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Unit 1: Introduction to Alley Farming

Main contributor: B.T. Kang


1.0 Performance objectives
1.1 The rationale for alley farming in tropical Africa
1.2 Description of alley farming
1.3 History of alley farming research
1.4 Review of recent research
1.5 Research needs
1.6 The alley farming network for tropical Africa
1.7 Feedback exercises
1.8 Suggested reading
1.9 References


1.0 Performance objectives

Unit 1 is intended to enable you to:

1. Discuss the importance of alley farming in sub-Saharan Africa in the context of declining agricultural productivity in the region.

2. Discuss the potential of agroforestry technologies for addressing the ecological and economic constraints of small-scale farming.

3. Describe the essential characteristics of an alley farming system.

4. Compare and contrast alley farming with the bush-fallow system.

5. List major benefits of alley farming.

6. Recall major stages in the development of the alley farming concept in tropics.

7. Demonstrate your familiarity with recent research concerning alley farming's effects on soil properties and crop production.

8. Describe the priority areas for applied and basic research in alley farming.

9. Explain the functions and strategy of the Alley Farming Network for Tropical Africa (AFNETA).

1.1 The rationale for alley farming in tropical Africa


1.1.1 Africa's Agricultural and Environmental Crisis
1.1.2 Bush-Fallow Systems no longer Viable
1.1.3 The Potential of Agroforestry


Alley farming integrates modern science with the art and wisdom of traditional bush-fallow cultivation (slash-and-burn agriculture). Alley farming is a low-input system that has great potential for increasing food production in the humid and subhumid tropics. Its methods are more intensive and productive than the cyclic cropping practices which characterize Africa's traditional farming systems. At the same time, alley farming provides a way to sustain agricultural production in the face of rising land pressure and worsening soil degradation.

1.1.1 Africa's Agricultural and Environmental Crisis

Much of the uplands in the humid and subhumid tropics is used for traditional shifting cultivation farming. This is particularly the case in sub-Saharan Africa, which is dominated by low activity clays soils that are less suitable for conventional mechanized and high-chemical-input farming. Such traditional farming, because of rapidly increasing human population and subsequent land use pressure, cannot feasibly be practiced on a sustainable basis. Conversely, capital-intensive agricultural technologies, though agronomically feasible in selected areas, are not affordable for the small-scale family farmers who comprise the majority of the agricultural population in tropical Africa. Farmers are faced with progressively degrading soil, decreasing crop yields, and limited access to commercial inputs. There is an urgent need to provide them with technologies that have significant returns and long-term sustainability.

During the past two decades sub-Saharan Africa has witnessed a steady decline in its agricultural productive capacity (Figure 1-1). The cumulative result is that the region, which in the 1950s and 1960s was virtually self sufficient in food, has become a net importer of food. In 1985 twenty percent of Africans depended for their food supplies on food imports and food aids.

Figure 1-1. Per-capita food production in sub-Saharan Africa declined steadily during the 1970s and early 1980s. This alarming trend stimulated investigations into the suitability of alley farming in tropical Africa.

(Source: data from US Dept of Agriculture, as adopted in World Bank (1984) Toward Sustainable Development in Sub-Saharan Africa)

This agrarian decline coincides with increasing environmental degradation. The land use patterns associated with traditional cultivation systems are extensive (rather than intensive), and disturb more land than actually required for farming. In many areas, the current high rate of population growth and the resultant land pressure have sharply reduced restorative fallow periods. The land is no longer allowed to rest adequately. These factors, in combination with inappropriate "modern" farming methods, have resulted in increased rates of deforestation, soil erosion, and land degradation. It has been estimated that tropical Africa is losing annually more than 3.7 million hectares of forest cover. Of this, almost 70 percent is due to shifting cultivation involving clearing of forest in the humid zone or patches of grasses and trees in the subhumid zone.

The practice of repeated and frequent burning in the traditional systems further adds to the problem of land degradation. There is considerable evidence that repeated flash burning of vegetation causes increased "grassification". Since, in the majority of cases in the humid and sub-humid tropics, the grasses are less effective in soil rejuvenation than the original vegetation, land degradation is a common phenomenon. The degradation of land is one of the most alarming features of the African food and environmental crisis.

1.1.2 Bush-Fallow Systems no longer Viable


1.2.1 Essential Characteristics of the System
1.2.2 Comparison to Bush-Fallow System
1.2.3 Summary of Benefits


In many parts of the humid and sub-humid tropics, particularly in Africa, the dominant food crop production pattern is the bush-fallow system, also called shifting cultivation or "slash-and-burn". In this system, short cropping periods (1-3 years) alternate with long fallow periods (6 or more years).

The restorative power of fallows is linked to the regrowth of deep rooted trees and shrubs that recycle plant nutrients and build up soil organic matter (Figure 1-2). During the fallow period, plant cover and leaf litter protect the soil from the impact of high intensity rain, and roots help to bind the soil, increase water infiltration, and reduce run-off and soil erosion. In addition, the mulch and the shade provided by tree and shrub canopies reduce soil temperature and maintain soil moisture conditions that are favorable for beneficial soil organisms. Shading also reduces weeds.

As well as restoring soil fertility, the bush-fallow system provides food, livestock feed, staking and building materials, firewood, and herbal medicines. Where land is abundant, the bush fallow system has proved to be a stable and efficient method for restoring soil productivity. Food crops grow well on newly cleared land after a long rest period.

