Main contributors: A.N. Atta-Krah, B.T. Kang
3.0 Performance objectives
3.1 Introduction
3.2 Guidelines for hedgerow establishment
3.3 Guidelines for hedgerow management
3.4 Feedback exercises
3.5 Suggested reading
Unit 3 is intended to enable you to:
1. Describe procedures for planting trees by the direct seeding method, including planting depths and seed pretreatment procedures.2. Explain when inoculation of MPT seeds may be required, and when inoculation would not be required.
3. Describe procedures for planting trees from seedlings or cuttings.
4. Discuss factors affecting the optimal spacing and orientation of hedgerows.
5. Sketch the layout of IITA's prototypical alley farming system, and indicate appropriate adaptations for various environments.
6. Anticipate common establishment problems and recall the relevant preventative or curative procedures.
7. Describe appropriate techniques for pruning hedgerows, and understand the principles that apply to the scheduling of prunings.
8. Explain the roles played by mulching, fertilizer application, and short fallow periods in the management of an alley farm.
9. Explain alley farming's contributions to weed control.
From a technical viewpoint, obtaining the full benefits from an alley farming system depends on the following factors:
· correct choice of tree species,
· successful hedgerow establishment,
· efficient hedgerow management.
The first factor, choice of MPT species, was covered in the previous chapter. This current chapter will review the recommended practices for establishing and maintaining the hedgerows. The recommendations are based on alley farming research to date.
By reducing trial and error, the recommendations in this chapter can save time and effort for alley farming researchers and practitioners. Yet, the recommendations are certainly not cast in stone. Alley farming is a young science, and its techniques require continuous development. Many aspects of hedgerow establishment and -management offer fruitful topics for new research. For example, AFNETA/NARS research projects are seeking to fine-tune aspects of tree spacing, pruning regime fertilizer application, and following, among other techniques.
Leucaena leucocephala and Gliricidia sepium are used as examples of hedgerow species throughout this chapter. The two species are the most popular and best-researched trees for alley farming in the tropics. However, it bears repeating that Leucaena and Gliricidia will not always be the best choice, particularly when the local site lies in a semi-arid or highland zone, or has acidic soils.
3.2.1 Land Preparation and Timing of Planting
3.2.2 Planting by Direct Seeding
3.2.3 Seed Planting Depth
3.2.4 Seed Pretreatment Procedures
3.2.5 Inoculation of Legume Seeds
3.2.6 Planting with Seedlings or Cuttings
3.2.7 Spacing and Orientation of Hedgerows
3.2.8 Humid Zone Prototype with Leucaena and/or Gliricidia
3.2.9 Variations on the Prototype
3.2.10 Fertilizer Requirements during Establishment
3.2.11 Common Establishment Problems
3.2.12 Hints on Successful Seedling Establishment
Hedgerows can be planted on ridged (heaped) or unridged land. The land should be cleared of all weeds just before planting. For experimental trials, intensive site preparation is often practiced, including land preparation such as plowing, subsoiling, harrowing, leveling, terracing, and/or irrigation.
The trees should be planted at the start of the major rainy season. If planting must follow a food crop, as is often the case, it should be done as soon as possible in order to minimize shading during establishment, when the seedlings are prone to competition from fast-growing weeds. In the case of alley farming with maize, the trees may be sown immediately after the maize crop.
Trees and shrubs in hedgerows may be established from seeds, seedlings, or stem cuttings, depending on the species used. Direct seeding is feasible where annual rainfall is 1200 mm or more, and the growing season lasts a minimum of approximately 6 months. Seeds carried in pockets or small bags can be planted by hand or with simple planters. Direct seeding is the cheapest and simplest method of hedgerow establishment. However, seeds tend to have short longevity (e.g., Acioa barteri) and to be unavailable at certain times of the year. An additional limitation is that the seedlings which sprout from direct seeding are usually very small during early establishment, and must be given extra care and protection.
