Agroforestry

Trees used in Agroforestry

Species	Ecology	Management System	Tree management	End Use	Remarks
Grevillea robusta © P. Maundu, World Agroforestry Centre, Nairobi, Kenya	The Grevillea robusta originated from Australian and is widely used in Africa, 0 - 3000 m. It does well on neutral to acidic loam or light sandy soils but is not tolerant to waterlogging or heavy clays. Found in Ecozones II - V	The Grevillea .spp may be found in; Plantation, Hedge planting,  Agroforestry (coexisting with food-crops), Woodlot and, Shelterbelt system	The Grevillea .spp may be propagated by use of wildings or seedlings.  Pollarding, lopping, coppicing and pruning optimizes their benefits if used in their management. Note; Only young trees coppice well Maturity takes 6 yrs for poles and 30 yrs for timber	Firewood, charcoal, timber, furniture, poles, veneer, fodder (leaves low quality), bee forage,shade, ornamental, mulch, soil conservation and, windbreak	Some communities believe the species attracts lightning in homesteads. However, it is an extremely important tree in the Kenyan highlands and has become an integral part of the farming system in many areas.
Sesbania sesban	The Sesbania spp survive waterlogging and fix nitrogen improving the soil fertility. Naturally, it distributed from Senegal to Somalia and south to South Africa. It's all over tropical Africa and Asia. It tolerates acid and saline soil and is common in riverine vegetation and in Kenya, is found at the margin of fresh water lakes like Naivasha and Baringo and in seasonal swamps. Widely cultivated in western Kenya; 350- 1,900 m above sea level and Ecozones I - IV	May occur in dense stands, agroforestry (mixed farming system), conservation	The tree is very fast growing and pruning and short rotation is employed in their management. Propagation is by direct sowing at site or wilding and it takes 2 to 3 years to reach maturity.	Firewood, poles, medicine (leaves and roots), fodder, shade,soil enrichment via nitrogen fixation,soil conservation (improved fallows), fibre, veterinary medicine and, soap (leaves)	The species harbours rootknot nematodes and should therefore be avoided in combination with crops that are very sensitive to nematodes like banana & irish potatoes. Widely used in western Kenya, this tree has a great potential for soil improvement on small farms due to nitrogen fixation and leaf mulch.
Croton megalocarpus  (Mukinduri)	Found in Tanzania, Rwanda, Burundi, Uganda, Kenya, Congo (DRC), Malawi, Zambia and Mozambique. In Kenya is wide spread, from the south to the western and northern parts of the country. Found in Ecozones III-IV but very common in zone III, 1000 - 2000 m above sea level and is well adapted to variable highland soils	It may occur in mixed farming systems, woodlots, boundaries and, agroforestry systems	It may be propagated by direct sowing at site (recommended), seedlings (sow seed directly in pots) or wilding. It's fast growing in high potential areas, slow elsewhere; lopping, pollarding and coppicing may be employed.It takes 10 to 25 years to mature.	Firewood (smoke may irritate eyes), timber, charcoal, poles, medicine (bark), bee forage, shade, ornamental, mulch, live fence, boundary planting (popular among Kikuyu) and, veterinary medicine	Seed has high oil (30%) and protein content(50%). Oil extract can be a strong purgative. It is not recommended for intercropping due to competition and shade. Cultural beliefs prevent it from being planted close to homes
Cordia abyssinica / Cordia africana  (Muringa)	A large deciduous forest tree of moist warm areas, woodland and bush. Widespread in Kenya, common in pasture land between 1,200 and 2,000 m. mainly in Central Province, around Nairobi, in Meru, Marsabit, Kakamega, and Kisii Districts and in parts of Rift Valley Province. Tends to be riverine in drier areas. Ecozones II - III.	Plantation, mixed woodlots, amenity, agroforestry	Propagation; wildings and seedlings. Moderate to slow growing; taking 30 - 60 yrs to mature. Pollarding, lopping and coppicing may be applied. Several seedlings may germinate from each stone. Can be pricked out. Young trees grow best under some shade. Tend to branch a lot if grown in full light.	Timber, firewood, furniture, beehives, utensils (mortars), edible fruit, medicine (bark, roots), fodder (dry season), bee forage, shade, ornamental, mulch, soil conservation, fibre, glue, boundary marking.	The heartwood is hard and takes a good polish, so the timber is prized for furniture, but it can be twisted and difficult to saw. Often found in cropland where it is managed to reduce shade. Provides very good mulch.