Figure 1-2. Theoretical relationship between length of fallow and soil productivity (Guillemin, 1956). When fallow periods are shortened beyond a restorative threshold point, soil fertility and productivity decline. (Aaron. Trop. II, 143-176)

The efficiency of shifting cultivation depends on two related factors: (1) the duration of the fallow period, and (2) the nature and density of the fallow vegetation. Rapid increases in human population and the associated increases in demand for farmland and wood products have over-stretched this traditional system. Long fallow periods, which in the past lasted 10-25 years, have been shortened drastically or have disappeared in most areas of Africa. This has resulted in increasing degradation of farmland, increasing infestation by problem weeds, and declining food crop yields. Fertilizer use has not been a viable option in much of the tropics, because of its high cost and unavailability to most smallholder farmers, especially those in sub-Saharan Africa. Even where such inorganic fertilizers are available, continued use of high rates of N fertilizer may lead to soil acidity problems.

The loss of soil fertility proceeds rapidly, because the nature of much of Africa's soils is such that over-exposure and over-cultivation can easily lead to their degradation. Agricultural land in the humid and sub-humid tropics is dominated by low activity clays (LAC) soils. The inherent characteristics and limitations of LAC soils make the large upland areas which they dominate less suitable for conventional mechanized and high-chemical-input farming methods. These soils have inherently low fertility, and are highly erodible when left unprotected.

1.1.3 The Potential of Agroforestry

It is widely recognized that the biggest challenge facing agricultural research in the tropics is the development of farming systems capable of ensuring increased and sustained productivity with minimum degradation of the soil resource base. Reversing the trend of declining per-capita food production in sub-Saharan Africa, therefore, does not depend solely on the development of improved and high-yielding crop varieties. Development of sustainable production systems is necessary to foster and maintain advantages derived from such improved varieties. Systems are needed that incorporate the biological stability and nutrient balance characteristic of the traditional shifting cultivation system, while allowing intensification of production over the long-term.

Africa's agricultural predicament presents a two-fold challenge for agricultural research:

· to increase the productivity and income of small-scale, resource-poor African farmers
· to provide such farmers with appropriate technologies and systems that will enable them to intensify their production.

What type and level of technologies and systems are needed? This is a big question. According to the U.S. Office of Technology Assessment (1988), desirable technologies should meet four criteria. They should be:

· technically and environmentally sound,
· socially desirable,
· economically affordable, and
· ecologically sustainable.

Figure 1-3. Agroforestry systems under various spatial arrangements. Alley farming is one type of agroforestry:

Trees along borders of crop fields

Alternate strips or alley cropping

Alternate rows

Random mixture

During the past two decades there has been an increasing interest in using the agroforestry approach for developing more productive, low-input, and sustainable land use technologies. Agroforestry technologies frequently meet all four of the above criteria. Agroforestry is an integration of a tree component into an agricultural production and land use system (Figure 1-3). Such systems have been widely acclaimed as a solution to tree depletion, soil degradation, and declining yields under shifting cultivation. Agroforestry is a sustainable land management system which increases the overall yield of the land. It combines, simultaneously or sequentially, the production of trees and the production of crops and/or animals on the same unit of land, and it applies management practices that are compatible with the cultural practices of the local population.

In the tropics, trees have long been recognized as essential both for the stability of the environment and for maintenance of soil fertility for crop production. Trees have been recognized as major elements in soil fertility regeneration and conservation, as reflected by their prominence in traditional farming systems. One agroforestry system that has received a good deal of research attention and has shown great promise for sustainability is alley farming.

Figure 1-4. A newly planted alley farming plot. Hedgerows of multipurpose trees are planted at 4-6 meter intervals for humid or sub-humid zones. Food or fodder crops are planted in the "alleys" between. This farmer produces his own fertilizer.

1.2 Description of alley farming

1.2.1 Essential Characteristics of the System

Alley farming is an agroforestry system in which food or forage crops are grown in the "alleys" between hedgerows of trees or shrubs. The trees or shrubs - preferably fast-growing, leguminous (nitrogen-fixing) species - are established in hedgerows usually spaced 4-8 meters apart. The trees are periodically pruned and managed during the cropping phase to prevent shading of the companion crops. The prunings of foliage and young stems are incorporated into the soil as green manure or used as mulch. Some portion of the tree foliage can be harvested and fed to livestock, particularly small ruminants. Alley farming is a scale-neutral system; though initially developed for smallholders, it can also be adapted for mechanized large-scale farming. The system has been tested successfully with the use of appropriate woody species and crop combinations under on-farm conditions in West, Central, and East Africa.

Alley farming goes by different names in certain publications and regions. The International Council for Research in Agroforestry (ICRAF) calls the system "hedgerow intercropping". In Sri Lanka, it is called "avenue cropping". Some authors call it "contour hedgerow farming". Similar farming approaches have been tried with success in other parts of the tropics such as the Leucaena contour terracing system in eastern Indonesia and the sloping agricultural land technology (SALT) in the southern Philippines. Certain authors make a distinction between "alley farming" (livestock component included) and "alley cropping" (no livestock component). In this manual, such a distinction is not used.