One cheap and easy way of establishing Leucaena hedgerows is by direct seeding in the same row as a crop such as maize. With this method of establishment, no extra weeding cost is incurred for the Leucaena during early growth. The slower-growing Leucaena can also benefit from the residual fertilizer applied to the maize crop. At the time of maize harvest, the Leucaena would normally have reached a height of 5075 cm and be able to outgrow any weeds.
When the direct seeding method is used, special attention should be paid to:
· seed planting depth,
· requirements for seed pretreatment, and
· requirements for seed inoculation with rhizobia
Figure 3-1. Recommended planting depths for maize, Leucaena, and Gliricidia.
Deep seed placement hampers germination and emergence, particularly of Gliricidia. Ideally, depth of planting should be about 2.0 cm for both Leucaena and Gliricidia. The number of seeds per hole depends on the germination percentage of the seeds but generally, for seed batches with 75% germination or more, two or three seeds should be planted per hole. Figure 3-1 illustrates the recommended planting depths.
Table 3-1 Seed pretreatment and rhizobium inoculation requirements for certain MPTs commonly used in alley farming research
|
Species Name |
Seed Pretreatment |
Rhizobium Requirement |
|
Acacia auriculiformis |
A |
Nodulates freely |
|
Acacia senegal |
Overnight soaking |
Nodulates freely |
|
Albizia lebbeck |
A, B |
Cowpea miscellany |
|
Calliandra callothyrsus |
A |
Nodulates freely |
|
Cajanus cajan |
None |
Nodulates freely |
|
Cassia siamea |
A, B |
Does not nodulate |
|
Flemingia macrophylla |
None |
Nodulates freely |
|
Gliricidia sepium |
None |
Nodulates freely |
|
Inga juniciul |
None |
|
|
Leucaena leucocephala |
A, B rhizobia |
Fast-growing |
|
Prosopis juliflora |
A, B |
Nodulates freely |
|
Sesbania sesban |
A, B |
Reciprocal affinity between cowpea and soybean rhizobia |
|
Tephrosia candida |
None |
Nodulates freely |
A. Hot water treatment
B. Conc. sulfuric acid treatment
The seeds of most legumes have hard, water-resistant coatings. The seed dormancy must be broken to allow maximum germination rates. Seed pretreatment procedures, called scarification, are required for species such as Leucaena or Cassia, but not for others such as Gliricidia. Table 3-1 provides information on pretreatment requirements. Scarification can be done mechanically (manually), or by hot water or acid treatments.
Mechanical Pretreatment
Seeds may be rubbed against an abrasive surface such as sand paper or an iron file. Care should be taken not to damage the seed embryo. Mechanized treatment is tedious for large numbers of seeds.
Hot Water Pretreatment
The simplest and most frequently used method of scarification is the hot water treatment. However, it may give erratic results. Boiling (100°C) water is poured onto seeds and the mixture is stirred for 3 or 4 minutes. The seed: water ratio should be 1:2 by volume. Effective treatment requires a minimum water volume of one liter. The water is then poured off and the seeds dried in the sun.
Alternatively seeds may be immersed in twice their volume of boiling water and allowed to soak in the gradually cooling water for 12-24 hours. The water should not be heated after seed immersion, since seeds will be killed by prolonged heating.
Acid Pretreatment
Acid treatment gives consistent results and is more reliable, but it is dangerous and expensive. Seeds are treated for 60 minutes with concentrated (commercial grade) sulfuric acid (98%, 36 N) at a seed to acid ratio of about 10:1 by volume. Following treatment the seeds are immediately rinsed in running water to remove traces of acid and dried for storage.
The leguminous MPTs preferred for alley farming, such as Leucaena and Gliricidia, rely on rhizobium bacteria in the soil to fix atmospheric nitrogen. Like all legumes, they develop root nodules where nitrogen fixation occurs - but only in the presence of a suitable strain of rhizobium bacteria (See Table 3-1). In cases where a leguminous hedgerow species is being introduced for the first time in an area, artificial inoculation may be necessary to guarantee rapid establishment.
