5. Soil conservation interventions are linked to AEZ parameters, specifically slope and altitude.

2.2 Methodology In preparing the technical notes, an effort was made to keep the message simple. The notes outline the basic problems of soil erosion with the advantages of each soil and water conservation measure explained. It also provides a large number of explanatory sketches, drawings and photos, of


4

which most can be used in the handouts that will be given during the farmers training. Chapter 3 and 4 discuss how erosion features can be recognized in the field and what are the basic processes. Agronomic and technical soil conservation is discussed in Chapter 5 and 6 respectively. Chapter 7 is concerned with water conservation using the fishpond concept. Chapter 8 discusses the recommended strategy for the short and middle-long term.


5

3 HOW TO RECOGNIZE EROSION

This chapter will illustrate how farmers are confronted with the physical characteristics of erosion in the daily work. For this, it is important to know how to recognize erosion features in the field. 3.1 Symptoms of Erosion This section lists the symptoms that can arise from erosion. Of course, several symptoms can manifest themselves at the same time. 3.1.1 Pedestal Pedestals are seen when soil under grass clumps, roots and small stones stay in place while the soil in between is washed away (Figure 3A and 3B). Stones and similar items protect the soil against the erosive force of the rainfall and eventually settle on a little mound of soil.

3.1.2 Stones on the Surface If a whole layer of soil is washed away, stones will often remain behind. The force of the water is not strong enough to carry the stones away (Figure 3C). The finer particles are removed. If the soil is very shallow, big stones (Figure 3D) or even a hardpan or bedrock may become exposed (Figure 3E).

Fig. 3A Pedestals, typical features of splash erosion

Fig. 3B Pedestals in a fallow field

Fig. 3C Abundant stones in cassava field

Fig. 3D Exposed stones due to topsoil loss; the big stone at the foreground may indicate a very shallow topsoil


6

3.1.3 Exposed Root System Root systems of plants and trees have the ability to retain soil. The fine ramifications of the root system are important for this. If the topsoil layer is washed away, then the roots are exposed, which helps in making a rough assessment of soil loss (Figure 3F and 3G).

3.1.4 Layers of Soil A fine layer of soil is sometimes noticed in the lower lying parts of the field, deposited by slow flowing water. These alluvial deposits (deposits moved by water from elsewhere) of silt can be observed in irrigation furrows too. It’s an indication that erosion may be still in a preliminary stage as little soil has been transported. This fine layer of soil may cover emerging crop over dozens of square meters (see Figure 3H). 3.1.5 Rills Rills are fissures in the soil, which resemble a small gully (< 30 cm deep, [2]). A rill may run into a gully. Especially ploughed fields without a full crop cover are prone to rill erosion, the first step in the development of bigger rills or gullies (Figure 3I). Rills have been observed in fields with slopes of >15% (Figure 3J and 3K). Rills are not always easy to observe. Yet, by identifying them, erosion prone fields/areas can be identified in a preliminary stage, allowing for early soil

Fig. 3E Shallow topsoil in cornfield revealing a water impermeable hardpan at the foreground

Fig. 3F Initial stage of root exposure

Fig. 3G Exposed tree roots


7

conservation measures. Extra attention should be give to train the extension staff in identifying these features.

3.1.6 Gullies Rills that have developed into deeper fissures ranging from a depth of 0.3 m up to several meters are called gullies. As they can bear large quantities of water in a short time, the gully embankments are gradually “eaten” by the fast flowing water (scouring) causing major damages to crops (Figure 3L and 3M), roads and structures.

Fig. 3H Sedimentation of soil material

Fig. 3I Developing rill in a ploughed field with young corn and coconuts

Fig. 3J Rill in field with young corn (slope 15%)

Fig. 3K Well developed rills in cornfield, upon harvest (slope 70%)

Fig. 3L Damaged coconut plantation by scouring gully

Fig. 3M Road collapse through scouring gully


8

3.1.7 Sedimentation in Rivers High sediment loads are transported and deposited in riverbeds. This adversely affects the drainage capacity and it forces the river to change its course by scouring the embankments (Figure 3N). Sediments may be deposited over a large area after heavy flooding creating extensive mud plains in the lower regions (Figure 3O).

3.1.8 Landslides In areas with steep slopes, landslides may occur. For various reasons the stability of a soil can be lost and a large amount of soil slides down the slope (Figure 3P and 3Q). The phenomenon can be observed too if the walls of a gully are undermined by the water stream (Figure 3L). Near roads too, steep side slopes often collapse during heavy rainfall (Figure 3R). At places where a road crosses a depression excessive run-off may accumulate beneath the road’s surface, the foundation. The foundation becomes unstable, consequently reducing the road’s weight bearing capacity (high water pressure causes the soil’s particles to float, a feature often referred to as plasticity, by which it looses its strength). Proper soil compaction during the construction of the foundation and the placement of PVC perforated drains may have avoided the road collapse as shown in Figure 3S.

Fig. 3N River with high sedimentation of alluvial deposits

Fig. 3O Mud plain after severe flooding

Fig. 3P Minor landslide

Fig. 3Q Major land slide


9

water

sediment

3.1.9 Muddy Colored Water Muddy water (yellow, red or brown color) in a stream indicates that soil is being carried along with run-off (Figure 3T). This can easily be illustrated by filling a glass with run-off from that stream and let it stand for a while. The sediments gradually pile up at the glass’ bottom (Figure 3U).

3.1.10 Comparing Fields There may be a considerable difference in topography between two adjacent plots. Sometimes there is an abrupt transition and one field may lie substantially higher than the other (see Figure 3V).

A B

Fig. 3R Slope collapse of road leaves tree roots exposed

Fig. 3S Excess run-off destabilizes road foundation

Fig. 3T Gully with high sediment load

Fig. 3U Sedimentation after 5 minutes (A) and 1 hour (B)

Fig. 3V Elevation difference in two adjacent plots


10

3.1.11 Crop Performance Farm areas situated on slopes usually have different yields in its upper and lower portions. Crop yields tend to be lower on the higher slopes. This is due to a higher loss of nutrients such as organic mater, giving the soil a lighter color. Crops here are more susceptible to drought than those at the lower portions. It can be simply tested in the field by crumbling some of the soil on different places along the slope. Crop yields, such as corn, may gradually decline due to the declining water holding capacity and depth of the topsoil. 3.2 Symptoms of Degeneration of the Environment A number of indicators, which point out to the degeneration of the natural environment, are: Bare hill sides showing ‘slash and burn’ practices. Local farmers convert forestland into agriculture land (Figure 3W). The fragile fertility status of the topsoil is further destroyed as high nutrient extracting crops like corn and cassava are grown, gradually depleting the soil and making it susceptible to erosion. With a declining fertility and depth in topsoil, agriculture land is converted into marginal pasture lands that grow indigenous grasses like cogon and often weeds, a change that does not stop the soil to further erode. Figure 3X shows pastures heavily affected by landslides.

There may be a change in composition of the vegetation over time. Plant species decline as their surroundings impose stricter demands on these as is observed in most of the project area. Vast areas that were once under forest are now covered with cogon, a grass species that easily outcompetes other plants on shallow, infertile soils (Figure 3Y). This grass has a low protein content making it unsuitable for pasturelands.

Fig. 3W ‘Slash and burn’ of primary forest land leaves the fragile, fertile shallow topsoil exposed to non-sustainable agriculture

Fig. 3X Pasture land badly effected by land slides


11

A shortage of firewood may indicate that the carrying capacity of the area has been exceeded.

Fig. 3Y Deforested uplands covered with cogon


12

4 THE EROSION PROCESS Some understanding of the way in which the erosion process takes place is needed to appreciate the usefulness of preventive measures. A few factors will be mentioned which together determine how much and what type of erosion is likely to occur. There are two types of water erosion: splash and stream erosion. Both types are discussed separately, yet they occur at the same time. 4.1 Splash-erosion In splash erosion, the falling raindrops break off small parts of the soil aggregates. The loosened small soil particles fill the gaps between the larger particles and a crust is formed (see Figure 4A). This layer is not easily penetrated by water and air. Hence, crop growth is hindered and water will run-off.

The size and the velocity of the raindrop determine the force of the falling raindrops, both related to the type of rainstorm. If the drops are intercepted by a cover crop the impact will reduce substantially. Obviously, there is a relation between the soil type and the susceptibility to splash erosion. The soil’s resistance to splash erosion depends on: § organic matter content; § moisture content; § type and texture.

Organic matter content Organic matter probably is the most important factor in binding the soil particles. The better the soil particles stick together, the less easy erosion occurs. Clay, lime and iron also bind soil particles. Organic matter is very important for soil fertility and the water holding capacity of the soil. The more water can be absorbed, the less water will run off and cause for erosion. Moisture content Depending on the soil type, the moisture content also determines the stability of the soil. Dry soils can be very hard, but because of that, the water will not easily infiltrate and may cause great run-off. The moisture content of the soil is not the same throughout the year, hence the soil’s sensitiveness to splash erosion varies with time. The sensitive periods are usually at the beginning and at the

Fig. 4A Splash erosion and crusting


13

end of the rainy season when there is, in case of seasonal crops, no protective crop cover. If the soil is very wet, the resistance to splash erosion may disappear as well as. The cohesion between the soil particles declines in a saturated soil. Just before a shower, sizeable clods are apparent in the field and afterwards the topsoil looks like a muddy pulp, certainly for clay soils. Different soil types will react differently. Type and texture The soil texture depends on the size of the mineral particles. In general, the bigger the soil particles, the greater the resistance to splash erosion. Since the texture of a soil cannot be easily changed, however, it does not offer a possibility for controlling erosion. If the soil becomes very fine through tillage operations, the danger of splash erosion becomes greater. The rain no longer breaks the clods and run-off can quickly carry away soil particles. Chapter 5.3 discusses interventions to reduce splash erosion (mulching, cover crops). 4.2 Stream Erosion (rill, gully) Water that cannot penetrate into the soil, runs off to low lying areas, choosing the path of least resistance. This process causes the danger of stream erosion. In stream erosion, the particles that were loosened by the turbulence in the water are carried away by the streaming water (see Figure 4B). In some clay soils particles do not loosen, but area ‘dissolved’ and transported as suspended load. With very low stream velocities this phenomenon occurs. It can be demonstrated by the time it takes before stagnant water loses its muddy color after a rain shower and becomes clear. For the same reason the very top layer of sediment material is always very fine in composition. With fine soil particles washed away, fields become stonier (Figure 4C).

Slowly running water infiltrates into the soil, thus becoming beneficial for the plant. This is more likely to happen in a crumbly rather than a smooth top soil (Figure 4D).

Fig. 4B Stream erosion Fig. 4C Abundant stones in cassava field


14

Of course, the infiltration capacity does not depend merely on the coarseness of the soil. The soil texture (sand versus clay), the organic matter content and a healthy soil organism composition may all encourage infiltration. In general the role of the soil organisms is too little emphasized, but the presence of a healthy soil fauna is an indication that the soil is in good condition. The faster water runs, the greater the scouring force. Rough surfaces can better hold back stream erosion than smooth surfaces. Obstacles such as plant stalks, stones and mulch offer more resistance to flowing water as well. At locations where water collects, the scouring action of the water is greater and rills may be formed that expand with the collapse of sidewalls and scouring until a gully develops [3]. Rill erosion can be also be described as ‘localized small washes in defined channels which are small enough to eliminate by normal cultural methods. Channels are considered to be gullies when they are so large and well-established that they cannot be crossed by farm implements’ [2]. Figures 4E and 4F better illustrate the variations in size and dimensions between a small rill and large gully. .