Markhamia lutea  (Zusiala)	A tropical African tree common in the lake basin and highland areas, to 2,000 m. It stands acid heavy clay soil, but not waterlogging; prefers red loam and has deep roots. Ecozones II-III	Plantation/ amenity/ agroforestry systems	Propagated by use of seedlings and wildings. Are fast growing and coppicing may be employed in their management. They take between 15 - 30 yrs to mature	Firewood (domestic as well as tobacco curing), charcoal, timber, furniture, poles, posts, tool handles, walking sticks, boat building, banana props, medicine (leaves), bee forage, shade, ornamental, mulch, soil conservation, windbreak, ceremonial, boundary marking.	The species is widely used in western Kenya. The wood is fairly termite resistant.
Markhamia lutea  (Siala)	1400 III Red loam to clay loamy soil	Plantation/ woodlot/ amenity  agroforestry systems		Timber/ amenity/  soil nutrient input	Short (15 - 30 yrs)
Calliandra calothyrsus	0 - 1400 III Variable	Agroforestry system		Fuel, soil  nutrient enhancing	Short
Casuarina equisetifolia (Whispering pine)	Occurs naturally on tropical sea shores - Pacific and Indian Oceans, making it theCasurina with the widest natural distribution.In Kenya is common along the coral beaches and nearby hinterland, 0-1,400 m. The extensive root system enables it to grow in poor soils. It tolerates salty winds and poor, salty and sandy soils of the beaches. Ecozones I-IV but limited to the coast. Seeds at the coast mainly in July - August and February - March	Plantation/ agroforestry	Seedlings and wildings may be used. Produces root suckers if roots are exposed. Nursery soil where they are to be raised may need inoculation by addition of soil from beneath mature trees. Are fast growing and prune to get clear bole. Coppices when young, but less vigorously than C.cunninghamiana.. Takes 4 - 6 yrs to mature)	Firewood (burns very well), charcoal, furniture, poles (for house construction), posts, boat building (dhow masts), tool handles, fodder, shade, ornamental,mulch, nitrogen-fixing, soil conservation, reclamation of degraded areas, sand-dune stabilization, windbreak, tannin, dye	The species is said to exhaust soil moisture and lower the water table, and is tolerant to salt water. It suppresses undergrowth and dry needles on the ground may become a fire hazard. The species is reputed to be one of the best fuel species in the world.
Gliricidia sepium  (Mother of cocoa)	A tree or shrub, wide spread in the tropics due to its many uses and speed of growth. Grows in a variety of soils, both acidic and those low in fertility, mainly in humid lowlands, 0-1,600 m. In Kenya it also does well in drier areas like Kitui and Isiolo. Ecozones III-VI.	Woodlots/  agroforestry systems	Propagation is by seedlings, cuttings, direct sowing at site(cuttings are best option for live fence). Are fast growing; coppicing, pollarding & lopping may be employed	Firewood, poles, fodder (leaves, pods, seeds for ruminants and shoots), bee forage, shade,mulch,ornamental, nitrogen fixing, soil conservation, windbreak, live fence, stakes.	The Latin name means "rat-killer" as a poison can be made from the leaves which is toxic to rats as well as other non-ruminants like pigs, donkeys and horses. Bark, roots and seeds may also contain poison. A very useful quick fence can be grown from crossed stakes which soon sprout. Wood is resistant to termites
Leucaena leucocephala  (Lusina)	Widely introduced in the tropics, grows well at altitudes of 0-1,600 m, in full sunlight and in well drained neutral or calcareous soil.Does not tolerate acidic soils. Needs more than 600 mm rainfall. It is naturalized and to some extent invasive in some parts of Kenya with moist ground and warm climate. A psyllid insect pest, Heteropsylla cubana, causes defoliation. In Kenya, the psyllid defoliates the leucaena, resulting in severely reduced production of fodder as well as wood, but without killing the leucaena. Ecozone II-V	Woodlots/ mixed agroforestry systems	Propagation is via Seedlings and direct sowing at site. Is very fast growing on suitable sites; pollarding, lopping and coppicing may be employed. It can become a weed.	Firewood, poles, medicine (roots), fodder (leaves and shoots), bee forage, shade, mulch, nitrogen fixing, soil conservation and improvement, windbreak, tannin, dye	The species exhibits great variation. The mimosine in the leaves can cause hair loss, infertility and stomach problems in livestock, especially non-ruminants like donkeys. Livestock feed should not contain more than 20% Leucaena