When to Inoculate
There are five conditions under which soils may be devoid of rhizobia and warrant inoculation:
· in the absence of the same or a symbiotically related legume in the immediate past land use history;
· if poor nodulation occurred when the same crop was grown previously;
· when the legume follows a non-leguminous crop in a rotation;
· in land reclamation;
· when environmental conditions are unfavorable for rhizobium survival (e.g., extremes of pH).
How to Inoculate
A simple and inexpensive way to introduce the appropriate rhizobium is to mix the seeds before planting with soil collected from around established trees of the same species growing nearby.
Alternatively, seeds may be mixed with a rhizobium culture, either in a laboratory or in the field. Researchers may obtain rhizobia by:
· Purchasing an inoculant packet from a commercial producer,
· Requesting rhizobia from a culture collection (e.g., at a research institute), or
· Isolating rhizobia from nodules, dried root material, or soil.
Certain types of commercial inoculant packets can be readily used by field workers and farmers. More detailed information on inoculation techniques is provided in the Appendices.
The use of seedlings or cuttings is profitable for quick establishment, and may be required due to the above-mentioned limitations of direct seeding. In sub-humid or semi-arid environments with less than six rainy months and 1200 mm of annual rainfall, establishment by seedlings is preferred.
The advantages of planting with seedlings are that, in general, seedlings are tall enough to compete successfully with weeds and they require less care and protection during early development. A hedgerow planted from seedlings will attain a large size quickly. Disadvantages include the need to establish a nursery, the difficulty and expense of transporting seedlings, and the requirement for water - which should be applied immediately after transplanting.
Seedlings are grown in nursery bags from seeds planted 8-10 weeks prior to the rainy season. The seedlings should be transplanted (with or without bags) during the major rainy season as soon as the rains have stabilized. Nursery procedures are reviewed in Unit 2. In some instances, bare-root seedlings can be used with a high degree of success in the humid zone with species such as Leucaena.
The use of stem cuttings is feasible for some species such as Gliricidia sepium and Erythrina spp., but is generally less preferred when direct seeding is possible. Establishment of an alley farming system generally requires a large number of cuttings. This can be costly, inconvenient, and impractical if parent trees from which cuttings could be obtained are not locally available.
The position and spacing of hedgerow and crop plants in an alley farming system depend on plant species, climate, slope, soil conditions, and the space required for the movement of people and tillage equipment. Ideally, hedgerows should be positioned in an east-west direction so that plants on both sides receive full sunlight during the day. The spacing used in field trials usually ranges from 4 to 8 meters between the rows and from 25 cm to 2 meters between the trees within rows. The closer spacing is generally used in humid areas and on sloping lands. The wider spacing is suitable for very humid areas (where radiation is limited) and in the subhumid or semi-arid regions (where moisture is limited). See Table 3-2.
Position and spacing of hedgerows may also be affected by slope and the placement and design of soil and water conservation structures, where these are combined with alley cropping. On sloping land, hedgerows should always be placed on the contour (Figure 3-3). If this means that they do not have desirable east-west orientation, then they may need regular trimming to prevent excessive shading of adjacent crops.
Figure 3-2. Alley farming on sloping land. Hedgerows follow contour lines.
If the land slopes steeply (e.g., on hillsides) the hedgerows will be spaced closer together. Also, on steep slopes the contour lines should be determined more accurately than can be achieved by eye alone. A simple A-frame device is adequate for establishing contour lines. (Refer to the Appendices for information on use of an A-frame and other simple techniques for planting along contour lines).
Based on years of experimentation, scientists at IITA have developed a prototype for alley farming with Leucaena and Gliricidia (Figure 3-3). The system performs optimally in the humid tropics, at low altitudes, and on non-acid soils.
Hedgerows can be established economically by planting seeds of Leucaena or Gliricidia with a food crop at the beginning of the rainy season. Plant Leucaena and Gliricidia seeds, as shown in the diagram, in rows between the rows of a crop such as maize. The rows of Leucaena may also be planted with maize as shown. (This arrangement is for the first year only; as Leucaena grows, there will be no more space for maize plants in the hedgerow itself). The trees can be planted at the same time as the maize seeds or shortly after the maize emerges.