The amount of erosion mainly depends on the force with which the water acts upon the soil (scouring force) and the degree to which the soil can resist this force. The steeper the slope, the faster water flows and the deeper the stream. A long slope at a high elevation allows a lot of water to accumulate, thus increasing the erosive force. Stream erosion is best prevented by reducing run off. The flowing water should not be allowed to accumulate as they may cause unstable slopes. Chapters 5, 6 and 7 discuss interventions to reduce stream erosion.

Fig. 4D Run-off and infiltration on smooth and rough surface

Fig. 4E, 4F A small rill may develop into a large gully


15

4.3 Combination of Splash- and Stream erosion The combined action of splash and stream erosion is much more serious than the effect they have individually. Erosion caused by run-off appears to increase considerably when raindrops fall in a water layer of a few millimeters. The water is churned around, loosening soil particles, which are then washed away (see Figure 4G).

Note: The term sheet erosion is not used anymore as it conjures up a picture of soil being removed uniformly by an even flow of thin sheets of water [2]. The flow is rarely in the form of a sheet of water of uniform depth, however, and is more commonly a mass of braided watercourses with no pronounced channels. 4.4. Showing the Erosion Process To illustrate how splash and stream erosion influence each other, the following example is given: Case 1: Impact of splash erosion Imagine an unexpected rain shower. From the shelter of a house the clatter of raindrops can be heard on the roof giving an indication of the force with which it is hitting the soil too. Venturing outside, an interesting comparison can be made. It will of course be noticed that the roof remains intact owing to the resistance it offers to the force of the rain. This is quite a different story however if the rain is falling on the bare soil. The force of the falling raindrops can be made visual at places where rain has dropped from a fairly tall height, such as from a roof or for instance a solitary banana palm. A sort of hollow in the soil surface is formed. Look at the stems of plants too. Notice the height to which the soil particles are spattered by the force of the rain. Sand grains are also noticed on the lower sides of corn leaves up to a height of more than half a meter. To illustrate the force of the rain: Look at a puddle with a few millimeters water depth where rain is beating down. This is reddish or brown due to the ‘dissolved’ soil particles. The structure of the soil remains much better in condition if the soil is protected from the direct force of the rain drops (by a cover crop for example). Water can penetrate more easily into the pores of the soil, which have not yet been clogged up by the rain washed particles.

Fig. 4G Combination of splash and stream erosion


16

Case 2: Impact of splash and stream erosion To illustrate protection of the soil against the erosive force of rainfall, put a coin on the soil during a shower and leave it there for a while. Later it will be on top of a little mound. Not only have the pores in the surrounding soil become pressed together, slowing down infiltration, but also a thin layer of soil was transported from the field. Remember that this thin soil layer disappeared over a whole field causing a substantial amount of soil loss which is a result of combined splash and stream erosion. Case 3: Impact of splash and stream erosion Where water accumulates in furrows or on footpaths, fill a glass with that water. Keep it upright for a little while to give the dissolved soil particles time to deposit. This again gives an idea how much soil is being transported with the water (see also Figure 3U). It should be added that a heavy rainstorm might be more erosive than rain falling less heavily over a longer period. 4.5 The Principles behind Erosion Control Measures Knowing the erosion process and how it is related to the condition of the soil, the measures to be taken can be decided upon, based on the following principles: § Reduction of raindrop impact by protecting the topsoil (mulching, cover

cropping, zero tillage); § Improvement of stability (resistance) topsoil by retaining the soil’s

structure (roots tree crops, organic matter); § Reduction of the amount of water which runs-off by establishing

(vegetative) barriers (hedgerows and strip cropping along contours and stone piles);

§ Reduction in velocity of flood water by establishing barriers in gullies, fish ponds etc.

Measures against erosion are described in the following chapters, based on the above-mentioned principles. As was mentioned earlier, the proposed interventions are mainly based on agronomic measures, as it is believed that this will bear the support of farmers. Plant leaves reduce the impact of raindrops and can be used as mulching. Plants reduce the speed of flowing water. Plant and tree roots as well as organic matter improve the structure of the soil and facilitates water infiltration.


17

5 AGRONOMIC METHODS

Agronomic methods focus on soil erosion control measures, which are related to arable farming. It is concerned with crop cultivation as well as tillage operations. Arable farming is an integral part of the natural surroundings. Wood –and grasslands influence arable farming. Four types of agronomic soil conservation methods will be discussed. The principles of these measures were already discussed in Chapter 4. § Land preparation aims on zero/minimum tillage and crop stubble mulching to avoid loosening the soil material (5.1); § Contour and strip farming aim at reducing run-off (5.2); § Cover crops and mulching aim on protecting the soil surface from the erosive force of raindrops, at the same time helping retain the soil’s fertility (5.3); § Cropping Systems aims at good crop growth with optimal use

of cultivated space, water, light and nutrients hence minimizing erosion (5.4).

The proposed methods play a key role in erosion control as its implementation is often relatively easy and cheap. Results do often show off quickly. Each measure may have its advantages and disadvantages, and should be valued on its merits. This may differ significantly for every location. The integration with arable farming makes it likely to be adopted by farmers, more than any other intervention. Agronomic measures contribute considerably to the success of the latter. The selection of crop species depends on, among others, the area’s slope and altitude. In paragraph 5.5 the relation between recommended crop species and slope/altitude is discussed, with an attempt to link it to the first draft agro-ecological zoning (AEZ). Other crop specific information includes rainfall, plant/tree spacing and maintenance requirements.


18

5.1 Land Preparation Techniques known as zero and minimum tillage are briefly discussed here. With zero tillage the land is not ploughed prior to crop cultivation. Holes are prepared, just for planting. In minimum tillage, only places where the crop is going to be planted or sown are prepared, short before planting or sowing. Usually only a single light cultivation of a limited area of the soil surface is used to prepare an area for planting. Existing vegetation and plant residues are largely spared. Stubbles from the former crop can be left in the field. Only the land in between the stubbles is prepared. The purpose of zero or minimum tillage is: § To prevent loosening the soil surface which may become susceptible to soil erosion § Leave crop residues as mulch on ground surface thus preventing splash erosion § Reducing the labor inputs and the extension of the growing season or have an early planting Minimum tillage is especially advisable on soils that easily form a crust on the newly worked soil, in particular soils that are well drained, have a crumbly consistency and a coarse surface. Irrespective of the soil type, the type of annual crop or the use of mulch, plowing on slopes > 18% is not recommended. However, this is commonly observed in the provinces. By plowing along the contours the damage can be controlled. Soil becomes very susceptible to erosion after tillage and before a cover crop has established. During this stage the soil should be protected against splash erosion, by covering it with plant residues (mulching). Only the vegetation around the plant hole is cleared (see Figure 5A). By leaving the stubbles from the previous crop-standing, farmers practice in-row tillage only. Minimum tillage can already be effective in reducing the number of tillage operations from two passes to one pass. Sometimes it also applies to relay cropping whereby the new crop is already sown before the previous one is harvested (see also 5.4.2)

Fig. 5A Cropping between the stubbles of the previous crop


19

5.2 Contour and Strip Farming 5.2.1 Contour Farming Contour farming is a collective name for contour plowing and contour planting, meaning that soil cultivation and planting are carried out along the contours. Too easily false contours are followed making the fields highly erosive after plowing and prior to the full establishment of the next annual crop (Figure 5B). Appendix A provides for guidelines on how to set the contours in a simple and cheap manner, using a wooden A-frame.

Plowing on slopes >18% is not advisable (see also 5.1). If the farmers still persist erosion damage can be controlled if plowing follows the contours rather than plowing down slope (Figure 5C) but, depending on the slope and soil structure, it may happen nevertheless (Figure 5D). The main purpose of contour farming is to prevent water from running off down-slope. It reduces both quantity and velocity of run-off, and hence soil loss. It also increases water absorption. Plants benefit because of increased moisture availability. Clearly, the steeper the slope the higher the risk of erosion. By planting crops along the contours in hedges, vegetative barriers are established that reduce run-off and trap soil particles forwarded by the run-off. It also shows farmers how the contours run. By plowing parallel to the hedge, the farmer will have the assurance that the plough ridges are following the contour line. Obviously, the hedge should not be an obstacle. The land in

Fig. 5B False and true contours

Fig. 5C Plowing down slope

Fig. 5D Plowing along the contours does not necessarily prevent erosion


20

between the hedges is used for annual or perennial crop cultivation, often referred to as alley cropping. The hedge should be uninterrupted (Figure 5E) as gaps easily widen thus leading to gully erosion (Figure 5F).

Extensive research from the MBLRC test farm shows that a number of leguminous species (Figures 5G and 5H) are highly effective in blocking the run-off and trapping soil sediments due to their dense spacing. Moreover, leaves and branches are sources of good mulch and excellent green manure containing substantial nitrogen. Despite its high nitrogen content the leaves are commonly used for fodder which are cut and carried for livestock [4].

The adoption by farmers is still in question as has been the experience of SMAP. The hedgerow concept is perceived as a more or less new technology: The establishment and maintenance of leguminous hedgerows is labor intensive due to its dense plant spacing. The species do not produce any food or cash crop. The MBLR’s recommendation is 1.5 m thick double hedgerows which are spaced 3-5 m by which they “consume” 20-35% of the land, leaving 65-80% of land only for alley cropping [4]: The dense row spacing is recommended to maximize the interception of run-off and sediments and also to produce sufficient leaf biomass for sustainable organic farming, mulching and fodder. Seeds have a market value but their collection is labor intensive. There are alternatives to leguminous species in hedgerows such as grasses like Napier and Guinea grass (Figures 5I and 5J respectively). Unlike cogon grass

Fig. 5E Continuous hedgerow Fig. 5F Broken hedgerows promote gully erosion

Fig. 5G Young hedgerow of Gliricidia Sepium (Madre de Cacao) with dense plant spacing.

Fig. 5H Hedgerows of mixed Flemingia Macrophylla and Desmodium Rensonii


21

that develops creeping stoles, Napier grass is more an upright, deep-rooted grass. Guinea grass is also deep rooted but its clumps are bulkier and have more blades. Both grasses facilitate a rapid establishment of vegetative barriers. The deep rooting and the dense spacing makes them effective in slowing down run-off and trapping soil sediments that are forwarded by the run-off. The sediments accumulate at the upslope side of the barrier forming small terraces over time (Figure 5K). Also both grasses are commonly used for forage. Yet, the adoption by farmers is questionable, for the same reasons as mentioned for the legumes. Moreover, grasses are non-leguminous making the blades less effective for green manure.