Acacia tortilis	Common in most of dry Africa from North and West Africa to South Africa. Wide spread in lowland arid and semiarid areas of kenya. Tolerates a wide range of soils, from sandy, silty to black-cotton soils. May be dominant on dry red soils and prefers slightly alkaline conditions. Often stands along rivers, 0-1,650 m. Can grow in shallow soils is among the most drought-resistant of the acacias in Kenya. Rainfall 150-900 mm. Ecozones IV-VII	Mixed enrichment/ agroforestry	Propagation is by seedlings, wildings, direct sowing at site (seeds taken straight from pod rarely germinate due to seed dormancy), It's slow growing but may grow relatively fast on dry sandy soils if weeding is done and goats are kept away. Also withstands moderate lopping and does not coppice well. Prune when young.	Firewood, timber, charcoal, poles, edible pods medicine, fodder (pods and leaves, especially for goats and camels), bee forage, shade (meeting place for Turkana), ornamental, dune fixation, nitrogen fixation, soil conservation, fibre (strings made from bark), live fence, tannin, dye, thorn used as pins or needles, veterinary medicine.	The tree is limited to desert areas. Its pods are popular feed for livestock - are even collected and saved for dry season and even sold in northern Kenya. Should not be planted near homes due to its thorns and the likelihood of attracting caterpillars that feed on it.
Prosopis chilensis  (Algaroba)	Cultivated all over the tropics, it's drought resistant and grows on light sandy soils.Tolerant to extreme temperatures, severe drought, overgrazing and waterlogging but is sensitive to weed competition while young. Introduced in Kenya, e.g. in Baringo, Wajir, Magadi, Mandera and Turkana, 0 - 1,500 m. Prosopis .spp, generally referred to as mesquites, have demonstrated their invasiveness in Kenya especially in irrigation schemes in hot areas. Ecozones IV-VII. Does well in sandy to sandy-clay soils to riverine clay/ sandy soils	Enrichment/  agroforestry systems	It's propagated by seedlings or direct sowing at site. Fairly fast growing even in dry conditions; coppicing, pruning. Leaves and pods can be lopped for goats.	Fodder (pods), firewood, charcoal,soil protection, poles, posts, edible fruit and leaves, bee forage, shade, gum, tannin and live fence	Since the tree has become a weed in wetter areas, planting in cultivated areas should be avoided. There are about 44 mesquites, most of which are found in the warmer parts of the Americas and a few in Asia and Africa.A number of them are terrible weeds.
Melia volkensii  (Mkau)	A valuable tree in the ASALs of Ethiopia and Somalia south to Tanzania. In Kenya is found in Kitui, Mwingi, Machakos, Embu, Taita, Samburu, Isiolo, Makueni, Voi, Tsavo National Park and Moyale in dry bushland or woodland and drier wooded grasslands. Altitude ranges from 400 to 1,650 m and in Ecozones V-VI. Does well in sandy to sandy-clay soils to riverine clay/ sandy soils	Mixed/ agroforestry systems	It may be propagated by seedlings, root cuttings or root suckers, wildings. The tree grows faster if propagated using root suckers. Young trees needs to be protected from goats and coppicing can also be done	Firewood, timber (construction, door frames), medicine (bark), fodder (fruit), bee forage, shade,mulch, soil conservation.	Wood hard, brown, and makes good timber, resistant to attack by borers.It is a highly prized tree in the dry areas where it is intercropped with food crops with no adverse effects and occasionally improved yields.
Tamarindus indica  (Mkwaju)	It is indigenous to tropical Africa; widely used in the Sahel, India, South East Asia, the Caribbean and Central America. A very adaptable species, drought hardy, preferring semi arid areas and wooded grasslands, tolerating salty, coastal winds, even monsoon climates, Altitude ranges from 0 to 1,500 m. Grows in most soils, but prefers well-drained deep alluvial soil; often riverine in very dry areas. Found in Ecozones III-V	Mixed/ agroforestry  systems amenity	Good mother trees are chosen for vegetative propagation. Seedlings, wildings, direct sowing at site, grafting and budding for best varieties. They are slow growing but long lived; pollarding, coppicing and, pruning may be used.	Firewood, charcoal, timber, furniture, poles, posts, utensils (pestles and mortars, carts), boat building, food (edible fruit pulp, pulp also used for souring porridge, drink, fried seeds, seasoning, flavouring), medicine (leaves, twigs, bark, roots), fodder, bee forage, shade, ornamental, mulch, nitrogen fixing, tannin, dye, veterinary medicine	The fruit has many uses and is important for nutrition in many parts of the world, not least in India.