The recommended spacing of Leucaena and Gliricidia rows for smallholders is 4 m, with 25 cm between planting holes. Using this spacing, and planting 3 seeds per hole, requires 1.7 kg of Leucaena seeds and 2.5 kg of Gliricidia seeds per hectare. In the subhumid zone, an alley width of 6 m is better. For tractorized operations, an alley width of > 9.0 m will be more convenient.
Figure 3-3. Arrangements for planting Leucaena and Gliricidia hedgerows with maize to create alleys 4 meters wide.
Mixing Leucaena and Gliricidia (or any two MPT species) in the same hedgerow is not recommended, as one species will tend to dominate the other. However, it will be advantageous in some circumstances to plant alternate rows of Leucaena and Gliricidia, for example, in alley farming with livestock.
The main thrust of current alley farming research in Africa is the adaptation of the humid-zone, non-acid soil prototype to other environments. The key experimental issues in this research effort are:
· choice of MPT species for hedgerows,
· choice of spacing between hedgerows, and
· rationale for establishing hedgerows in crop land.
The issue of MPT choice was covered in Unit 2, where it was noted that species other than Leucaena and Gliricidia would be more suitable for acidic soils or a dry environment (e.g., Flemingia macrophylla or Acacia spp., respectively). Necessary variations in inter-row spacing were also touched upon in earlier sections. The recommended spacings for different environments are summarized in Table 3-2.
Researchers have recognized that a farmer's rationale for establishing an alley farm also varies between agroecological zones. An important case in point is the semiarid zone, where the need to minimize competition for water compels farmers to establish hedgerows at wide spacings of 6-8 m or more. The resulting low density of trees diminishes the value of the hedgerows as a source of mulch. There may not be enough prunings available per hectare to make a significant impact on food crop yields. However, hedgerow prunings could still provide an important source of supplementary fodder for livestock production, which is commonly an important farm activity in the semi-arid zone. The widely-spaced rows could also provide excellent protection against wind and/or soil erosion.
Table 3-2 Recommended inter-row spacings for various environments.
|
Environment |
Inter-row Spacing | |
|
Smallholder Operations |
| |
|
|
Perhumid Zone (overcast) |
6 m |
|
|
Humid Zone |
4-6 m |
|
|
Subhumid Zone |
4-6 m |
|
|
Semi-Arid Zone |
8-12 m |
|
Tractorized Operations |
> 9 m | |
Alley farming in dry areas or on acidic soils may benefit from the modification of establishment and management practices (e.g., a lighter pruning regime in semi-arid zones). Furthermore, in areas where competition between hedgerows and crops for water and nutrients is of concern, the introduction of new practices such as root pruning may become important. Normal plowing of the alleys in preparation for crop planting accomplishes tree root pruning. Special root-pruning procedures tend to be prohibitively labor-intensive.
The major differences between humid-zone and semi-arid zone prototypes are summarized in Table 3-3.
Table 3-3. Alley farming prototypes.
|
Humid Zone |
Semi-Arid Zone |
|
1. Narrow alleys (4-6 m) |
1. *Wide alleys (6- 8 m or more) |
|
2. Leucaena Gliricidia, etc. |
2. *Acacia spp., Prosopis spp., etc |
|
3. Hedgerow prunings for mulch/green manure/fodder |
3. Hedgerow prunings for fodder |
|
4. Hedgerow for soil erosion/runoff control |
4. Hedgerows/shelter belts for wind erosion/soil erosion/runoff control |
* Tentative recommendations.
On fertile land, such as newly cleared fallows, fertilizer may not be necessary. However, on moderate to low fertility soils, fertilizer is needed to boost initial growth of the tree seedlings. This should be applied 4 to 6 weeks after planting, as a side-dressing of a 15-15-15 N:P:K compound fertilizer at 15-20 grams of fertilizer per seedling or 300-400 grams per 5-meter row (equivalent to about 150 kg fertilizer per ha). This fertilizer application may not be necessary if the companion crop is fertilized.