Fig. 5K A grass barrier slows down run-off and intercepts sediments [6]

Fig. 5I Napier (Elephant) grass in a hedgerow as an alternative to leguminous species

Fig. 5J Guinea grass in a hedgerow (right side) as alternative to leguminous species


22

5.2.2 Strip Farming Strip farming (or strip cropping) is the cultivation of different types of crops planted in separate strips along the contours. Strips, which do not stand up to erosion well, are alternated with strips, which can withstand erosion usually referred to as buffer strips. In case plenty of land is available, erosion prone strips with corn can be alternated with buffer strips of upland rice. Farmers with small plots prefer the cultivation of one crop, though. Other combinations of alternating strips are grass mixtures and leguminous cover crops. Both strips can serve as pastures. Buffer strips with intercropped perennials and cover crops (coconut/coffee, see also 5.4) can be alternated with strips that grow annual crops like corn or vegetables. Natural vegetation strips are an alternative to hedgerows as well. By leaving unploughed strips of grass and other natural vegetation along the contours, run-off is reduced. At Claveria, Misamis Oriental, farmers developed this technique, using 0.5 m wide grass strips. Farmers at Matalom, Leyte developed a similar technique by plowing 4-10 m wide strips, leaving 0.5-1.0 m strips unploughed with low growing grasses and other natural vegetation. The ploughed strips are then planted while the unploughed grass strips serve as soil traps. Natural terraces form in 1-2 years. This technology, sometimes referred to as strip reclamation, is recommended for slopes between 10-40% [5]. This width of the strip depends on the gradient of the slope and the infiltration capacity of the soil. The principle is that the run-off water in the strips does not reach erosive velocity. Over time terraces will form as soil particles are trapped and accumulate at the upslope side of the buffer strip. If plowing occurs frequently terraces will built up quicker. The process is visualized in Figure 5L.

Strip cropping is a good alternative to hedgerows. It is most effective in combination with crop rotation (see 5.4.1).

Fig. 5L Buffer strips with different stages in terrace development (A, B and C)


23

5.3 Cover Crops and Mulching Where soil is exposed, raindrop impact dislodges particles creating a water impermeable layer thus preventing water to infiltrate. This leads to increased run-off and stream erosion (see also 4.2). A protective cover to the soil surface eliminates the raindrop splash effect with all its detrimental effects. Studies show that surface covers greater than 30% significantly reduce erosion and increase infiltration [5]. Two types of surface covers are discussed: Cover crops and mulching. . 5.3.1 Cover Crops A cover crop is a temporary or permanent vegetative cover of fast growing annual or perennial plants. Creeping legumes are usually used as cover crops. With its dense growth they cover § the ground surface in between spaces of seasonal (eg. corn) or perennial

crops (fruit trees) or § newly harvested land to fallow ----------------------------------------------------------------------------------------------- Legumes. The word legume basically means, “pod bearing plant”, and the most common examples are beans and pulses, commonly used as intercrops due to its shading tolerance. Many plants in the legume family are nitrogen fixing. However, there are also some which don’t fix nitrogen. MBLRC uses as a rule of the thumb that a plant which have nodules on the roots must be nitrogen fixing. The N source is gaseous nitrogen, which is available at 80% in the air. The fixation occurs in the nodules through symbiotic relationships involving the plants and soil organisms such as Rhizobium. High nitrogen concentration are found in the leaves of these plants and it can be made available only for agriculture by the decomposition of the leaves ploughed back to the soil, also referred to as green manuring [7]. ----------------------------------------------------------------------------------------------- The advantages of cover crops are that these: § Minimizes erosion and soil loss. Protective cover against splash and

stream erosion; § Adds organic fertilizer. Annual cover crops are usually ploughed under

when they are still young and succulent, preferably at least two months before the new main crop is sown. Decomposition of plant debris increases the level of organic matter in the soil, especially in the case of nitrogen fixing legume cover crops;

§ Controls temperature. Mulching helps lower the soil temperature by blocking sunlight. This is favorable for seed germination, the crop’s root growth, and for the growth of microorganisms. Moreover it prevents humus to be broken down too quickly;

§ Releasing phosphate. Beans have the ability to release fixed phosphate a phenomenon that is of particular interest, as mentioned before, for the uplands in Southern Mindanao where the soils tend to have a low phosphate content;

§ Limits weed growth. Cover crops suppress the growth of weeds by excluding light from the surface of the soil. This lessens labor costs in cultivation and weeding;


24

§ Food or cash crop. Many legumes (beans, peas and peanuts) are edible crops (high protein source) and these seeds can be sold;

§ Use as pasture. Some cover crop species such as kudzu, centro, forage peanut, desmodium and stylo are appropriate as pasture crops either in between tree crops or as open fields. To stabilize these pastures it is recommended to mix these legumes with grasses such as Guinea that provide for a stable, palatable bulk (see also 5.2.1).

The overriding criteria for selecting the eleven most recommended cover crops was that they are all nitrogen fixing and available in the provinces, hence easy to collect by farmers, making the adoption more likely to happen. Other selection considerations were based on experiences from MBLRC and SMAP (propagation, rate of multiplying, edibility, green manuring, forage) and different literature sources [3, 4, 5, 8, 9, 10]. Table A gives the eleven N-fixing legumes including a number of crop specific features and requirements. Figures 5M-5Q show photos of legumes recommended cover crops.

4

Fig. 5O Stylo [16] Fig. 5P Greenleaf [16]

Fig. 5M Arachis [16] Fig. 5N Kudzu (A) and Centro (B)

Fig. 5Q Hetero [16]


25

Table A Leguminous Cover Crops


26

Grasses may serve as a protective cover as well. Unless these are used in pastures, they are not primarily recommended as green manure due to their limited application: grass decomposes slowly and gives less nutrients to the soil. A few applications of cover crops integrated with annual and perennial crops illustrate their effectiveness in enhancing crop production at the same time protecting topsoil from the erosive force of raindrops [5]. Cover crop interplanted between corn A well-known cover crop in Southern Luzon is the lablab bean. It is intercropped with corn and provides edible pods, fodder and also green manure for the next year’s crop. The bean should preferably be sown together with corn to avoid insect attack. When the corn starts shading the lablab bean, the latter begins to climb the corn stalks, yet will not cover until the corn cobbs are formed and begin maturing (Figure 5R).

Cover crop as fallow crop Velvet bean is an edible legume commonly grown in Indonesia. It is used as a fallow crop in a shifting cultivation system. It is fast growing, increases organic matter, and produces edible seeds. The seed is rich in both crude protein and carbohydrates. This crop is not recommend as an intercrop with an annual due to its vigorous growth. In a crop rotation, soybean planted after velvet bean yields significantly higher than when planted upon either groundnut or grass. Cover crop as fallow material for cereals Too often in upland areas in the Philippines, soils are abandoned because of declining productivity. This is aggravated by monocropping of cereals or cassava with little or no fertilizer being applied. Cowpea is a legume that adapts well to acid/infertile soils. When cowpea is planted, prior to corn or upland rice, it significantly aids in nutrient cycling and the sustainability of corn and upland rice production. Cover crops under tree crops A mixture of two legumes, centro (slow starter) and kudzu is often applied in coconut plantations in the Philippines (Figure 5S). Others combine calopo (fast grower, Figure 5T) with siratro, a perennial drought tolerant legume.

Fig. 5R Lablab bean as cover crop with corn


27

5.3.2 Mulching Mulching is the covering of the soil with organic residues such as straw, corn stalks or other materials such as plastic or gravel. In this paragraph the use of organic residues is discussed only. Research on soil erosion including experiments at MBLRC proves that mulching is one of the most effective measures in reducing the impact of splash erosion caused by falling raindrops as mentioned before. An optimum surface cover with mulch ranges between 70-75% [11]. Mulching has other advantages as well: § Minimizes erosion and soil loss. The mulch serves as protective cover

against splash and stream erosion; § Adds organic fertilizer. Decomposition of mulch increases the level of

organic matter in the soil, especially mulch from nitrogen fixing plants; § Retains moisture. The moisture content of soil remains higher than in soil

without a mulch layer. Crops are therefore vulnerable to water stress during dry spells;

§ Controls temperature. The temperature of exposed soil during daytime is lower where there is mulch applied since sunlight is blocked. This is favorable for seed germination, the crop’s root growth, and also for the growth of microorganisms. Moreover it prevents humus to be broken down too quickly;

§ Increases available phosphate. The mulch layer prevents phosphate in chemical fertilizers from getting into contact with the soil particles that fix the phosphate. Phosphate fertilizers are therefore more effective if they are applied on top of mulch layer than if they are applied on unprotected soil. This feature is particularly useful for the uplands in Southern Mindanao where the soils tend to have low phosphate contents;

§ Limits weed growth. Mulch minimizes the growth of weeds by excluding light from the surface of the soil. This cuts labor costs in cultivation and weeding.

The disadvantage of applying mulch is that it increases the risk of pests especially when mulch comes from corn and sugar cane, particularly if they are not grown alternatively with another crop. Damaging organisms such as stem borers can survive in stems, creating problems the following season. This effect can be minimized by plowing the crop residues into the soil (1), by adding compost or by rotating crops.

Fig. 5S Centro and Kudzu as cover crops underneath coconuts, in between rows of citrus, pineapple and pepper

Fig. 5T Calopo as cover crop in a banana plantation


28

The mulch has to be applied preferably before the on-set of the rainy season, as the soil is then most vulnerable to erosion when rain comes. Seeds can be sown through the mulch layer by making small openings in the mulch through which the seeds are planted. The seeds can also be sown in rows that have been cleared by removing the mulch. The type of mulch used often depends on the rate of breakdown desired and may vary from stalks (Figure 5U), leaves and branches. If an annual crop is to follow mulching, it is recommended to have a rapid breakdown of mulch so that nutrients would be released immediately. In such case, species that have high nitrogen content, such as legumes etc, are very appropriate. Nitrogen accumulates in the leaves making these species so suitable for mulching and organic fertilizer (Figure 5V). A common practice in Southern Mindanao is that farmers apply a rotation of two corn crops with a legume such as mung bean, white/soy bean, black bean, cowpea or peanuts. The corn, pea and bean cuttings are left at site, equally spread over the surface, and not burned as often happens (0.8 kg corn stalks per square meter do usually provide for adequate cover [5]. Stubbles are commonly ploughed beneath the soil. Peanut plants are pulled out of the soil during harvest after which the whole plant including the roots is distributed over the surface.

Cuttings from N-fixing hedgerows species do produce more biomass and the cuttings can be used as fodder as well. It may be desirable, however, to have more persistent mulch for fruit trees like a high fiber, low-nitrogen mulch such as vetiver grass. This slow decaying mulch provides for a more durable cover, which would retain moisture in the soil. Moreover, this mulch does prevent weed species from growing which is particularly beneficial for young trees (Figure 5W).

Fig. 5U Cornstalks are used as mulch covering the surface [7]

Fig. 5V Cuttings of N-fixing hedgerow species are used for mulching, thus adding nutrients back to the topsoil [7]


29

If long rooted vetiver grasses are planted in strips or in between fruit trees, a barrier can be established which will reduce run-off. The on-site cultivation of cogon is not recommended as this grass develops a dense horizontal root system that rapidly spreads all over the field, thus suffocating crops. Therefore cuttings of cogon grass can be applied as mulch only when the mulch does not contain roots. (1) The Programme recommends minimum tillage on sloping fields (see also

5.1). Yet, one of the lessons learnt from SMAP is that farmers who have access to carabaos (water buffalo’s), prefer to plough their fields since this facilitates easy sowing (removing stubbles, breaking topsoil, establishing furrows for seeds). Mulching becomes even more important as a way in mitigating the detrimental effects of tillage.