 

 

Non Recommended Species

 

Prosopis chilensis  (Algaroba)

Cultivated all over the tropics, it's drought resistant and grows on light sandy soils.Tolerant to extreme temperatures, severe drought, overgrazing and waterlogging but is sensitive to weed competition while young. Introduced in Kenya, e.g. in Baringo, Wajir, Magadi, Mandera and Turkana, 0 - 1,500 m. Prosopis .spp, generally referred to as mesquites, have demonstrated their invasiveness in Kenya especially in irrigation schemes in hot areas. Ecozones IV-VII. Does well in sandy to sandy-clay soils to riverine clay/ sandy soils

Enrichment/  agroforestry systems

It's propagated by seedlings or direct sowing at site. Fairly fast growing even in dry conditions; coppicing, pruning. Leaves and pods can be lopped for goats.

Fodder (pods), firewood, charcoal,soil protection, poles, posts, edible fruit and leaves, bee forage, shade, gum, tannin and live fence

Since the tree has become a weed in wetter areas, planting in cultivated areas should be avoided. There are about 44 mesquites, most of which are found in the warmer parts of the Americas and a few in Asia and Africa.A number of them are terrible weeds.

 

 

Trees suitable for Eco-Zone II (over 1400 mm rainfall) 

Trees suitable for Eco-Zone III - Highland region (800 -1400 mm rainfall) 

Trees suitable for Eco-Zone III - Lowlands (800 - 1400 mm rainfall) 

Trees suitable for Eco-Zone IV (400-800 mm rainfall) 

Trees suitable for Eco-Zone V-VI (under 400 mm rainfall) 

Information Source Links 

• KEFRI (1990). A guide to tree planting in Kenya / Kenya Forestry Research Institute (KEFRI) - Nairobi, Kenya - E-mail: director@kefri.org - Tel. +254-0724-259781/2, +254-722-157414
• Maundu, P. and Tengnäs, B. (Eds)(2005). Useful trees and shrubs for Kenya. World Agroforestry Centre, Technical Handbook No.35. ISBN 9966-896-70-8.
• KEFRI Seed catalogue. Download KEFRI seed catalogue click here

Introduction

Agroforestry is an old practice, consisting of growing perennial trees and shrubs in association with agricultural crops, pastures and/or keeping livestock in the same field. Agroforestry aims to use agro-biodiversity in generating multiple services. Trees and shrubs provide mulching material, green manure, animal fodder, soil erosion control, shade, nutrient cycling and improved soil fertility and also socioeconomic benefits e.g. saleable products such as fruits, fuel wood and charcoal, timber for construction, craft materials, etc.

The classification of the different types of agroforestry is based on the type of environment and on the combination of the components. In the humid lowland tropics, the broadest range of homegardens and multi-level cropping are found, whereas agro-silvopastoral systems dominate in semi-arid and subhumid zones. In tropical highlands vegetation strips are common, in order to reduce erosion risk. 

Basically, there are three categories of agroforestry systems:

• Agrosilvicultural systems: Trees with crops e.g. taungya and alley cropping
• Silvopastoral systems: Trees with livestock/pasture e.g. trees and shrubs on pastures and multipurpose trees, fodder trees and shrubs grown on or around cropland
• Agrosilvopastoral systems: Trees with both crops and livestock e.g. compound farming.

Next to climatic conditions and soil type, success of agroforestry depends on the right choice of species combination, management practices and the understanding and motivation for using it. An agroforestry system involves two or more plant species and/or animals (including at least one woody perennial), it has more than two outputs and has a cycle of more than one year. 

Distribution of the plant components can vary in space and time. Plant components can be mixed in different densities (see images below) and have a separate long/short cropping/fallow cycle. 

Trees along borders of fields.

© B.T. Kang, IITA (1996)

Alternative rows of plant components.

© B.T. Kang, IITA (1996)

Alternative strips or alley cropping.

© B.T. Kang, IITA (1996)

Random mixture of plant components.