Leucaena is highly prone to attack by rodents and termites. Although it is difficult and expensive to control termites, rodent attacks can be reduced by clean weeding. Gliricidia is susceptible to grasshopper attack during the dry season. Older leaves seem to be preferred to young emerging leaves. It is also highly susceptible to aphid infestation in the dry season; however, the aphids are harmless and disappear when the rains begin.
Young trees, especially Leucaena may be eaten by free-roaming animals if access is possible. Protection may be necessary in some areas. It will be too expensive for a smallholder to put wire fencing around a field, but thorn bushes or similar "unfriendly" materials can be planted or cut to provide a barrier. Where the forage trees are planted more densely, as in an intensive feed garden (see Unit 4), less fencing material will be required.
Using hired labor to weed an alley farm can pose problems, because the laborers are usually not familiar with the tree seedlings, and may think they are weeds. Farmers using hired labor should themselves weed strips along the tree rows before contracting out the rest of the field for weeding, or they should supervise the work carefully.
Tree seedlings, especially those of Leucaena grow slowly at first, and thus need attention and care during the early establishment phase. Farmers should not plant trees on land earmarked for fallow in the next year, or leave them unmanaged.
Weeds pose a great challenge to the young tree seedlings, especially in the first months of growth. Strips of land on which tree rows will be established must be weeded thoroughly before planting and kept weed-free during the first 3 months of growth.
It is easier to establish trees on a food-crop farm if the crops are planted in rows. The rows must run across the slope so that the trees effectively check erosion.
Trees should not be planted in shaded conditions, such as in mature stands of cassava, or with creeping crops such as melon. If yam is an intercrop, staking of the yams will be needed, especially near the tree rows. Late planting, especially of Leucaena can result in poor seedling development.
Hedgerows should not be thinned because this would curtail biomass production. Certain earlier works on alley farm establishment recommended thinning; however, this is unnecessary, as hedgerow density is self-regulating.
Although the hedgerows can be established with a number of companion crops, short-duration and short-statured crops have been found to be more compatible.
3.3.1 Pruning Regimes
3.3.2 Application of Mulch and Fertilizer
3.3.3 Short Fallow Periods
3.3.4 Weed Control
In an alley farming system, the crops grown between hedgerows are managed in essentially the normal way. For example, the introduction of hedgerows in a smallholders maize cropping system would not require changes in the normal practices for maize planting and maize harvesting. The major management issues which do arise in an alley farming system are:
· pruning regime (when and how to prune),
· application of mulch (how to apply mulch and expected contributions of hedgerow prunings to crops),
· fertilization (whether or not external fertilizer is needed),
· fallows (if and when to incorporate short fallow periods), and
· weed control.
Once established, the hedgerows will need to be pruned occasionally. Pruning serves two purposes: it minimizes shading of the companion crop, and it makes leaves and branches available, e.g., for mulching, staking, and firewood. Hedgerow pruning is a pivotal activity in alley farming. It is the most labor- and management-intensive component of the system.
A pruning regime refers to the type and frequency of pruning practiced at a site. The choice of pruning regime depends on several factors, including the crop and hedgerow species, the relative importance and type of products, by-products, and services expected from the hedgerows, and the amount and timing of labor available for hedgerow management and harvesting. The optimal pruning regime choice will often be a compromise between keeping the woody plant in good condition for long-term production, providing adequate mulch (and stakes, etc.) for the farm, and avoiding short-term damage to the companion crops.
Pruning Techniques
There are two types of pruning techniques, as illustrated in Figures 3-4, 3-5 and 3-6. In coppicing, the preferred technique in most cases, the trees are cut close to the ground - at a height of 30 to 60 cm. New shoots will be produced from the stump. In pollarding, the crown of a tree is cut back to a height of roughly 2 meters. Regrowth will be beyond the reach of browsing animals. Pollarding is sometimes preferred by farmers. However, coppicing at roughly 60 cm is usually best, because if the stumps are any taller, the regrowth may give too much shade to companion crops. Recent experience in East Africa suggests that, where shading competition is not a problem, a coppicing height of 1 meter may be advantageous because it minimizes workers' back strain. If stumps are shorter than 30-60 cm, tree productivity is reduced.