----------------------------------------------------------------------------------------------- Vetiver grass (Vetiveria zizanioides, locally known as Mora). In many countries under different climates (arid, humid tropics) Vetiver grass is a good alternative to N-fixing trees and shrubs for controlling soil erosion. The effectiveness of Vetiver grass as a vegetative barrier is well understood and extensively described in the international literature. The long vertical roots make this grass species very suitable for establishing hedgerows or grass strips on very steep slopes and can be integrated with cash crops like fruit trees. The grasses filter out the sediments forwarded by the run-off, at the same time build up terraces (see also 5.2.2). Vetiver grasses do not compete with other crops, have low nutrient requirements and are drought resistant. Rats and rhizomatous weeds are kept out and the cuttings can be used for mulch. Other applications are: use as thatch and for reinforcement and stabilization of road and canal banks. The major drawback in using vetiver grasses for soil conservation measures is that it is relatively unknown to the Philippines. Seeds are not readily available in the commercial nurseries. The grass does not yield any edible crop and can’t be used for fodder. Farmers may not be convinced about the effectiveness of vetiver in tackling soil erosion and may find it difficult to establish and maintain grass strips or hedges (spacing 15 cm only) in view of the high labor input. If a serious effort will be made in promoting this grass, the benefits should be visualized to farmers in demonstration plots. In line with Appendix D, which describes how to set up a nursery for general use, Appendix B gives guidelines on the propagation of vetiver grasses [6]. -----------------------------------------------------------------------------------------------

Fig. 5W Vetiver grass cuttings applied as mulch


30

5.4 Cropping Systems The cropping systems described here basically integrate complimentary crops to the traditional monocropping pattern prevalent among upland farmers. These are: 5.4.1 Crop Rotation Crop rotation follows a system of alternating grain crops (e.g. corn) with legumes. Corn takes a lot of nutrients from the soil and it can only be monocropped continuously on very rich, fertile soil, or where large quantity of fertilizers is applied every year. Crop rotation is very much recommended in moist soils. The rotation should include leguminous crops, which could return nutrients in the soil. The reasons for recommending crop rotation are: § It breaks the growth cycle and building up of pests and diseases in the soil

by changing to another crop, which belong to a different plant family. § It fits in additional crops suitable to the planting season and prevailing

weather pattern. The calendar planting of more profitable/market driven crops suits this system.

§ It relieves the pressure of severe nutrient utilization by a single crop that creates an imbalance. The system helps in recycling back nutrients through the green manuring of legume stands.

Below is a typical five-group plant rotation is effective in breaking the cycle of pests and diseases: Group 1 Group 2 Group 3 Group 4 Group 5 Crucifers Solanaceous Cucurbits Roots and Legumes

Plants Bulbs Cabbage -> Eggplant -> Squash -> Carrot -> Mung Bean Cauliflower Bell Pepper Cucumber Onions Peanut Broccoli Tomato Watermelon Garlic String Bean

A three-group plant rotation is less effective but can still be recommended: Group 1 Group 2 Group 3 Cereals Solanaceous Legumes Plants Corn -> Potato -> Peanut Upland Rice Okra Mung Bean 5.4.2 Relay Planting The early introduction and sequential establishment of a second crop while the first is still growing helps reduce the demand for soil cultivation and weeding. The relay crop could also serve as a soil cover following the harvest of the first crop.

A typical relay-cropping scheme involves two annual crops: an upright plant together with a ground cover/bush type of crop that should also be non-invasive e.g. corn with a legume crop e.g. peanuts, mungbean.


31

5.4.3 Planting along Contours and Hedgerows (see also 5.2). The culture of crops along contour lines and in between hedgerows serves primarily to reduce soil erosion and water runoff. This system allows nutrient recycling processes by the incorporation of leguminous nitrogen fixing trees and shrubs; and grasses as hedgerows doubling as soil traps. This living wall of plants slows down the passage of rainwater and arrest soil movement to slowly form natural terraces. Crops are cultivated along lines perpendicular to the slope and in the spaces between the hedgerows. The hedgerows are periodically pruned to prevent shading of the cultured crops. The trimmings are used as mulch, green manure and even fodder for livestock. The Sloping Agricultural Land Technologies (SALT) integrates food, cash crops, forage for livestock and fuel wood/forest trees fitted along a contour-farming scheme. Diverse crops can be planted on the spaces in between the hedgerows/contour lines taking into consideration the slope and the volume of crop required to generate short-term cash needs. The resulting system simulates the natural forest processes of relay planting, nutrient recycling while providing a diverse sustainable income base. 5.4.4 Bush Fallow This system allows the farmland to rest after continuous cultivation. The introduction of leguminous trees and cover crops during the last cropping before the fallow phase blocks any invasion of weeds like Cogon grass (Imperata cyclindrica) and Hagonoy weed (Chremolina odorata). These weeds severely deplete the soil of its nutrients and have harmful effects on other plants. The legumes would improve soil fertility and reduce the length of the fallow period. It also helps reduce the labor for cultivation since these could be incorporated as green manure. It also assists in the control of wildfires. The best form of bush fallow in steep slopes involves a vigorous tree legume with the capacity to regrow rapidly from stump and self-sown seed. Ipil-ipil is one example of a bush fallow species. Ipil-ipil contributes sufficient nitrogen, maintains good soil structure, and draws nutrients from the deeper soil profile. The dense stand of Ipil-ipil and cover crops shades out and precludes most grasses. After allowing the land to rest, the area is slashed at ground level, with the cuttings utilized as firewood, forage and green manure. The area is lightly cultivated and the crop immediately established. The Ipil-ipil begins to regrow but not quickly enough to compete with the crop. It forms a canopy again to shade out the weeds after the crop is harvested and the area can be cultivated again.

Other Intercropping Systems

The growing of more than one crop at a time in the same field provide benefits such as: a. Increased farm output b. Greater variety of food and cash crop produced and there is less risk to the

farmer than if he relies on just one crop. c. Less space occupied by weeds therefore less weeding to be done. d. Helps reduce crop damage caused by pests and diseases.


32

5.4.5 Multi-storey/Fruit Tree Integration Perennials like fruit trees are incorporated to the cropping system not only as a long-term source of income but also as a component of a soil stabilization strategy. The integration of different but complimenting species of fruit tree into an existing industrial crop base like coconut maximize land use, prevents weed invasion and provides more deep rooted perennials to hold the soil. The resulting tree canopy helps in reducing splash erosion and helps water to seep in the soil. Multi-storey farming simulates the forest vegetation by exploiting the shade loving/tolerance characteristics of certain crops arranged in between the layers of the main crop’s canopy. Here are the examples of crop combinations: • Coconut + Abaca or Banana + Coffee or Cacao + Pineapple with Cover

crop • Coconut + Lanzones or Durian + Blackpepper entwined in Madre de Cacao • Coconut + Lanzones + Coffee + Ginger + Taro • Durian + Banana + Citrus + Cover crop • Coffee + Spring Onions • Narra + Abaca (but never in combination with corn since this harbor pests of Abaca) The combination of different annual and perennial crops can be sequentially established with the fruit trees or permanent crops (coconut) planted earlier. This system also allows for the incorporation of multi-purpose trees like Madre de Cacao that serves as a natural trellis for cash crops like black pepper. 5.4.6 Integration of Pasture Cover Crops and Grasses underneath

Permanent Crops/Trees Aside from leguminous hedgerow as source of livestock feed, the area underneath trees could be sown with shade tolerant pasture legumes and grasses were livestock could graze. The introduction of improved species of grass and legumes hopefully will outcompete and replace weed species. However, there should be judicious use of the area by following a ranch system since overgrazing and indiscriminate trampling of ruminants (goats, cattle etc.) render the ground cover function of these pasture crops useless. Some suitable species that can be used for shade tolerant pasture are Greenleaf Desmodium, Stylo, Forage peanut, Ruzi and Guinea grass. Pasture cover crops are established underneath coconut, rubber and coffee stands. 5.4.7 Gradual Integration of Fruit Trees/Establishment of Orchard

alongside Annual Crops The present monocropping system can be improved by the gradual introduction of perennials like fruit trees. The corn or upland rice provides the short-term income while fruit trees assure long-term cash returns. Some of the suitable fruit trees are mangoes, citrus and durian, which are now experiencing high market demand. Table B lists an assortment of recommended crops including crop requirements like rainfall, plant spacing elevation and maintenance. These may fit in one of the above mentioned cropping systems.


33

Table B Crop Assortment


34

Table B Crop Assortment


35

5.5 Crops and AEZ Recommended crops and cropping combinations are related to the first draft agro-ecological zoning there where it refers to slope and altitude. A separate paragraph discusses rainfall. 5.5.1 Altitude and Slope The selection of crop species is largely based on (rather conservative) recommendations derived from the International literature, on the experiences gained from SMAP and the research findings from MBLRC. The first draft AEZ distinguishes three altitude classes: < 100 m, 100-500 m and > 500 m and three slope classes, < 8%, < 18% and > 18%. Combined they form four zones: Lowland < 100 m < 8% Upland 100-500 m < 18% Hilly land 100-500 m > 18% High land > 500 m all slopes Lowlands are beyond the scope of this Programme and will not further be discussed. A more detailed classification in slope classes is required for as the three classes are too broadly defined, restricting appropriate crop recommendations. The following fine-tuning is proposed: Upland 100-500 m 0-3%, 3-8%, 8-18% Hilly land 100-500 m 18-30%, 30-50%, > 50% High land > 500 m 0-3%, 3-8%, 8-18%, 18-30%, 30-50%, > 50% Tables C and D list all recommended crops classified in the three AEZ classes, upland, hilly land and high lands. The slope and altitude class boundaries imply a certain rigidness in the crop choice. Yet, these boundaries are indicative only. Crops that would fall outside a certain class, within limits, may still grow well. These notes will and cannot specify the ‘range of tolerance’. The crop performance much depends on other factors next to slope and altitude, such as the soil’s nutrient status, the microclimate, the water regime and the soil depth. The Programme does not advise to cultivate crops that require for high maintenance on steep slopes, as access for farmers is more difficult here. 5.5.2 Rainfall Monthly and annual rainfall maps were prepared with rainfall classes projected on the map of Southern Mindanao including the boundaries of the provinces (Appendix C). Data covering 30 years records were derived from [12]. In line with the AEZ classification on rainfall [13], for each province the number of dry months (< 100 mm) is determined (Table E). An attempt was made to link


36

Table C Recommended Crops for the Uplands and Hilly Lands


37

Table D Recommended Crops for the Highlands


38

the provinces to the AEZ classification on rainfall, yet this appeared to be difficult as rainfall class boundaries from both sources [12, 13] differ. Moreover, the distinction between AEZ’s rainfall classes C1 and C2 is not rainfall based but on the length of the growing season which is on its turn a crop depending parameter. AEZ’s definition for the dry season for rainfall class A is 1-3 months excluding wet areas where average monthly rainfall never drops below 100 mm like northern part of Davao Oriental and Compastella Valley. Table E shows a decline in rainfall going from north to south. The number of dry months in the southern provinces (southern part of Davao del Sur, South Cotabato and Sarangani) is 7-8, covering the period Aug/Sep till April, whereas in the northern provinces no dry months occur except for April in southern Davao del Sur (Appendix C). A special note is made for the rainfall distribution in Davao Oriental: During the period November-June rainfall north of the coastal towns of Manay/Tarragona is significantly higher than at the area south of these towns, at least 50-100 mm per month. This phenomenon can be explained by the prevailing northeast monsoon winds that bring rain from the Pacific, dropping most of the load north of the two towns leaving the area south relatively dry. Table E Summary of Dry Months

Rainfall requirements for most crops are presented in Table B. Especially for high value fruit tree and commercial crops a match between rainfall requirements and actual rainfall becomes important with a clear eye on the number of dry months. There is a catch though. Dry spells appear to occur more frequent nowadays, a phenomenon often referred to as El Nino. In selecting a location for new planting of high value tree and commercial crops farmers may, if possible, want to select fields nearby perennial surface or spring flows as to facilitate irrigation.