Figure 1-5. Alley farming with bananas and Leucaena. The hedgerows allow more intensive banana production by providing mulch, poles, and shading of young plants.

1.2.2 Comparison to Bush-Fallow System

Alley farming is designed to be a sustainable alternative to traditional bush-fallow systems (shifting cultivation). It is a low-input, improved bush-fallow system that can be sustained even under conditions of land scarcity. As a substitute for traditional slash-and-burn systems, it offers the opportunity to reduce deforestation and land degradation.

The woody hedgerow component of the alley farming system retains the basic features of the bush-fallow for soil protection, nutrient recycling, weed suppression, and for provision of browse, staking material, and firewood. Alley farming parallels bush-fallow systems in the sense that tree foliage is used to maintain and improve soil fertility. However, land-use efficiency is higher because cropping and fallow are carried out on the same plot of land, at the same time.

Figure 1-6. Stages in the evolution of managed fallows and multistory agroforestry in the humid tropics. Stages I, II, and III represent traditional bush-fallow systems. Alley farming techniques may be incorporated in stages IV, V, and VI.

Stage I. Low management intensity. Attention to crop only.

Stage II. Increased management intensity. Shorter fallow period. Decreasing return to labor. Awareness of fallow contribution. Observation of species in the fallow.

Stage III. Increased management intensity in cropping period. Low-level intervention in fallow. e.g. Encouraging dominance of selected species.

Stage IV. Both crop and fallow intensively managed. Fallow planted and protected. Fallow period shorter than cropping period.

Stage V. Intensively managed continuous cropping. Trees intercropped with annual foods.

Stage VI. Intensively managed trees and crops in multistory or agroforestry complex.

As an improved system, alley farming has various advantages over the bush fallow system, but also requires more labor and management inputs, as shown in Table 1-1. Alley farming may be most attractive in places where farmers feel a need to intensify crop production but face soil fertility and/or soil erosion problems. This situation is often characteristic of densely populated areas, but may also occur wherever some farmers wish, or are forced, to increase production on a plot of limited size.

Table 1-1. Differences in management of traditional bush fallow and alley farming systems (Source: Kang et al., 1989).

Traditional Bush-Fallow

Alley Farming

· Mixed native woody species retained

· Woody species selected, preferably fast-growing legume species

· Irregular planting pattern

· Hedgerow pattern

· Before cropping, trees and shrubs are cut back and burnt to release nutrients

· Trees and shrubs are periodically pruned, with prunings used as mulch and green manure

· Fire used for controlling growth

· Periodic prunings control hedgerow growth

· Short-term cropping allowed

· Continuous cropping allowed

1.2.3 Summary of Benefits

Alley farming shows great promise as a sustainable production system. An alley farming system has the potential to provide the following major benefits:

· allows a longer cropping period, more intensive cropping, and higher crop yields,
· regenerates soil fertility rapidly and effectively,
· reduces requirements for external inputs of fertilizer.

Figure 1-7. A schematic representation of the benefits of nutrient cycling and erosion control in an alley farming system (Kang et al., 1989).

Figure 1-8. Formation of natural terrace across the slope after 3 years of continuous alley farming management (After Picardo, 1984).

Obtaining the full benefits of the system depends on an appropriate design, successful hedgerow establishment, and efficient management. Fertility regeneration and other key benefits depend on the use of appropriate multipurpose trees species in the hedgerows.

The hedgerows in the system can offer some or ail of the following benefits:

· provide green manure and mulch for companion crops,
· provide biologically fixed nitrogen for companion crops,
· improve soil conservation,
· create favorable conditions for beneficial soil organisms,
· provide high-protein fodder for livestock,
· provide staking material and/or firewood.

If portions of the hedgerow prunings are fed to livestock, this will reduce the quantity available for fertilization purposes.

1.3 History of alley farming research

Some aspects of the alley farming system have been used for generations by traditional farmers at Mbaise in southeastern Nigeria. In this production system on highly acid Ultisols, farmers plant Acioa barteri hedgerows for nutrient cycling, weed suppression, browse, and especially for staking material. The Acioa barteri hedgerows are pruned and burned before a short cropping cycle of 1-2 years. They are again pruned before starting the next cycle.

As far back as the early 1920s, Nalaad farmers in the Philippines were practicing a basic form of alley farming, using the leguminous tree Leucaena leucocephala to terrace steep slopes and provided green manure for crops. In the 1930s, the Dutch colonial government introduced the same technology on contour terraces on the island of Timor in eastern Indonesia, planting Leucaena hedgerows three meters apart to control erosion and improve soil fertility. The first published research on alley farming, by Hernandez in 1961 (cited in Benge, 1987), reported on four years of continuous intercropping of maize with Leucaena in the Philippines. The trees were planted on sloping land in hedgerows one meter apart and pruned bimonthly. Hernandez, (cited in Benge, 1987), reported that erosion was reduced and maize yields substantially increased.

At the International Institute of Tropical Agriculture (IITA), research on the use of woody species in food crop production systems started during the 1970s. Investigations initially involved the introduction and evaluation of species such as Leucaena and Cajanus. In 1976, the first alley farming trial was established in order to assess the potential of intercropping woody species with food crops as a land use system for managing fragile uplands dominated by low activity clays. The experiment was set up on a low fertility sandy soil (Psammentic ustorthent) using direct seeded Leucaena hedgerows.