Figure 3-4. Leucaena leucocephala and most other alley farming species should be coppiced at a height of 30-60 centimeters.
Figure 3-5. Coppicing with a Swede saw. The trees have been pruned many times previously.
Figure 3-6. Pollarding involves the removal of the tree's crown, leaving a main stem of about 2 meters.
For manual pruning, a sharp cutlass or slasher should be used. A blunt cutlass or slasher that splits up the stem and strips the bark may predispose the trees to disease and delay regrowth; this can result in the death of the trees. Mechanized pruning could be used to save labor. For pruning large plots, cutting back one hectare of 1-year old Leucaena hedgerows (spaced 4 m apart) using Howard rotary blades takes about one hour. Small 2.5-horsepower backpack brush cutters have also given satisfactory results for pruning uniformly sized plants with a diameter of less than 3 cm. It takes about 8 hours to prune one hectare with brush cutters.
Pruning Schedules
A prototypical pruning schedule is shown in Figure 3-7. Leucaena is planted with maize at the start of the first growing season. The maize is harvested at the end of the first season, but the Leucaena is allowed to grow continuously for a full year. As the second year's maize crop is established, the hedgerows are coppiced to just above knee height (approx. 60 cm), and the prunings are used as mulch. The average height at one year is Usually in the range of 2.0 to 2.5 m, but is dependent on environmental conditions.
Regrowth in the second and subsequent years is rapid. The new shoots will need to be pruned to prevent excessive shading of the maize growing in the alleys. For Leucaena the new shoots should be at least 1 m long before the next cutting. In the humid zone, on non-acid soils, shoots usually reach 1m in about 6 weeks during the rainy season and 8 to 12 weeks in the dry season. Thus, the farmer will need to cut back the hedgerows once or twice as the maize matures (as shown in Figure 3-7).
If a second-season crop will be grown, such as cowpea, the hedgerows should be coppiced again at the start of the second season. The prunings can be applied as mulch for the cowpeas. Hedgerows should be pruned as necessary to prevent excess shading - perhaps once or twice during the second cropping season. In the dry season, hedgerows can be left unpruned for continuous growth (as in Figure 3-7). Or, if the hedgerows are used for livestock fodder, they may be pruned when new shoots are of suitable length.
Table 3-4. Recommended pruning frequencies of Leucaena hedgerows spaced 4 meters apart. Greater pruning height requires more frequent pruning to prevent shading of adjacent crops.
|
Pruning Height |
Maize |
Cowpea |
|
25 cm |
2 prunings |
1 pruning |
|
75 cm |
3 prunings |
2 prunings |
Figure 3-7. Schedule for establishing and managing a prototypical alley farm.
From the Leucaena/maize/cowpea prototype schedule, we may extract the following generally applicable principles of hedgerow pruning:
· When the hedgerow is established, pruning should be avoided for the first 6-12 months. In semi-arid areas, pruning should be delayed for 12-18 months after planting, or even longer.· At the time of planting food crops in an established alley farm, the trees should be coppiced to provide mulch and fertilizer for the crop and also to avoid shading crop seedlings.
· Regrowth after this initial cutting may be harvested selectively and continuously for feeding livestock, or it may be pruned periodically to be used as additional mulch for soil fertility maintenance and to avoid shading.
· As a general rule, the lower the hedgerows and the taller the crop, the less frequently is pruning needed (Table 3-4). Frequent pruning favors leaf biomass over wood yield.
· The second year pruning schedule can be repeated in the third and subsequent years of alley farming. In total, the hedgerows will be pruned 4 to 6 times per year.
These principles may be applied, for example, to farms where two or more food crops are grown simultaneously in the alleys. Figure 3-8 illustrates the schedule for alley farming with maize and cassava.
In mulching, hedgerow prunings are distributed on the soil surface in the alley before planting and while crops are growing. The potential benefits of applying the pruning as mulch to companion crops are reviewed in Unit 1. One crucial benefit is the fertilization effect of the mulch. For example, Leucaena and Gliricidia hedgerow prunings contribute about 40 kg of N per hectare to the companion crop (as reviewed in Unit 1).