39

6 TECHNICAL METHODS 6.1 Introduction Soil conservation through technical measures aims on controlling run-off and stabilizing slopes. Velocity and quantity of run-off from slopes or in field plots, gullies, rivers and others streams are reduced by obstructing the flow. With lower flow velocities more water penetrates to the subsoil. The scouring effect of run-off declines resulting in less damage to slopes, and road and stream embankments. Interventions to control run-off can be carried out at different levels (6.2) and will be discussed under 6.3. 6.2 Different Levels of Measures The catchment area is the area from which runoff contributes to the discharge at a certain point in a stream or river. The so-called watersheds, the tops of the surrounding hills, determine the borders of this area. The farther downstream, the larger the catchment area and the larger the flow in the stream. The scale determines clearly the extend of the measures to be taken. This seems obvious, yet, it determines a principle aspect of the problem: The number of people involved and, consequently, the level of cooperation. Dwellers in the flood-prone areas will face most problems, yet the basic measures for prevention have to be taken farther up in the hills. Not only can we distinguish here between different methods, but also it is also important to consider the level and the scale on which the measures are taken. These are at: § farm level § slope level § watershed level Obviously, all measures require for regular maintenance in order to be effective in the long run.

Farm level The farmer himself can carry out technical measures at farm level. It aims at a reduction of overland flow to prevent soil loss and the development of rills. Contour farming and the cultivation of grass strips/hedgerows are appropriate cultivation techniques. Guidelines on setting the contours are

Fig 6A Catchment areas [3]


40

provided in Appendix A. Pole barriers and bench terraces are the appropriate technical methods. Main beneficiary is the upland farmer. Slope level Technical measures aim at reducing run-off in gullies and streams. Implementation can be carried out by a group of farmers through self-help or by a contractor for larger works. The most common measures are wattling, dams in streambed, gabions, stone pitching and bamboo planting. Immediate effects of these interventions are to stop further expansion of gullies, stop the scouring process, conserve water and to prevent the collapse of stream/road slopes or embankments. Beneficiaries are farmers that live adjacent to the stream, in particular and road users as well as dwellers that live down slope, in general. Serious gullies and ravines are often found in areas with deep soil profiles and steep slopes. The type of precaution taken to check such gullies depends on their size, the extent of the drainage system and catchment area and the anticipated peak runoff. The farmer himself can usually keep smaller gullies in check. At slope level, the size of the operations generally determines whether a farmer can take action single-handed or together with a few colleagues. However, depending on the nature and magnitude of erosion, a bigger organization will have to be brought in. Apart from the government this can be a cooperative, a communal or a village society. A central government usually becomes involved only if greater interests are at stake, for example the silting up of a dam. Apart from the organization of the recurrent maintenance works, another problem can be the costs and the labor involved. Not only those who benefit directly from the measures should be responsible. Watershed level A watershed level in principle includes both sides of the river. Erosion control is often part of a (civil engineering) development plan. Operations carried out at this level include reforestation, improvements on rivers to prevent flooding in the lower reaches, and also terracing on a large scale. Such a development plan will usually cost a lot of time and money. Large-scale projects will have to be carried out by the government. A well set up water conservation engineering plan for a larger area will make further small scale measures more effective. 6.3 Measures to Reduce Run-off 6.3.1 Pole barriers Pole barriers (or balabag) are commonly used by Filipino farmers in Central Visayas. Ipil-ipil is the main tree species used for balabag. About 1 m long stems and branches are cut and driven in the ground about 0.5m apart, along the contours. The distance between the contours depends on the slope. Longer wooden poles, at least 1m long, are then stacked, on top of each other, behind the stakes to form a fence-like structure. Farmers use twigs, branches, leaves, and other farm debris to reinforce the poles. The balabag is replaced every 4-5 years, by which time the wooden stakes and poles have decomposed and are no longer effective in conserving the soil [5]. Using bamboo has the advantage that the offshoots strengthen the structure, changing the barrier from a man-made, artificial structure into a vegetative one. Pole barriers are constructed in field plots thus blocking over land flow and trapping sediments. Natural terraces may develop over time following the same principle as discussed


41

under 5.2.2. Soil piles up before the barrier. Gradually terraces form. As the slope decreases so will the velocity of the run-off.

6.3.2 Terraces The development of natural terraces using Natural Vegetative Filter Strips (ICRAF, Claveria), hedgerows (SALT, MBLRC) or rock walls follows the same principle. Natural terraces will develop over time.

Terracing is accelerated by plowing along the contours, a practice not recommended in the absence of any kind of barrier (see also under 5.1). The process of building terraces can be speed up by removing soil using hand tools, animal traction or earth moving equipment. Yet, these options are unlikely to be adopted by most upland farmers who lack the necessary resources. Through terracing on steeper slopes (but not more than 40%) the area for cultivation can be increased meanwhile performing sustainable agriculture. On the terraces the superficial run-off is controlled and collected. Water infiltrates into the soil (water conservation).

Fig. 6C Pole barriers, Balabag, Central Visayas

Fig. 6B Farmer establishing pole barriers [5]

Fig 6D Natural terraces develop over time as soils piles up behind the rock wall [3]


42

Stone terraces or rock walls are common in Alcoy, Cebu. Farmers use an A-frame to mark the contours. A 1m wide strip along the contour line is leveled to provide a good base for the wall. A shallow ditch is constructed along the contour to further stabilize the base. Large boulders are used as base materials while smaller rocks and stones fill the upper portions of the structure. Walls are generally 0.5-2.0m high. The base must be strong enough to support the structure. A top width of 50-70cm and a 1m wide base is sufficient for walls with a 1-2m height. To further stabilize the wall and reduce the chance of a washout, farmers plant fast growing legumes (e.g. Gliricidia) and grasses 10cm from the wall and 15-30cm apart within the row.

The width of the terrace depends on the steepness of the slope (Figure 6H, Table F). If the slope exceeds 40% the terrace will be very narrow and the costs of constructing the terraces may exceed the benefits. Vegetative barriers may be more productive [3].

Fig. 6G Stone terraces, Alcoy, Cebu

Fig. 6F Farmer constructing a stone terrace along the contours [5]

Fig. 6H Cross section terrace [3]

Fig. 6E Terraces with seasonal crops like corn without exposing the topsoil to soil ersosion [3]


43

Table F Dimensions Terrace [3] Slope (z/x * 100%) Terrace Distance (x) 1% 40-60 m 2% 20-40 m 6% 15-30 m 10% 10-20 m 40% 5-10 m 6.3.3 Run-off control in gullies Gully control may be severe in areas with deep soils and steep slopes. The water velocity is high and so will be the scouring effect. A deep soil with little cohesion is susceptible to rapid and deep gully formation during heavy rainfall. The purpose of gully erosion is not so much erosion control, but more an attempt to limit the effects of erosion, which takes place upstream from the gully. Obviously, existing gullies should be prevented from developing further. Smaller gullies can be kept in check by farmers constructing fences by weaving branches around pegs, a technique referred to as wattling. The pegs are driven into the streambed of the gully, 50-75 cm apart. Long sprouted cuttings of species such as bamboo are woven alternately around the pegs until a fence like structure us established. The butt ends of the cuttings are bent toward the soil to facilitate rooting. Once firmly established, sprouted cuttings prevent soil wash and damage from the surface runoff. The spacing of wattlings depends on the slope of the streambed but should not be less than 2 m (Figure 6I, 6J and 6K). Soil traps may be dug to reduce the sediment load forwarded by the run-off (Figure 6L).

Fig. 6I Farmer weaving branches around pegs, a technique referred to as wattling [5]

Fig. 6J Cross section of a wattling structure [5]


44

Other obstructions can be made from (1) wire netting supported by wooden poles, (2) a mixture from twigs, poles, stones and bolsters, and (3) loosely heaped stones.

In the somewhat bigger gullies with greater runoffs more solid structures are required for. Check dams from boulders are grouted with a sand/cement mixture. A lower part in the dam may serve as an overflow that facilitates small discharges.

Fig. 6K Check dam constructed by wattling. Note the soil trap [1].

Fig. 6L Soil trap [5]

Fig. 6M Control structures in small gullies [3]

Wire netting

Poles and twigs

Loosely heaped stones

Fig. 6N Dam in stream bed, constructed from boulders and cement


45

6.3.4 Slope and embankment protection At locations where small landslides occur or where road embankments have collapsed, soil stabilization can be accomplished by applying gabions (Figure 6O). Boulders from riverbeds or cuttings from rock are collected and locked in a frame made from wire. Galvanized wire is not sold in the hardware shops in Mindanao. Enterprising engineers use chicken wire, hog wire (used for pig fencing) or cyclone wire (used for fencing) instead. A standard size gabion is approximately 0.5x1.0x2.0 m. Prior to filling the frame it is commonly practiced to close the holes of the wire frame with cornstalks/grasses/bamboo stalks and big clumps (10-20 cm) of hard soil or limestone. Consequently, the gabion is filled with the boulders/stones. Make sure that the smaller boulders/stones fill the voids in between the somewhat bigger ones. The gabions are piled up on top of each after which the structure can be backfilled with soil. Rather than using gabions individual stones or boulders can be piled up on top of each other, a technique also referred to as stone pitching or riprap (Figure 6P). The structure can be enforced by tying the stones through grouting with mortar made from sand-cement or, cheaper, a mixture made from dehydrated/burned limestone with fine sand (1:4 volume). In case no mortar is applied, the structure can be stabilized by filling the voids with a mixture of ash and water.

Bamboo is a fast growing grass specie with a dense rooting system that facilitates proper soil stabilization at steep slopes (Figure 6Q). Using bamboo has the advantage that it can be harvested and used for furniture making, construction material and for constructing tubes for water transport etc. Integration with other crops, though, is not recommended due to heavy shading.

Fig. 6O Gabions for slope protection

Fig. 6P Stone pitching for slope protection

Fig. 6Q Bamboo planting for stream or road embankment protection


46

7 WATER CONSERVATION 7.1 Introduction Water conservation in the uplands mainly relies on the presence of trees with well-developed roots. Root systems of trees (and plants) have the ability to retain soil and water. The extensive branching out of the root system fulfils an important function here. Extensive logging in the project area, though, have caused exposure of the soil in the absence of a protective canopy, leave debris and roots. In pace with the decline of topsoil depth and the absence of deep rooted trees the water holding capacity of the soil reduces over time thus allowing for higher run-off. During dry spells crops are more susceptible to drought now than they were before. To build up the water holding capacity of the soil long term interventions based on new planting of fruit and timber trees are required for. Another more straightforward way to conserve water is by intercepting run-off flow. This can be achieved by establishing physical structures in streams that slow down the surface runoff (Chapter 6), increase infiltration, and divert excess water to storage facilities [5]. The latter will be discussed here in more detail. 7.2 Fishpond, an Integrated Model When excess drainage water from run-off can be intercepted and diverted to ponds, surface run-off can be slowed down and its erosive power reduced. Hence erosion is reduced and water flow is more controlled. To make the establishment of ponds an attractive option for farmers, however, it should do more than merely collect and store water. A good option is to use the ponds for fresh water aquaculture. At MBLRC, a successful cluster of fishponds have been established and operated over the years. In the project area, fishponds have been observed as well. The ponds provide for a high protein source and gives extra revenue to farmers (cash that may be utilized for the purchase of seeds/seedlings). This chapter will mainly focus on the design and construction of the pond (7.3). Most information is derived from [14]. Typical pond management aspects such as spawning, fish health management and water quality control are not covered here as being considered outside the scope of the notes. However, some information is given on fertilizer application. The pond model depicted in Figure 7A comprises of: 1. a fish pond located in the vicinity of a perennial stream or spring, 2. housing for raised animals, 3. vegetable gardens and/or young orchards/fruit tree nurseries 4. an infrastructure of channels (surface water) and/or bamboo poles (spring water)


47

The integration with vegetable gardens and animal husbandry is based on the principle to maximize the use of all available water and land resources: (1) This is accomplished by farm animals converting otherwise unusable food or fodder into edible flesh, while providing manure to the pond. Locating pig and poultry housing in the vicinity of the fishpond will reduce the labor required to transfer the manure to the pond (Figures 7B and 7C).