The encouraging results of this trial created a great interest in research on alley cropping systems (Kang et al., 1981). IITA's alley-system research has been conducted primarily on the institute's headquarters farm at Ibadan, Nigeria, in the subhumid/humid transition zone, with a total annual rainfall of about 1200 mm. Research on a smaller scale is conducted on acid soils at the Onne substation, which has an annual rainfall of about 2400 mm. In some 150 on-station experiments, involving more than 10 hedgerow species, IITA scientists have focused mainly on two issues: the enhancement of soil fertility, and the establishment and management of hedgerow species.

The main research thrust has been development of the technology for use by Africa's resource-poor smallholders. However, IITA's limited experimentation with tractorized operations suggests that alley farming can be adapted to large-scale enterprises (Figure 1-9).

In the 1980s, IITA placed increasing emphasis on on-farm trials designed to develop and evaluate techniques suitable for small-scale alley farming. During the two crop years 1987-1989, collaborating farmers planted more than 80 alley experiments on their farms in the subhumid and transitional zones of Nigeria. Researchers collaborating with IITA in other countries in West and Central Africa have established similar trials on farmers' fields.

Realizing the potential of leguminous hedgerows in particular as a source of browse for livestock, the International Livestock Centre for Africa (ILCA) has expanded the alley farming concept to include livestock production. By using a portion of the foliage for animal feed in a cut-and-carry system, ILCA scientists have developed a new package which has potential benefits for both crops and animals (Okali and Sumberg, 1985).

Figure 1-9. Mechanized alley farming using Gliricidia sepium. Alley farming is scale-neutral, and can be adapted to large farms such as this.

In East and Southern Africa, national research institutions began to conduct their own alley farming experiments during the 1980s in countries such as Rwanda, Kenya, and Zambia. The Nairobi-based International Centre for Research in Agroforestry (ICRAF), with its extensive experience with multipurpose trees, has played a leading role in encouraging alley farming and related agroforestry research in these regions.

Currently alley farming techniques and similar approaches are being researched and tested, or are already used in farmers fields, in various parts of the humid tropics, as shown in Figure 1-10. Outside Africa, particularly important work is being done in Haiti, Sri Lanka, Indonesia, and the Philippines.

1.4 Review of recent research

This section reviews the results of recent research that has demonstrated alley farming's beneficial effects on soil properties, crop production, and livestock nutrition. Most of the investigations were conducted at sites in Nigeria by the International Institute of Tropical Agriculture (IITA) or the International Livestock Centre for Africa (ILCA) Humid Zone Program.

Figure 1.10 Distribution of alley farming activities world-wide. Large circle represent major centers of research.

1.4.1 Effects on Soil Properties


1.4.1 Effects on Soil Properties
1.4.2 Effects on Crop Production
1.4.3 Supplemental Nutrition for Livestock
1.4.4 Wood Production


In alley farming, prunings from the leguminous trees are used as green manure and mulch for maintaining soil fertility. With proper management, hedgerow prunings of some species can produce a large amount of biomass and nutrient yield, as illustrated in Table 1-2.

Table 1-2. Biomass and nutrient yields of woody species from five prunings of hedgerows grown on an Alfisol at Ibadan, south-western Nigeria. Inter-hedgerow spacing was 4m (B.T. Kang, unpublished).

Species

Dry matter* (t/ha/yr)

Nutrient Yield

N

P

K

Ca

Mg

(kg/ha/yr)

Acioa barteri

3.0

41

4

20

15

5

Alchornea cordifolia

4.0

85

6

48

42

8

Gliricidia Sepium

5.5

169

11

149

66

17

Leucaena leucocephala

7.4

247

19

185

98

16

* Wood harvest not included

Repeated addition of prunings in the alleys plays an important role in maintaining high soil organic matter and nutrient status. A recent study measured the long-term effects of the addition of Leucaena and Gliricidia prunings on soil properties and crop yield (Kang and Ghuman, 1989). As compared to a tree-less control plot, the alley farming plots recorded 80% higher soil organic matter after six years of cropping (Table 1- 3). Although Leucaena and Gliricidia prunings have short half- lives of 2-3 weeks, their continuous addition in large quantities has been found effective in maintaining high soil organic matter levels. (A half-life is the time required for half of a substance to decompose. One half of the prunings remain after 2-3 weeks, one quarter after 4-6 weeks, etc.)

Table 1-3. Effects of 6 years of alley farming on properties of surface soil, run off, soil loss and maize yield on an Alfisol with 7% slope (Kang and Ghuman, 1989).

Treatment

Acidity H2O (pH)

Organic Carbon (%)

Runoff** (mm) (% of rainfall)

Soil loss** (t/ha)

Maize*** yield (t/ha)

Control (no hedgerows)







Tilled

5.3

0.5

66.0(9.4)

6.18

2.3


No-till

5.4

0.9

5.6(0.8)

0.43

2.4

Alley farmed and tilled*







2 m-Gliricidia

5.2

0.8

4.8(0.7)

0.57

3.2


4 m-Gliricidia

5.1

0.8

23.1(33)

1.44

2.8


2 m-Leucaena

5.1

0.9

2.6(0.4)

0.17

3.5


4 m-Leucaena

5.1

1.1

10.7(1.5)

0.82

3.1

* Inter-hedgerow spacing: 2 and 4 m.
** Measured during first season (March-July 1988). Total amount of rainfall - 704.2 mm.
*** Fertilizer

Mulching is known to have favourable effects on physical soil properties (Lal, 1974). The presence of an adequate amount of mulch cover alleviates the negative effects of continuous cropping in many ways (Table 1-4).