Prunings from Leucaena are a more effective source of nitrogen when incorporated into the soil than when applied as mulch. This is because prunings decompose at a faster rate in the soil. When buried in the soil, fresh Leucaena prunings have a half-life of less than 10 days.
Figure 3-8. Cropping sequence diagram for establishing Leucaena leucocephala hedgerows for alley farming with maize/cassava.
Crops typically use N from prunings at low rates of efficiency (18-36%), probably due to lack of synchronization between crop demand and N supply, and because of losses of N through volatilization and leaching. Small amounts of supplementary N fertilizer may be needed to realize maximum yield of the alley-farmed maize. Research has shown that the presence of mulch tends to increase the effectiveness of fertilizer application.
As a general rule, optimum long-term management of an alley farm will include occasional applications of prudent amounts of fertilizer. For most environments, the idea that alley farming eliminates all external requirements for fertilizer is a misconception. For farmers who cannot afford either fertilizer or long fallows, alley farming can be a valuable management option for sustaining and/or intensifying production. However, farmers who can afford external inputs of fertilizer (whether inorganic fertilizers, animal manure, etc.,) will be able to obtain better results. For these farmers, the optimum strategy for managing an alley farm will include inputs of external fertilizer and/or short fallow periods (see below).
Alley farming allows long periods of continuous cultivation on one plot. For low-input agriculture in areas where long fallow periods have become a luxury, alley farming provides clear benefits over traditional systems. Yet the question arises: should an established alley farm be cropped indefinitely? Recent research shows that this is probably not the optimum management practice.
Farmers who can afford an occasional fallow will enhance the sustainability of the alley farming system through the integration of short fallows into the farming cycle. No crops are grown for two years, and small ruminants may be allowed to graze. Such fallows show positive effects on survival, growth, vigor, and productivity of hedgerows, and on their soil fertility maintenance and regeneration abilities. These benefits have been demonstrated on both acid and non-acid soils.
For example, a long-term alley farming and grazing trial with L. leucocephala compared a continuous alley farming system with a rotational system of alley farming and a short (2-year) grazing fallow. After the fallow period, the rotation system yielded about 35% and 55% more maize than the continuously alley farmed system and the control plot (no trees), respectively. The rotation system showed higher yields for at least three years after the fallow.
Short fallow periods in alley farming also allow the satisfaction of farmer requirements for stakes, wood, and fodder. Moreover, they are effective in combating noxious and problem weeds such as Imperata cylindrica and Chromolaena odoratum.
An example of a rotation system of 8 years' alley farming to 2 years' fallow is illustrated in Figure 3-9. The fallow may be left completely unmanaged. Alternatively, the following management practices could be used during the fallow period:
· Pruning of hedgerows and application of prunings as mulch (for soil improvement and weed suppression).· Infrequent pruning to provide firewood and stakes.
· Pruning after the rainy season to prevent leaf drop in species such as Gliricidia. This will maximize dry season availability of foliage.
· Grazing by small ruminants or cattle (for fodder and soil improvement).
· Occasional weeding, especially if volunteer Leucaena seedlings pose a weed problem.
Figure 3-9. Rotation of 8 years' alley farming and 2 years' fallow. Integration of short fallows can improve the sustainability of the system.
Alley farming can aid in the suppression of weeds by providing mulch cover and by shading the plot during the dry season. Prunings from slow-decomposing MPT species, such as Acioa barteri and Alchornea cordifolia, can suppress weed growth if applied in sufficient quantity. There is evidence that, as alley farming enriches the soil, food crops are better able to compete with problem weeds such as Imperata grass. Weed suppression can be a significant benefit of alley farming, especially in small-scale farming systems, where weeding can account for over 30% of labor used in crop production.
Moreover, alley farming provides a means to recover cropland that has been taken over by problem weeds. If the hedgerows are allowed to grow for two years and close their canopies, most troublesome weeds will be shaded out. Gliricidia sepium and Acioa barteri have proven particularly effective in this regard. Weed research in alley farming is a new field, however, and there is little information on how or when alley farming systems suppress weeds. The key parameters for monitoring weeds are weed density, species composition, seed bank analysis, and weed dry weight.