Inorganic fertilizers usually aim at the application of phosphorous as to ensure a sufficient phytoplankton bloom. For fish culture the best fertilizer is one in which the phosphorous content is 2-4 times that of nitrogen (potassium is usually of little consequences in fish culture). It is only recommended, though, when the manure is having no appreciable effect on phytoplankton growth or when an insufficient quantity of organic fertilizers is available. As to insure complete nutrient dispersal, the compound is to be placed in a porous bag, suspending in the water, hanging from a pole (Figure 7D).

Fig. 7A Integrated Fishpond Model

Fig. 7B Pig/fish integration [14]

Fig. 7C Duck/fish integration [14]


48

Another source of fertilizer may come from termite mounds, placed on poles. The organic material that forms the mound is sliced from the mound with regular time intervals. The chips drop into the water and serve as food for the fish. Also the termites are eaten (personal observation during visit at G.A.Laquihon’s experimental farm at MBLRC, June 2000). (2) The pond may also serve another purpose: its water can be used to irrigate vegetable gardens and young orchards during dry spells. More about this under 7.3. (3) Fish manure (organic), and inorganic sediments gradually build up at the pond’s bottom and can be harvested when emptying the pond, after harvesting the fish. Both fertilizers can be dispersed over the vegetable gardens and young orchards. In summary, the pond serves the following purposes: 1. Intercepts run-off as to reduce soil erosion; 2. Generates food and cash by fish breeding; 3. Supplies enriched water for vegetable gardens and young orchards during

dry spells; 4. Produces organic (fish manure) and inorganic fertilizer (dredge from

pond), to be used in vegetable gardens

Fig. 7D Application of inorganic fertilizer [14]


49

----------------------------------------------------------------------------------------------- Tilapia is considered one of the more favorable species (Figure 7E): Its management is very easy. The fish is a prolific breeder and is very tolerant to low oxygen levels. These are herbivorous and can digest a variety of foodstuffs. Moreover, it has a good market value. The one drawback to Tilapia is the stunting of growth that often occurs due to over breeding which causes crowding and competition for food. Polyculture with catfish is recommended to eliminate the second-generation offsprings that starts to develop after 2 months. Tilapia is harvested after four months. The optimum stocking rate is 3-4 fry/m2 [17] for commercial ponds and 2-3 fry/m2 for low input ponds. The recommended polyculture combinations are Tilapia-catfish, Tilapia-most species of carps and Tilapia-mudfish (Figure 7F).

----------------------------------------------------------------------------------------------- 7.3 Design and Construction of Fishpond 7.3.1 Site Selection The land to be used should be of marginal utility for regular cropping. It is not recommended to use productive land in areas unfamiliar with aquaculture. Suitable locations are in the vicinity of water sources i.e. perennial surface flows or springs. Make sure that the pond is not constructed in the lower regions of a riverbed that is subject to (flash) floods. When selecting a fishpond site, avoid areas having large rocks, substantial deep-rooted vegetation, anthills and/or cracked or broken soils. These are indicators that the pond may be difficult or even impossible to seal, and water would just dry out from the pond. Do not locate ponds where there will be substantial shading of surface waters from surrounding vegetation. Shading will inhibit phytoplankton photosynthesis which results in a reduction of naturally occurring food for the fish and of dissolved oxygen in the water. As a general rule, rectangular ponds should be oriented north to south in order to maximize the sunlight hitting the pond. Sunlight is good for plankton production. The following steps are recommended if planning the construction. Initially, conduct a soil survey of the area. Here the LGU staff comes in to assist farmers. The survey entails digging pits approximately 2 meters deep and analyzing the various layers (or soil horizons, as they are called) that occur from top to bottom. Quite often the soil present at the uppermost horizon will be significantly different from the lower ones.

Fig. 7E Tilapia [14] Fig. 7F Polyculture [14]


50

7.3.2 Soil structure and pH Ideally, the fishpond’s soil should be a clay-loam mixture that minimizes water loss through seepage and provides a fertile environment and nutrient source for the growth of plankton. Sandy soils are too porous to hold water, while strictly clay soils often cause excessive turbidity. Soil pH should be analyzed from the soil samples collected. A pH of less than 4 or greater than 11 is unsuitable for a fishpond, yet these values are unlikely to occur in the project area. The pH can be analyzed by mixing 1 part soil with 2 parts distilled water or rainwater. Use a pH meter or litmus paper to determine the pH of this mixture. The BSWM staff will train LGU staff during the supplementary surveys in assessing the soil’s structure as well as the pH. ----------------------------------------------------------------------------------------------- There are several methods to perform simple hand tests as to assess the soil’s structure. The easiest of which is to try and make a ball from the fine soil (after separating the stones and gravel). If the ball sticks together it has sufficient clay content and a good water holding capacity. Should it crack or break apart it is marginal or poor quality soil. If this test is inconclusive then take another handful of fine soil and wet it so that it sticks together. Squeeze it hard and release. If the soil retains the shape of your hand then it has sufficient clay. If it doesn’t, then it is probably too sandy. The specific texture of the soil can be determined by taking a handful of soil, wetting it, and rolling it into a stick shape about 15 cm long (Figure 7G).

If it doesn’t retain its shape it is probably too sandy and porous for aquaculture. If it retains its shape, then try to form a half circle with it. If you are unable to do this it is loam. If you succeeded making a half circle then continue bending as to form a full circle. If unable, it is a heavy loam. If you have cracks in your circle it is light clay. If there are no cracks, than it is clay. Clay soils will have the best water holding capacity, although loamy soils will have greater fertility. ----------------------------------------------------------------------------------------------- Once the pit is dug, and the soil horizons evaluated, the pit has to be filled with water in the early morning. In the evening, replace the water that was lost to seepage or evaporation and cover the top with boards or leafy branches. The

Fig. 7G Hand test for determination soil structure [15]


51

soil permeability is adequate for fishpond construction if most of the water is present the next morning. Only after the quality of the soil and water are assessed adequately, one may begin the construction of the fishpond. It is essential, however, that the topsoil is removed during construction, be set aside and not plowed under. Use this topsoil to line the bottom of the pond since it is organically rich being the most fertile layer of the soil. This topsoil, lining the pond bottom, will form the basis for the establishment of a productive food chain in the pond. As a rule of thumb, if the topsoil is not fertile enough to support a rice crop, neither is it fertile enough for a fishpond. To minimize the acidity of the pond water, clear all trees, shrubs and vegetation from the inside of the pond during construction. Decomposition of this vegetation will contribute tannic acid to the water, thereby causing water acidity. Over the years ponds tend to fill up with sediment and organic matter. Therefore the fish farmer must periodically remove the topmost layer (10- 15 cm) of soil from the bottom of the pond. Do this only after the pond has been completely dried. Use this nutrient rich organic soil to fertilize any crops under cultivation such as vegetable gardens or young orchards. 7.3.3 Water Sources Optimally, a fishpond should have a dependable source of water sufficient to maintain water levels of 0.5-1.0 meters throughout the year. Potential sources of water include streams, springs and run-off. The latter has a drawback: In theory small ponds may receive adequate water from surface runoff if the surrounding watershed is large enough. As dry spells appear more frequent over the years this water source becomes less reliable, though, hence putting the investment at risk. As a general rule, the pond’s water inflow and outflow should equal the pond’s volume over a period of one month. If the inflow is too high then large amounts of algae may be flushed from the pond. When inflow is too low then the water quality may suffer from oxygen depletion and/or the accumulation of toxic substances. A pond which can be filled and drained by gravity is much more economical than a pond requiring pumps. Pumps are noisy and expensive, and if used for water aeration, these must also have a second pump as a backup. A backup pump system is necessary because if anything should go wrong with the primary pump, a massive fish kill could occur from the resulting lack of aeration. Pumps also require fuel, (gasoline, diesel or electricity) which further increase costs. The favorable topography in the project area easily allows for gravity filling and draining of the pond in most cases, though, making the use of pumps unnecessary. Streams If diverted stream water is used then a constant inflow must be available regardless of fluctuations in the stream flow. Perennial flows are needed to provide constant water supply water throughout the year. A small dam made from boulders can be constructed to lift the water level meanwhile creating a small reservoir in the stream. The dam will gradually strengthen due to the built


52

up of new boulders and sediments forwarded by the stream. Yet, it may not withstand flash floods. To reduce the water pressure the dam can be constructed so that it only partially dams the stream width. In case the discharge substantially drops and water off take is hampered the dam can be extended to its full length. To convey the diverted water from the stream’s intake point to the pond’s intake an unlined channel should be constructed. In places where flow velocities are high causing for scouring of the channel’s bottom or embankment, drop structures may be constructed by using boulders fixed by cement or wire (gabion). In case the topography restricts the construction of channels (steep slopes, valleys) or when the pond is far from the water source, bamboo poles can be used. By boring inside, the nodes are opened and by interconnecting the poles, a conduit is constructed that facilitates water transport (the planting of bamboo is one of the proposed erosion control strategies for protection of river and road embankments). The conduit can be placed on the ground or supported by beams, if appropriate. Springs Springs are best for supplying a consistent volume of high quality water. Considering the relative low discharges and the large distances that are to be bridged between the spring and the pond, bamboo poles are generally suitable for water transport. ----------------------------------------------------------------------------------------------- Spring type. The types of springs that appear in the project area are thought to be of the Gravity Overflow Spring type. Here water flows through the topsoil, restricted to percolate to deeper layers due to the presence of impermeable rock formations or hard pans of mineral soil. The sub-surface flow moves through shallow underground channels also referred to as preferential flow and is forced to move up there where it hits a semi or impervious layer of rock or clay origin (Figure 7H). The variation in discharges in areas with forest is less than in logged areas, as is observed in the field. Moreover, spring water that flows from unlogged areas tend to be more of a perennial character, a feature that can be easily explained: The top soil’s structure is well developed by the abundance of roots and organic material- soil that is held together by the same roots and organic matter. It is able to withhold more water in comparison with a shallow, less developed soil with little organic matter. Water is then more slowly released. E.g. springs at Davao Oriental located in forest-covered areas, tend to be more of a perennial character (steady base flow, less susceptible to dry spells) than those located in logged areas such as at Davao del Sur. ----------------------------------------------------------------------------------------------- The construction of an intake box is recommended to facilitate the interception of spring water, so to avoid the day light point in collapsing or silting up. The box comprises of concrete panels or walls made from bricks, embedded in the soil, covered by a concrete slab, slightly above ground level. The size of the box very much depends on the spring water discharge and the flow that is conveyed to the pond (during SMAP, intake boxes were designed and constructed using 1 cm thick concrete panels with 50x50x70cm dimensions). The box is protected from overland flow by establishing a barrier upslope such as vetiver grasses. The bottom and the lower end of the upslope panels are constructed from boulders and gravel that allow spring water to flow into the compartment. A PVC pipe connects the water filled compartment with the half open bamboo conduit. Excess water may drain via the bamboo overflow pipe.