Table 1-4. The beneficial effects of mulch cover on soil properties.

Mulch cover helps to:

· Maintain high soil nutrient status and high biological activity
· Reduce Al and Mn toxicity derived from soil acidification
· Protect the soil against high temperature, impact of high intensity rains, soil erosion and run off
· Prevent the breakdown of soil structure and resultant soil compaction and increase soil permeability
· Increase soil moisture retention

In alley farming, addition of Leucaena prunings has been shown to increase soil moisture retention (Kang et al., 1985). The mulching effect combined with the barrier effect of the hedgerows brings about a marked reduction in runoff and soil erosion on sloping land. Leucaena, which forms more dense hedgerows than Gliricidia, provides better control of runoff and soil erosion.

1.4.2 Effects on Crop Production

Alley farming has been tested, with encouraging results, using a variety of crops, including cereal crops (maize, upland rice), grain legumes (cowpeas, soybeans), root and tuber crops (cassava, yam), and plantain and vegetable crops, under both monocropping and intercropping systems. In an alley farming trial on an eroded Alfisol (Oxic Paleustalf) at Ibadan, south- western Nigeria, maize yields under alley cropping with various hedgerow species were significantly higher, with or without applied nitrogen, than in the control plots which had no trees (Figure 1-11). This trial also showed that, in addition to nitrogen benefit, the generally improved soil conditions resulting from alley farming also had a positive effect on maize yield.

Figure 1-11. Grain yield of maize on eroded Alfisol (Oxic Paleustalf) at Ibadan, south-western Nigeria, as affected by alley farming with woody species (Acioa barteri, Alchornea cordifolia, Gliricidia sepium and Leucaena leucocephala). Rates of nitrogen fertilizer application are shown (kg N/ha). (B.T. Kang, unpublished data).

A very important aspect of alley farming is the sustainability of crop yields over time. Results of long-term alley farming trials, also conducted at Ibadan, have shown that by applying Leucaena prunings, even without N application, maize yields can be maintained for many years at the reasonable level of approximately 2 tons per hectare (Figure 1-12). Higher yields were obtained when the prunings were supplemented with fertilizer N. The alley farming techniques thus provide flexibility in the development of low-chemical-input production systems. Removal of some or all of the prunings from alley farming plots results in a reduction of the benefits received by the crop, though application of some inorganic N can compensate for the loss.

Figure 1-12. Grain yield of first season maize in maize-cowpea sequential cropping on a Psammentic ustorthent in alley farming with Leucaena leucocephala at Ibadan as affected by N application and prunings of hedgerows (B.T. Kang, unpublished data).

Nodulating leguminous MPTs such as Leucaena and Gliricidia produce prunings with high nitrogen (N) yield (Table 1-2). For example, when inoculated with appropriate strains of nitrogen-fixing bacteria, Leucaena fixed 70 to 135 kilograms of nitrogen per hectare in six months. The N contribution from the prunings to crop(s) has been widely studied in recent years. Despite the high N-yield obtained, N. use efficiency from prunings by the associated crop(s) is known to be low. The efficiency is affected by the contents of the prunings, the decomposition rates, the timing of application in relation to crop growth, and the placement method. Kang (1988) estimated the N contribution from Leucaena and Gliricidia hedgerows to alley-farmed maize to be about 42 kg N/ha (Table 1-5). This represents a low N-use efficiency of 18 and 33%, respectively. By comparison, Gevarra (1976) reported a higher N-use efficiency of 36% for Leucaena prunings by a maize crop. More research is needed to increase the efficiency.

Table 1-5. Nitrogen yield (kg N/ha) from hedgerow prunings during one maize cropping season, N uptake by the alley-farmed maize, and estimated N gain from hedgerows to the system (B.T. Kang, 1988).

Woody hedgerow

N yield from prunings1

N uptake by maize

Estimated N gain2

Maize grain yield (kg/ha)

Control

-

26.2

-

1632

Legumes:






Gliricidia sepium

127.8

68.6

42.4(33.1)

3349


Leucaena leucocephala

231.1

68.1

41.9(18.1)

3210

1 Not including N removed with harvested wood.
2 Figures between brackets show percentage N utilization from prunings.

Little information is available on the interactions between the hedgerows and the crops. Kang et al. (1985) have shown that on non-acid soils in the humid zone the maize crop and Leucaena hedgerows do not compete for soil moisture, as Leucaena hedgerows use soil moisture from lower depths in the profile than the crop. In the humid zone, competition between the hedgerows and the crop is mainly for light. In dry regions, careful selection of MPT species and wider spacing of hedgerows is needed, so as to minimize competition for water. On acid soils, where crop and tree roots are concentrated at the soil surface, competition for nutrients can be a problem.