© B.T. Kang, IITA (1996)

Ecological Aspects of Agroforestry

Agroforestry systems have the following basic principles:

• Competition between the plants must be minimised
  This can be achieved by planting the plants in such a way that they are not using resources all at the same time. For instance, acacia trees (Faidherbia albida) loose their leaves during the millet growing season, and are suitable to feed cattle, as their pods are rich of proteins. Therefore, many African farmers grow acacia trees combining with millet and cattle.
• Complementarity among the plants must be maximised
  Complementarity and competition depend on the root system of the crops and trees/shrubs, i.e. on the depth or shallowness of the roots. If one has deep, the other one shallow roots, they will not compete for nutrients and water, but might complement/ benefit from each other.

(Sanchez 1995)

Agroforestry has following advantages:

• Improvement of soil fertility. Trees provide mulch when their leaves, fruits and branches fall down and decompose. This results in an increase of organic matter and recycling of nutrients from deep in the soil, and leguminous trees fix nitrogen that can benefit food crops.
• Effects on soil moisture and microclimate. Shading and windbreak effects of trees influence microclimate and help to conserve soil moisture. Shade helps reducing the soil temperature and the amount of water that evaporates into the air. Though their roots may also deprive crops of moisture.
• Soil conservation. Trees can conserve the soil in many ways. They cushion the impact of raindrops on the soil and reduce the amount of rain-splash erosion. Their roots bind/stabilise the soil. Planted along contours, they can interrupt the flow of water running off the surface. They can act as windbreaks protecting the soil against wind erosion
• Improvement of biodiversity. Agroforestry systems improve diversity and quantity of animals/wildlife by offering a greater variety of habitats

Drawbacks to agroforestry: 

One is labour is required. However, it can be reduced by proper planning. Rows of trees can be planted, weeded and guarded at the same time as the food crops. Surface mulching with leaves involves less labour than digging them in. Any digging needed can be done at the same time as the land is prepared for the crops.

Trees need to be watered and protected when young. Later on they can survive on rain water alone. 
Trees can also lower yields of maize and other food crops. However, if both crop and tree products are taken into account, a higher total yield from unit of land will be achieved than in a monoculture. Though a field of maize may produce a high yield, it is not sustainable in a long run as problems associated with pests and diseases and soil exhaustion will soon lead to decline in yields and higher production costs. 

Interactions in agrosylvicultural systems.

© B.T. Kang, IITA (1996) after Young (1998)

Silvopastoral system.

© B.T. Kang, IITA (1996)

Selection of Trees and Shrubs Species

The multipurpose trees

Following species were found to perform well, in terms of survival, growth, and wood and foliage production, across diverse agro-ecological zones:

• Moringa oleifera
• Senna siamea
• Senna spectabilis
• Acacia auriculiformis
• Leucaena leucocephala (except in acidic soils)
• Some provenances of Gliricidia sepium

Fodder trees

Fodder refers to the green parts of the tree, for example leaves or sometimes flowers and pods, eaten by browsing or grazing animals. Fodder trees include species of Acacia, Leucaena, Prosopis and many others. 
One of the best fodder trees is Calliandra, having high protein content. Calliandra grows up to 4 to 6 metres, requires rainfall above 1000 mm per year and grows well in well-drained soils. Nine months after planting, fodder can be harvested. Harvesting can be done 4 to 6 times per year. 

Criteria for selection of fodder species:

• Edible to livestock and rich in protein
• Easy to manage
• Drought tolerant
• Tolerant of trampling if to be grazed
• Able to resprout easily

Taungya system (shamba system)

The Taungya system combines forestry crops and agricultural crops during the first years of establishment of the forestry plantation. The main objective of taungya is wood production. 
Generally, the land belongs to the forestry departments, who allow subsistence farmers to grow their crops for two or three years. Farmers have to take care of the forestry seedlings, getting in return part or all of the agricultural produce. 

The Taungya system comes originally from Myanmar (Burma) and means hill (Taung) cultivation (ya). In East Africa it is known as Shamba system.

Dispersed trees on cropland

The practice of growing trees in fields while crops are grown alongside or underneath can be done either by protecting and managing the trees that are already there or by planting new trees.

There are different spacing patterns and densities of placement depending on the type of tree chosen and of crop grown, but trees are generally planted at least 8-10 m apart.