53

To prevent the compartment from silting up, it has to be cleaned regularly (Figure 7H).

7.3.4 Pond Embankments Pond embankments are constructed large and strong enough to withstand the greatest water pressure exerted on them, high enough to avoid floods, and in such a way that maintenance effort is minimized. Before construction, clean the embankment area of rocks, vegetation and other debris, and remove and save the top 10 cm of topsoil for the pond bottom. Construct each embankment gradually, about 20 cm at a time. Compact each layer before the next layer is put down. The slope of the inside of the embankment (facing the water) should be 1:2 (vertical [rise] over horizontal [run]) if the soil is mostly clay and 1:3 if it is silty or sandy. The outside slope ratio should be 1:1.5 (Figure 7I). In small ponds (less than 0.2 ha) there is a tendency to construct embankment of much steeper slopes to maximize the pond’s surface area and volume but not recommended as this practice, however, results in constant maintenance problems (collapsing slopes). A good method of testing the water holding capacity of the embankment’s soil is to form little balls of soil (about 4 inches in diameter) and allow them to stand in 2 feet of water for 24 hours. If the soil balls haven’t fallen apart during this time then the soil is more than adequate for embankment construction. Plant embankments with grass in order to prevent erosion. Ideally, the type of grass selected should be fast growing so it may be harvested and fed to the herbivorous fish stocked in the pond. Keep in mind though that a thick, heavy grass cover is a potential source of habitation for vermin, such as rats and snakes. Planting of kangkong is also recommended as it provides for fish food.

Fig. 7H Interception and conveyance spring water


54

7.3.5 Pond Size The size of a prospective fishpond should be based on several considerations. Initially, one must determine the purpose of the pond. Will it be used to provide income or simply as an additional source of food for a farm family? If the pond will be used to provide income then one must evaluate the availability of water, potential markets, ease of management, etc. Obviously, the larger the pond, the more fish can be produced. In general, a small farm family easily manages a pond measuring 2,000- 3,000 square meters. Larger ponds will likely require additional expenditures and the hiring of outside labor for maintenance and harvest activities. Ponds smaller than 2,000 square meters do not usually produce enough fish, except in unusual circumstances, to be harvested for profit. These ponds are better utilized to produce food for the family. In such cases, the ponds can be maintained with a minimum of effort and the farmer’s labor can be utilized more efficiently in other endeavors. From SMAP it was learnt that pond sizes have an average of 200 m2 allowing for the cultivation of about 600 fishes (see also 2.1). Farmers that have little or no experience with fresh water aquaculture, yet intend to start a small fishpond, should be recommended to start with small ponds, not bigger than 200-300 m2. Over time new basins can be constructed or existing ones expanded. The pond depth should vary from 0.5 to 1 m. Figure 7I shows the typical dimensions of a small fishpond for starters, based on non-commercial cultivation.

7.3.6 Inlets and Outlets Simple plastic pipe culverts can be used for inlet and outlets for the somewhat bigger ponds. These are easily placed in the embankments. Water flow from

Fig. 7I Typical dimensions of small fishpond for non-commercial use


55

the culverts can be manipulated by blocking the flow using a plastic bag that is tied around the circumference of the pipe. For intercepting debris from the incoming water, a net or permeable bags can be placed around the circumference. The pipe diameter is determined by the discharge. By trial and error the proper diameter can be chosen. Drainage water can be diverted to the natural drainage creeks or to the corrugations in between the beds of the vegetable gardens. The outlet pipe should be installed at the bottom of the pond as to: 1. facilitate the drainage of oxygen free water from the lower part of the pond

(thermal stratification) meanwhile leaving the upper, oxygen containing, water layer untouched;

2. facilitate full drainage of the pond during silt and manure removal. Pipe culverts are uneconomical in very small ponds. In such ponds it is more economical to dig canals through the embankmentss to fill, drain or maintain a consistent water inflow and outflow. In case the pond takes in oxygen free spring water, it is recommended to aerate this water before it enters the pond, by allowing it to drop from a height of roughly 2 m (+ water level pond) on a cascade (top cascade 1 m+ water level pond). The cascade can be constructed from boulders that are usually abundant in the natural streams. The water is forcefully exposed to air by the impact of the drop (splashing) and flow over the boulders that expose the water to air over a relative large surface, allowing for oxygen absorption (Figure 7H).


56

8 STRATEGIC ACTION POINTS The Programme will focus primary on education of and extension to farmers. For this purpose it is envisaged that at soonest, in each barangay, a demonstration plot will be designed and constructed by a leading, motivated farmer, assisted by the Programme. The plot forms an integrated part of the extension activities, as farmers will be more convinced about the benefits of the proposed soil conservation techniques once they see it. The concept has to be further worked out. Bringing farmers from less developed areas to the demonstration plot is another part of the extension activities (cross visits are farmers to farmer exchanges from different municipalities). On the short term extension will aim at a number of simple and cheap methods, which are effective in mitigating soil erosion. Its success will depend much on the willingness of farmers to adopt them. The proposed methods vary from growing cover crops, appropriate land cultivation (minimum tillage along contours, stubble mulching), mulching and green manuring. In particular cover crops and mulching are highly effective when applied correctly. Leguminous cover crops such as the quick spreading forage peanut can be ideally used under annual or perennial crops, either in strips, in between hedgerows (alley crop) or as pastures in combination with mature fruit -and commercial crops. With heavy grazing a mixture of a cover crop and grass is recommended. These simple and cheap methods, referred to as short-term interventions, should be seen in the light of damage control on soil erosion. For food security farmers will definitely resume growing annuals like corn and cassava in the future, perhaps even at a larger scale than at present considering the expected increase in pressure on the available land. It is unrealistic to deny this development. The proposed short-term interventions should be seen in this light. On the medium term (2-5 years from now) a gradual shift from annual to perennial crops (fruit trees intercropped with commercial crops e.g.) is envisaged as it provides farmers with more cash. From a soil conservation point of view this development is encouraged as perennial tree crops provide for a ground cover in the form of a closed canopy and its roots stabilize the topsoil making it less prone to splash and stream erosion. For most farmers the purchase of seedlings is not an option in the absence of cash. If the Programme can assists farmers in setting up and managing small-scale community based or farmer based nurseries, farmers may produce their own seedlings. The concept has to be further worked out with a clear emphasis on the cultivation of fruit and commercial tree seedlings (a guideline, provided by BSWM, on how to establish a tree nursery is attached as an Appendix D). The establishment of vegetative barriers either by leguminous species or vetiver grass is also an effective way in preventing soil erosion. Its relatively rapid establishment (1 year for vetiver, 1.0-1.5 year for the recommended leguminous species) and dense planting makes it a quick and effective method in blocking run-off and trapping sediments. The adoption of hedgerow/vegetative barrier technology by farmers is questionable, though. Despite its effectiveness in preventing soil erosion, its good quality forage (leguminous species), mulch and green manure (leguminous species), its commercial value (leguminous species can provide


57

commercial seeds, oil extracted from vetiver grass) and rodent control (rats avoid vetiver grass) its adoption by farmers is questionable as labor requirements are high for the establishment (dense planting) and maintenance (cut and carry). The hedgerows are not producing any immediate staple or cash crop. Dense spacing between the hedges is required (3-5 m depending on slope) to collect sufficient biomass for mulching and green manure, leaving 25-30% of the fields not productive for any annual or perennial intercrop. Crop diversity and crop rotation of annual crops is advantageous to tackle pests and diseases, a type of organic farming that is well established in the MBLRC test farm. The Programme will point out the advantages of organic farming (green manuring, crop diversity and rotation to cope with pests and diseases in an environmental friendly manner. The use of inorganic fertilizer should not be discouraged in the initial stage, though: Decomposition of leaves takes 3-5 years and during this period the build up of an organic layer is slow. Limited amounts of inorganic nitrogen and phosphate are required as a supplement to green manure and boost biomass production. The generally infertile soils are highly responsive to limited amounts of inorganic fertilizers. At very steep slopes, > 50%, the cultivation of annual or perennial crops is not recommended (although this is still commonly practiced), as these slopes are less accessible for farmers. The Programme supports the planting, of densely spaced, fast growing (e.g. Leucaena 3-5 m/year) forest trees with a commercial value for pulp, charcoal, firewood or furniture, preferably if there are existing wood processing facilities nearby. To integrate water conservation with agriculture, fishponds are proposed to be linked with water intakes from perennial sources (stream or spring). Stream water can be impounded by damming the flow. Excess pond water can be diverted to irrigate vegetable gardens or young fruit/commercial tree seedlings during dry spells. Integration of fishponds with animal husbandry provides for fish food (pig/poultry manure). Blocking and tapping perennial flow water in streams also reduces run-off. Although the fishpond concept gives an excellent opportunity for farmers to supplement their protein requirement and to augment their cash, its impact on water conservation is limited. Water conservation is best served by planting more trees of which its extensive root mass stabilizes the topsoil and enhances the soil’s water holding capacity. Non-agricultural soil conservation methods focus on a number of simple, small-scale infrastructure works (bamboo establishment on road and stream banks, gabions for slope stabilization and protection, dams etc). This type of intervention is more community rather than individual based. The Agricultural Infrastructure Support component will focus on the implementation of different conservation methods of this component at each barangay.


58

The following Short Term Strategies should be developed: § establish demonstration plots § arrange for field and cross visits among farmers § introduce, promote and reinforce the use of cover crops § reinforce minimum tillage along contours § introduce and promote mulching technologies § reinforce the use of green manure The following Medium-Long Term Strategies should be developed: § promote the cultivation of fruit trees (mango, durian, lanzones, mangosteen, jack fruit, marang etc) integrated with established industrial crops (coffee, coconut, abaca) at slopes < 30% § introduce and assist in the establishment of small scale community

and/or individual, farmer managed nurseries with an emphasis on the cultivation of fruit trees § promote the establishment of vegetative barriers such as leguminous or vetiver grass hedgerows § educate farmers on on the disadvantages of monocropping and the benefits of crop rotation in terms of pest and disease control, and nutrient balance § extension on organic farming without excluding modest inputs of inorganic fertilizers § planting of fast growing, densely spaced, forest trees at steep slopes (> 30%) with an eye on the existing demand and infrastructure of wood processing facilities (e.g. leucaena for charcoal, firewood, furniture etc) § promote water impounding structures and maximize their use through fish culture) § small scale infra structure works (bamboo establishment on road and stream banks, gabions for slope stabilization and protection, dams etc)


59

REFERENCES [1] Soil Erosion Management, Proceedings of a Workshop held at

PCARRD, Los Banos, Philippines; Craswell et al, 1984; [2] Soil Conservation; Hudson, 1973; [3] Soil Fertility Management, 3td edition, Agrodok-series No.2, 1998; [4] Salt Agricultural Land Technology, 2nd edition; Palmer/MBLRC; [5] Catalogue of Conservation Practises for Agriculture on Sloping Land; [6] Vetiver Grass, the Hedge against Erosion; World Bank, 1993; [7] Salt Agricultural Land Technology, 1st edition; Palmer/MBLRC; [8] Forage Development Manual, SMAP, Department f Agriculture of the

Philippines, 1993 [9] Resource Book on Sustainable Agriculture for the Uplands; MBRLC,

1990 [10] SALT Extension Package, SMAP, 1992; [11] Soil Erosion and Conservation, Morgan 1991; [12] The Environment and Natural Resources Atlas of the Philippines; [13] Field Manual for Agro-Ecological Zoning; UDP, May 2000; [14] Inland Aquaculture Development Handbook, Blakely & Hrusa, 1989; [15] Training Manual on On-Farm Land and Water Management; AFJ Hamming/BCIAP May 2000 [16] Plant Resources of South-East Asia 4, Forages, ‘t Mannetje & Jones,

1992, Prosea [17] Ang Pag-aalaga ng Tilapya sa Palaisdaan brochure, Extension

Communication Division, Agriculture Training Institute, Department of Agriculture; Philippines

[18] Crop Requirement Tables; UDP, May 2000; [19] Fruit and Vegetables, MacDonald &Low, 1990 [20] Rainfall Records from Mindanao, National Institute of Climatology,

Pagasa, The Philippines


60

APPENDIX A


61

CONSTRUCTION and USE of A-FRAME for SETTING CONTOUR LINES [9] Construction of the A-Frame One does not need to have expensive soil surveying equipment to locate contour lines. This chapter discusses the use of a simple A-frame that can easily be made by the farmer using locally available materials. The steps in making the A-frame are as follows: 1. Secure the following materials: 3x wooden or bamboo poles with a 1.5 inch

diameter (two should be 2.1 m long and one about 1.2 m; sturdy string; rock about the size of a fist (Figure A1).