In alley farming with Leucaena, maize plants grown adjacent to hedgerows show poorer performance as compared with plants grown farther away, due to the shading effect. Negative effects on crops due to shading are more probable under conditions of high soil fertility. Under low fertility, the higher nutrient contribution from the litter fall near the hedgerows more than compensates for the shading effect. Thus, under low fertility, maize plants grown adjacent to hedgerows perform better (Fayemelihin, 1986).

1.4.3 Supplemental Nutrition for Livestock

The fodder resources available on smallholder farms in Africa consist mainly of residues from subsistence crops and vegetation on fallow lands. Both of these sources of animal nutrition are highly seasonal, with quality and quantity declining as the dry season progresses. Thus, one of the major constraints to livestock production in Africa is animal nutrition, especially in the dry season. It has been observed that the nutritional problem is more severe with confined animals, as free-roaming animals can select the most nutritious part of grasses and browse. Recent research conducted by ILCA scientists has demonstrated that the leguminous trees in an alley farming system constitute a valuable means for alleviation of this problem by providing nutritious fodder that can be fed to confined animals or browsed by free-roaming animals. This subject is taken up in depth in Unit 4.

1.4.4 Wood Production

Depending on the species, prunings from the hedgerows can produce substantial quantities of wood for use as fuel or as staking material (e.g., for yam cultivation). Fully grown Leucaena and Gliricidia hedges, sequentially cropped with maize and cowpeas in the Ibadan area and periodically pruned back to a height of 75 cm, produced over 5.7 and 1.4 tons per hectare respectively of dry weight of stakes. Utilizing subsoil moisture during the four-month dry season, Leucaena and Gliricidia hedgerows grew 4.0 m and 2.5 m, respectively. When allowed to grow freely for one year, the Leucaena hedgerows reached a height of over 7.5 m and produced more than 88 tons of wood per hectare.

1.5 Research needs


1.5.1 Multipurpose Tree (MPT) Screening
1.5.2 Alley Farming Management Studies
1.5.3 Livestock Integration
1.5.4 On-Farm Research and Socio-economic Assessment
1.5.5 Basic Research Needs


As previously mentioned, alley farming is based on an age-old concept and practice, but it is a new science. Despite considerable interest in using the technique, information on its potential use and limitations remains inadequate. Further research is needed to better assess the processes and merits of the technique, to improve it further, and to fine-tune the technology for local adoption. Many applied research issues can best be tackled by Africa's national agricultural research systems (NARS).

Priority areas for research are listed below. Each area of applied research is covered in a separate unit of this Core Course, namely: MPT Screening (Unit 2), Alley Farming Management (Unit 3), Livestock Integration (Unit 4), On-Farm Research (Unit 5), and Socio-economic Assessment (Unit 6). The basic research issues listed below are not covered in this manual.

1.5.1 Multipurpose Tree (MPT) Screening

1. For every agroecological zone and sub-zone, there is the need to identify suitable MPTs that could grow vigorously and be productive when subjected to alley farming management. This type of work is highly site specific and is recommended as a starting point for sites where alley farming work has never been carried out.

2. Alley farming has so far been tried with a relatively small number of MPTs. Evaluation and testing of a wider spectrum of indigenous and exotic MPTs in alley farming is needed, particularly for acid soil conditions, the semi-arid tropics, and the tropical highlands.

3. There is a need to develop methods for producing high-quality seeds of important MPTs for alley farming.

4. There is a need for improved experimental designs for screening MPTs for use in alley farming.

1.5.2 Alley Farming Management Studies

1. Having selected suitable tree species for a particular zone or site, management studies are then conducted to fine-tune management techniques for local conditions. Typical trials in this category investigate the following:

· Problems of hedgerow establishment and management;
· Effect of inter-and intra-row spacing of MPTs on hedgerow establishment and productivity;
· Effect of hedgerow prunings of different MPT species on soil fertility and crop productivity;
· Fallow integration and management in alley farming system;
· Integration of arboreal tree stands in alley farming for pole and fuelwood production;
· Problems of crop husbandry;
· Problems of pest management and disease.

2. Since managing alley farming may require a greater input of labor than traditional bush-fallow systems, more efficient tools are needed for hedgerow management so as to increase labor productivity.

3. More efficient experimental designs are needed for conducting alley farming trials so as to reduce the need for large experimental fields.

1.5.3 Livestock Integration

1. The effect of livestock integration on crop productivity, as well as the response of livestock receiving supplementation from alley farming tree fodder, need to be determined. Both cut-and-carry fodder management and the grazing of alley farms in fallow years can have implications for soil fertility maintenance and crop yield sustainability.

Experimental topics with a livestock focus include the following:

· Screening of fodder trees and assessing the effects of their integration into the alley farming system,
· Pasture production in alley farming context (tree/grass combinations),
· Performance of livestock under nutritional supplementation from different alley hedgerow species,
· Effects on crop production, soil fertility, and livestock nutrition of utilizing different proportions of hedgerow prunings as (a) mulch or (b) livestock fodder.

1.5.4 On-Farm Research and Socio-economic Assessment

1. On-farm research and development activities need to be carried out in a broad range of agroecological and socio-economic conditions for the fine-tuning of the technology, the assessment of its productivity and efficiency relative to traditional farmer practices, and the determination of the acceptability and potential adaptability of the system.

2. Socio-economic studies are needed to better assess the costs and benefits of alley farming, both short-term and long-term.