Some MPT species have the unfortunate characteristic of producing large quantities of seeds. Leucaena for example, can pose a major weed problem during fallow periods. Volunteer Leucaena seedlings need to be controlled early before they develop an extensive root system.
All answers can be found in the text and figures of Unit 3.
1. Name three key technical factors for obtaining the full benefits of alley farming systems:
1. ________________________
2. ________________________
3. ________________________
2. The following statements concern recommended practices for establishing hedgerows. Circle T for true statements or F for false ones:
|
i) The trees should be planted at the end of the major rainy season. |
T |
F |
|
ii) Trees and shrubs must be planted by machine. |
T |
F |
|
iii) Leucaena may be planted in the same row with maize. |
T |
F |
|
iv) Deep seed placement hampers germination and emergence. |
T |
F |
|
v) Pretreatment of legume seeds with acid is the preferred method of scarification in all cases. |
T |
F |
|
vi) Inoculation is a technique for preventing tree diseases. |
T |
F |
|
vii) If a legume tree species was grown successfully in a plot in the previous year, replanting of the same species may not require inoculation with rhizobia. |
T |
F |
|
vii) Planting with seedlings requires establishment of a nursery and facilities for transporting seedlings to the field. |
T |
F |
3. For smallholder alley farming in the humid zone, the recommended spacing between hedgerows is 4-6 meters. Complete the table below by indicating whether the various environments require alleys that are wider or narrower than 4-6 meters.
|
Environment |
Alley Width |
|
|
(Compared to Smallholder/Humid Zone) |
|
i) Tractorized operations |
Wider |
|
ii) Perhumid zone |
__________________ |
|
iii) Subhumid zone |
__________________ |
|
iv) Semi-arid zone |
__________________ |
|
v) Steep slopes in humid zone |
__________________ |
4. Provide brief answers to the following questions:
i) The rationale for alley cropping in the semi-arid zone differs from that in the humid zone. Explain.ii) Farmers observe that their Gliricidia hedgerows have become infested with aphids, and that their Leucaena hedgerows are being attacked by termites. Which of these problems is potentially serious, and which one can most likely be ignored?
iii) Why is coppicing preferable to pollarding as a pruning technique?
iv) What is meant by the term "pruning regime"?
5. Imagine you are setting up an alley farm using Leucaena. Assume you will be planting maize during the first season (May-Aug), cowpeas during the second (Sept-Dec), and no food crop during the dry season (Jan-April). Assume also that at each pruning you will cut back the trees to a height of 25 cm. Use the calendar below to plan the necessary establishment and management activities, paying special attention to the scheduling of tree prunings. There is more than one possible "correct" calendar.
Use these codes:
PM = Plant maize
PL = Plant Leucaena
PC = Plant cowpea
HM = Harvest maize
Pr = Prune Leucaena
HC = Harvest cowpea
W = Weed plot
|
Yr. 1 |
|
|
|
|
|
|
|
|
|
|
|
|
|
|
J |
F |
M |
A |
M |
J |
J |
A |
S |
O |
N |
D |
|
Yr. 2 |
|
|
|
|
|
|
|
|
|
|
|
|
|
|
J |
F |
M |
A |
M |
J |
J |
A |
S |
O |
N |
D |
|
Yr. 3 |
|
|
|
|
|
|
|
|
|
|
|
|
|
|
J |
F |
M |
A |
M |
J |
J |
A |
S |
O |
N |
D |
6. If optimum long-term performance of a plot is desired, alley farming in most environments will reduce but not eliminate the need for (a) fertilizer and (b) fallow periods. Explain.
_______________________________________________________
_______________________________________________________
_______________________________________________________
_______________________________________________________
_______________________________________________________
7. Describe two ways in which alley farming contributes to weed suppression.
1. _____________________________________________________
_______________________________________________________
2. _____________________________________________________
_______________________________________________________
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