Fig. A1 Components A-frame [9]

Tie or nail the two longer poles at one end, about 10 cm from the end. Make sure they are securely fastened, as they will make the legs of the A-frame. Make notches on the points of contact so that the poles will not slip (Figure A2). Spread the legs and brace with the shorter pole to make a figure “A.” Tie or nail the crossbar (about 10 cm from each end) to the middle of the legs of the “A”. The crossbar will support the legs of the frame and will serve as guide in marking the level ground position. Tie one end of the string to the point where the two legs of the A-frame are joined. Tie the other end of the string to the rock or any object for weight. The rock should be heavy enough so that when it is suspended, it will not sway with the wind. The rock should hang about 20 cm below the crossbar (Figure A2).

Fig. A2 Constructing the A-frame [9]


62

Calibrating the A-Frame 1. Locate a reasonably level ground and place the A-frame in an upright

position. Mark the spots where the legs A and B touch the ground. Then, mark the crossbar where the weighted string passes it (Figure A3).

Fig. A3 Calibrating the A-Frame [9] 2. Reverse the position of the A-frame’s legs such that leg A is exactly on the

same spot where leg B was and vice-versa. Again, mark the crossbar where it is crossed by the string. If the two marks exactly coincide, this means that you have the midpoint on the crossbar and that the A-frame is standing on level ground. If the two marks are separate, indicating that the frame stands on non-level ground, make another mark at the midpoint between them (Figure A4).

Fig. A4 Calibrating the A-Frame on non-level ground [9] 3. To check the accuracy, move one leg around until the string passes the level

point of the crossbar. Mark the point where the adjusted leg touches the ground. Reverse the placement of the legs of the A-frame. If the string passes the same point, the level position has been located.

Marking the contour lines 1. Cut tall grasses and remove other obstructions. Use two people making the

work much faster and easier. One will operate the A-frame while the other marks the located contour lines. Stalks or wooden pegs can be used the mark the contour.

2. Begin near the highest point of the field plot. Drive the first peg at the

boundary and position one of the frame’s legs (A) beside it.


63

3. Place the other leg (B) such that the weighted string passes through the midpoint of the crossbar indicating you have found the contour.

4. Move the A-frame by turning leg A around peg B (in most cases the turn

will be more or less 180 degree turn, but not necessarily), placing leg A there where the string passes the midpoint mark. Mark the location of leg A location by a peg. Spacing between the two pegs is now 4 m. Repeat the exercise for the other leg and so on. Follow this procedure until you reach the other side of the field (Figure A5 and A6). Spacing between two pegs very much depends on the slope. The smaller the spacing, the more accurate the contour is set.

Fig. A5 Setting the contour [9]

Fig. A6 Contours marked by wooden pegs 5. The spacing between two contours should be based on the vertical drop

meaning that in the case of steep slopes the spacing between two contours is smaller. A level instrument or more easily using the “eye-hand” method, can determine this drop. In this method, a person stands perpendicular to the slope along a contour, which has already been set. Facing uphill, he then holds his arms straight out in front of him, forming a ninety-degree angle between his arms and body. He then sights over the tips of his extended fingers into the ground before him. This sighting will be the point to begin the next contour (Figure A7). For setting contours, as a rule of the thumb a 1.5 m drop suits the spacing between two contours quite well, irrespective of the slope.

Fig. A7 Determining the vertical distance between contour lines [9]


64

APPENDIX B


65

ESTABLISHING a VETIVER GRASS NURSERY [6] To find a source of vetiver grass, first check with the local herbarium (located in the university, or botanical gardens, or agricultural department) to determine if it has any specimens of Vetiveria zizanioides. If they have, withdraw the specimen sheet, and in the bottom lefthand corner there should be a small map showing where this particular specimen was collected. This will show you what the plant looks like; give you the locality where it was found, and if the collection was done correctly, it will tell you the local name of the plant. If the plant is unknown, contact a World Bank agricultural staff member for planting material Assuming you have a source of planting material, dig out the clumps of vetiver, cutting the roots off about 20 cm below the surface. Cut off the leaves about 30 cm above the roots, and break the clump into planting pieces, or ‘slips’of about five tillers per slip, taking care to discard dead or seeded tillers. Single tillers will suffice if you are desperately short, but it is better to plant a small clump. The nursery is best located in an irrigated field, which will encourage the plants to grow very rapidly. Within six months you should have enough planting material to protect 100 ha of land (20 km of vetiver hedges). Prepare the nursery bed as you would for any field crop: plow it, cultivate it, and get rid of the weeds. The seedbed needs not be smooth, as the vetiver seedlings (slips) are extremely hardy. Irrigate the plot thoroughly, and then transplant the slips as you would transplant rice. The vetiver slips are spaced 40 cm apart. It does not matter if it rains after planting and inundates the slips. The plant will not be affected. This wide spacing gives each plant ample room to ‘tiller,’ or produce more planting material. There is no set planting distance and with experience you may develop a planting distance suited to local conditions. The planting material should be brought to the nursery at least six months before the planting season so that it is available at the beginning of the wet season. Once all the slips have been planted in the nursery, fertilizer can be applied if necessary. Plants grow faster and produce more tillers in less time if they are fertilized. Generally we use phosphate fertilizers in combination with some form of nitrogen; for instance, sulphate of ammonia super phosphate, or urea super phosphate, or diammonium phosphate, whatever is available and cheap in the nitrogen-phosphate range. You may even use manure on the nursery beds. The more optimum amounts of fertilizer applied according to the needs of the soil, the more planting material will be produced in six months. In the first two months, when the plants are getting established, weed the beds to keep the weeds under control. Once the plants have started to grow vigorously, keep them trimmed to about 50cm, and use the cut leaves to mulch between the rows and keep the weeds down. Trimming encourages ‘tillering’ and produces more planting material in a shorter period. If the plants are allowed to flower, tillering is reduced. After six months there should be between 80 and 100 tillers per plant, which can be used as planting material. Thoroughly soak the plants to make it easier to lift them out of the ground. Quite often, it takes a two-man team using a strong fork, or pick, or even a bar (crowbar) to remove the tillers from the ground. One man levers the plant out of the soil, the other pulls the top of the plant toward him. Once sufficient roots are exposed, they can be cut 20 cm


66

below the surface, and pulled out by the other team member. Now the clump can be broken up into planting pieces for transport to the field. When harvesting, leave three or four tillers in the ground from each clump to renew the planting material. Fertilize and irrigate the remaining plants, using all the trash from the harvest to mulch the beds. Succeeding harvests may be possible in four to five months. Transporting the material to the field is no problem. Trim the slips as stated above - 30 cm of leaves/20 cm of roots, both trimmed with a machete - put them in grain bags or throw them in the back of a truck. The plants can stand a lot of rough handling, and can be left unattended for 10 days. It is always better if you can plant them the same day, but if they have to be transported over great distances or stored, the losses will be negligible. Planting should be done at the very beginning of the wet season.

Fig. B1 Nursery with rows of vetiver grass, growing in clumps


67

APPENDIX C


68

RAINFALL Rainfall data are derived from the National Institute of Climatology, Pagasa [20] and the Environment and Natural Resources Atlas of the Philippines [12]. Mean monthly rainfall are depicted in graphs, for five rainfall stations in Mindanao i.e. Hinatuan, Davao City, General Santos City, Malaybalay and Cotabato City. Records cover 34 years, i.e. 1951-1985 and 1961-1995 [20]. For Davao City and General Santos City separately rainfall data from both periods are compared. No significant differences are found.

Comparing rainfall data between the five stations show major differences, spatially as well as over the seasons. A first glance reveals that going down from north to south rainfall drops substantially, from 4168 mm annual rainfall at Hinatuan (just outside the project area, north of Davao Oriental) to 1750 mm for Davao City and 960 mm for General Santos City in the far south. This trend is better illustrated in Figure C1 showing the mean annual rainfall in classes, depicted as a colored map of Southern Mindanao [12]. Mean monthly rainfall is presented in Figures C2-C13.

Mean monthly rainfall

0

50

100

150

200

250

Jan

MarMay Ju

lSep Nov

Month

Rai

nfa

ll in

mm

Davao, annual 1793 mm (1951-1985)Davao, annual 1750 mm (1961-1995)


0

20

40

60

80

100

120

Jan

MarMay Ju

lSep Nov

Month

Rai

nfa

ll in

mm

GenSan, annual 955 mm (1951-1985)GenSan, annual 960 mm (1961-1995)


0

100

200

300

400

500

600

700

800

Jan

MarMay Ju

lSep Nov

Month

Rai

nfa

ll in

mm

Davao, annual 1750 mm (1961-1995)GenSan, annual 960 mm (1961-1995)Hinatuan, annual 4168 mm (1961-1995)


0

50

100

150

200

250

300

350

Jan

MarMay Ju

lSep Nov

Month

Rai

nfa

ll in

mm

Davao, annual 1793 mm (1951-1985)Malaybalay, annual 2537 mm (1951-1985)Cotabatu, annual 2238 mm (1951-1965)


69

1000 2000 3000 4000 5000 mm Rainfall station: D = Davao City

C = Cotabato (Maguidanao) M = Malaybalay (Bukidnon) H = Hinatuan (Surigao del Sur)

G = General Santos City

Fig. C1 Mean annual rainfall in mm (1961-1990)


70

Fig. C2 Mean rainfall January Fig. C3 Mean rainfall February

Fig. C4 Mean rainfall March Fig. C5 Mean rainfall April Mean monthly rainfall in mm (1961-1990)

0-50 50-100 100-200 200-300 300-400 400-500 source: Environment and Natural Resources

Atlas of the Philippines, ECPG, 1998


71

Fig. C6 Mean rainfall May Fig. C7 Mean rainfall June

Fig. C8 Mean rainfall July Fig. C9 Mean rainfall August Mean monthly rainfall in mm (1961-1990)




72

Fig. C10 Mean rainfall Fig. C11 Mean rainfall October September

Fig. C12 Mean rainfall Fig. C13 Mean rainfall December November Mean monthly rainfall in mm (1961-1990)




73

APPENDIX D

government of the philippines department of … technical notes on swc.pdf4.5 the principles behind...

Documents