3. As there is a slow adoption rate for alley farming on the African continent, socio-anthropological studies are required to determine constraints to adoption at the farm level and to develop suitable transfer mechanisms.

1.5.5 Basic Research Needs

1. Investigations are needed to determine the factors and processes that contribute to yield sustainability and maintenance of soil productivity. There is a need to better quantify the turnover of soil organic matter and its effect on soil properties and biotic activities.

2. Information is scarce on the spatial interface, particularly the subterranean interactions, between woody hedgerows and crops. Better information on the use of and competition for soil nutrients and water can assist in developing more productive alley farming systems.

3. Information is still scanty on the soil and nutrient requirements of MPTs with potential for alley farming. Better quantification is needed of the requirements for rhizobium inoculation, of the N2 fixation process in MPTs, and of the benefits received by crops from the nitrogen and other nutrients found in tree prunings. Similarly, the role of mycorrhizal inoculation in enhancing phosphorus nutrition to MPTs and the phosphorus contribution to crops need to be assessed.

1.6 The alley farming network for tropical Africa


1.6.1 Research Strategy


The Alley Farming Network for Tropical Africa (AFNETA) was set up to enhance cooperation between the international agricultural research centers (IARCs) and national agricultural research systems (NARS) of Africa in the area of alley farming research. Until AFNETA commenced operations in 1989, the involvement of national institutions in research on alley farming was minimal. The three international centers, IITA, ILCA, and ICRAF, are considered the founding members of AFNETA. They provide technical backstopping in the areas of library services, research, and training. The network is currently operating in twenty countries in tropical Africa (Figure 1-12).

The AFNETA/NARS collaborative research program currently involves more than 50 experiments at 32 institutions in 20 different countries (Figure 1-13). The NARS/AFNETA projects in Africa are supplemented by external projects in U.S. universities that address research issues of a basic and strategic nature. Funding is sought for an additional 30 experiments at 23 institutions.

The AFNETA/NARS projects are investigating a broad range of research issues, classified in four main categories:

1. Screening and evaluation of multipurpose tree species,
2. Alley farming management trials,
3. Integration of livestock in alley farming systems,
4. On-farm research and development, and socio-economic assessment.

1.6.1 Research Strategy

AFNETA has mapped out a research strategy for scientists and institutions interested in addressing the foregoing research issues (Sanginga, 1990). Where there has been no previous history of alley farming - as in most of the semi-arid and arid zones - there may be need for a strong on-station component initially to determine if alley farming has any potential. A typical pattern could be that tree selection and management experiments are carried out mainly on-station, with major farmer involvement occurring only when biologically sound prototypes have been developed. For countries such as Nigeria, where alley farming has already shown promise, on-farm and livestock integration experiments will be justified.

A major network goal is to test the adaptability of alley farming across the agroecological zones of tropical Africa: humid, sub-humid, semi-arid and highlands (Figure 1-14). The collaborative research program also aims to move increasingly into on-farm, adaptive research. To enable comparison of results and allow regional analysis, AFNETA requires participating researchers to use standard methods and a minimum data set.

Figure 1-13. Distribution of AFNETA's ongoing collaborative research projects in 1990-1991, by country.

Figure 1-14. The agroecological zones of tropical Africa.

It might seem scientifically sound for each AFNETA project to proceed as in Figure 1-15A: first by identifying suitable MPTs; next by incorporating these in management research; then by using the knowledge gained to design and test prototypes; and finally, when confident about their performance, by proceeding to on-farm or extension research. However, such a sequence could take over 30 years (Willey and Young, 1990). In practice, the different types of research may proceed more nearly in parallel, with a continuous transfer of knowledge from one to the other, as in Figure 1-15B. Management trials are likely to be established from the start of the program, at the same time as the MPT screening and evaluation, making use of such multipurpose trees as are believed to be suitable during the testing of prototypes. Similarly, the recommendation to extension will not be handed over at a specified time. Instead, recommendations will progressively improve as the program advances.

Figure 1-15. Alternative research strategies. AFNETA's collaborative research program employs strategy B.

1.7 Feedback exercises

All answers can be found in the text and figures of Unit 1.

1. The following five statements concern Africa's agricultural and environmental crisis. Circle T for true statements or F for false ones:

i) Low activity clays soils are rare in sub-Saharan Africa.

T

F

ii) Sub-Saharan Africa is a net importer of food.

T

F

iii) Repeated flash burning of vegetation causes ''grassification.''

T

F

iv) Per-capita food production has declined less in Africa than in Asia.

T

F

v) Population pressure on land has not yet reduced fallow periods.

T

F

2. Provide brief answers to the following questions:

i) How is soil fertility restored in bush-fallow systems?
ii) Why are many African soils susceptible to rapid declines in soil fertility?
iii) What is agroforestry, and why do agroforestry technologies show promise for low-input land use systems?
iv) Why is alley farming considered to be one type of agroforestry?

3. Fill in the blanks with the missing words or phrases.

i) Alley farming is defined as the growing of ____________ or ____________ crops in the "alleys" between rows of ____________.

ii) Hedgerows are pruned during the growing season in order to prevent and to provide ____________ for crops and/or ____________ for livestock.

iii) Land-use efficiency is higher in alley farming than in bush-fallow system because ____________ and ____________ are carried out simultaneously.

iv) Bush-fallow uses fire for controlling vegetation and allows short-term cropping. In contrast, alley farming uses ____________ for control and allows ____________ cropping.

4.

a.) List three overall benefits of alley farming:

1. ________________________
2. ________________________
3. ________________________

b.) List at least six benefits provided by the hedgerows in the system:

1. ________________________
2. ________________________
3. ________________________
4. ________________________
5. ________________________
6. ________________________

5. The following statements concern the history of alley farming research. Circle T for true statements or F for false ones:

i) Alley farming was invented by scientists at IITA.

T

F

ii) Alley farming systems have been used by generations of farmers in the Philippines and Nigeria.

T

F

iii) Scientists at ILCA pioneered the expansion of alley farming to include livestock production.

T

F

iv) Africa's national agricultural research systems were not involved in alley farming research until the AFNETA network began operations in 1989.

T

F

v) The only tree species to receive research attention so far are Leucaena leucocephala and Gliricidia sepium.

T

F

6. Provide brief answers to the following questions:

i) In recent experiments, prunings of Leucaena and Gliricidia have been shown to have positive effects on soil properties. Cite several specific examples of such effects.

ii) In general, what are the beneficial effects of mulch cover on soil properties?

iii) In IITA's long-term trials at Ibadan, what level of maize yields (in t/ha) have been maintained without application of N fertilizer? What levels have been possible there with application of N fertilizer?

iv) Alley farming systems must be managed to minimize competition between hedgerows and crops. What types of competition would be of greatest concern in a humid area? In a semi-arid area?

7. Researchers have identified four main categories of research needs for further development of alley farming technologies. List them.

1. Multipurpose Tree Screening
2. ________________________
3. ________________________
4. ________________________

8. At the time this manual was published, AFNETA's collaborative research program involved experiments in 20 countries. Name the countries in your own region of Africa (West, Central, East, or Southern) in which AFNETA experiments are located.

1.8 Suggested reading

Kang, B.T. 1991. Sustainable agroforestry systems for the tropics: concepts and examples. IITA Research Guide 26. Ibadan: IITA.

Kang, B.T., L. Reynolds, and A.N. Atta-Krah. 1990. Alley Farming. Advances in Agronomy 43:315-359. Available in IITA Reprint series.

Kang, B.T., and G.F. Wilson. 1987. The Development of Alley Cropping as a Promising Agroforestry Technology. In: H.A. Steppler and P.K.R. Nair (eds.). Agroforestry: A Decade of Development. pp 227-243. Nairobi: ICRAF. Available in IITA Reprint series.

1.9 References

Benge, M.I. 1987. "Agroforestry System" (mimeo), Bureau of Sci. Technol., U.S. Agency for International Development, Washington, DC.

Fayemelihin, A.A., 1986. Effect of alley cropping with woody legume (Leucaena leucocephala) and nitrogen application on intercropped maize (Zea mays). Training Report. Ibadan, Nigeria: IITA.

Guevarra, A.B. 1976. Ph.D. Thesis, Univ. of Hawaii, Honolulu.

Kang, B.T. 1988. Nitrogen cycling in multiple cropping systems. In: J.R. Wilson (ed.) Advances in Nitrogen Cycling in Agricultural Ecosystems: pp. 333-348. Wallingford, England: CAB. Int.

Kang, B.T., and B.S. Ghuman. 1989. Alley Cropping as a Sustainable Crop Production System. Paper read at International Workshop on Conservation Farming on Hillslopes. Taichung, Taiwan, R.O.C. March 20-29, 1989. (In press.)

Kang, B.T., N. Grimme, and T.L. Lawson. 1985. Alley cropping sequentially cropped maize and cowpea with leucaena on a sandy soil in southern Nigeria. Plant and Soil 85: 267-277.

Kang, B.T., A.C.B.M. van der Kruijs, and D.C. Couper. 1989. Alley cropping for food crop production in humid and subhumid tropics. In: B.T. Kang and L. Reynolds (eds). Alley Farming in the Humid and Sub-humid Tropics. pp. 16-26. Ottawa, Canada: IDRC.

Kang, B.T., G.F. Wilson, and T.L. Lawson. 1984. Alley Cropping: A stable alternative to shifting cultivation. Ibadan, Nigeria: IITA. 22p.

Kang, B.T., G.F. Wilson, and L. Sipkens. 1981. Alley cropping maize (Zea mays) and leucaena (Leucaena leucocephala Lam.) in southern Nigeria. Plant and Soil 63: 165-179.

Lal, R. 1974. Role of mulching techniques in tropical soil and water management. Tech. Bull. IITA, Ibadan, Nigeria.

Okali, C., and J.F. Sumberg. 1985. Sheep and goats, men and women: Household relations and small ruminant development in southwest Nigeria. Agricultural Systems 18: 39-59.

OTA (Office of Technology Assessment), 1988. Enhancing agriculture in Africa. A role for U.S. development assistance. OTA, Congress of the United States, Washington DC, USA.

Picardo, E.P., 1984. Soil erosion and ecological stability. In: E.T. Crasswell, J.V. Remenyi, and L.G. Nallana (eds). Soil Erosion Management. ACIAR, Proc. 6, Canberra: 82-85.

Sanginga, N. 1990. Summary comment on and finalization of country projects, submitted to IFAD. Unpublished AFNETA document.


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