Advantages:

• Growing trees with crops can increase crop yields due to shading and the addition of nutrients and organic matter to the soil.
• Trees can be a breeding place for beneficial insects and other creatures that can reduce crop pest numbers.
• Trees can provide products of commercial and subsistence value.

Disadvantages:

• Trees can attract birds and crop pests, which can damage crops.
• Competition with crops for water, nutrients. It is important to plant trees with deeper roots than those of the crops grown alongside.

Compound farming (Home gardens)

Compound farming is also known as home garden, village-forage garden, kitchen garden and household garden. In Africa, they are known as:

• Compound farms in Southeast Nigeria, humid lowlands
• Chagga home gardens in Mt. Kilimanjaro, Northern Tanzania, highlands
• Ka/Fuyo gardens in Hounde region in Burkina Faso, semi-arid to sub-humid lowlands

Compound farming consists on growing trees, shrubs, vines and herbaceous plants in or around the homesteads, aiming mostly food production for household consumption. In home gardens perennial crops and annual crops are grown side by side. Home gardens are characterised by the intensive use of multi-purpose trees, shrubs, food crops and animals. Typical is also the high species diversity and the complex, layered structure (3-4 vertical canopy layers). Near the ground there is a herbaceous layer consisting of plants such as beans, pulses, root crops grasses and medicinal plants, which grow to about 1.5 metres. The middle layer (1-3 m height) consists of small trees that tolerate some amount of shade such as coffee, tea, banana, papaya or food plants such as cassava, etc. The upper layers are usually about 20 metres high and consist of trees for fruit, fuel, timber, shade and fodder. 

Animals are also usually included in the system. 
The Chagga home gardens in Tanzania are based on Arabica coffee and banana for commercial purposes.

Advantages:

• Production of food is continuous and diverse.
• Farmers have easy access to food, timber, fuel, fodder, spices and medicines.
• Home gardens protect the soil and conserve water.
• Labour can be used efficiently because home gardens are situated close to houses.
• Produce may be sold locally and act as a financial buffer in times of need.

Disadvantages:

• The high diversity of plants in a home garden can provide a habitat for species that could become pests or introduce diseases.

Alley cropping

Alley cropping is also known as alley farming or hedgerow intercropping. It consists in growing food crops between hedgerows of shrubs and trees, specially leguminous species. The arrangement of the components is uniform (not mixed), consisting of strips with different widths. 
During growing of the crops, the hedges get pruned regularly, to avoid shading of the crops and to provide biomass, enhancing the nutrient status and physical properties of the soil. 

Alley cropping is developed to improve or maintain crop yields by improving soil fertility and micro-climate through the cycling of nutrients, mulching and weed control. This can be reached by using specific tree species that produce foliage and fix nitrogen, enriching the soil. By planting deep-rooted trees and shrubs that grow quickly in hedgerows, essential plant nutrients are recycled to the benefit of crops planted in alleys between the hedgerows. Furthermore, a good mixture of trees and shrubs can provide animal fodder, protection against soil erosion, shade and windbreaks, fuel wood and construction material. 

Alley cropping is mostly used in humid or subhumid tropical areas on fragile soils and seems to work best where farmers need to intensify crop production but have soil fertility problems.

The technique of alley cropping requires careful planning and management. It is preferable that the species used have a light open crown that lets sunlight pass through onto the crops that are being grown. It is also possible to prune species with a denser crown. The trees used must also be capable of rapid resprouting after coppicing.
 

Alley cropping management cycle

1. The trees are planted in lines and crop grown between the rows.
2. When the shade from the trees begins to interfere with the crops they are coppiced or pollarded.
3. The coppiced branches are placed between the rows. Leaves will fall to the ground adding organic matter to the soil when they breakdown. Branches and twigs can be gathered for fuel or other purposes.
4. Trees resprout.
5. The cycle is repeated.

Advantages of alley cropping:

• Improvement of soil fertility and structure and micro-climate conditions, thereby benefiting crops.
• A longer cropping period and higher land use intensity.
• Trees used can provide products of commercial and subsistence value.

Disadvantages of alley cropping:

• The technique will take some years to establish, so farmers will have to wait for the benefits.
• Farmers may not have the capital available for the investment in trees.
• Alley cropping requires considerable labour and management - results will be poor if planting and pruning schedules are not carried out properly.
• Competition with crops for water and nutrients. It is important to plant trees with deeper roots than those of the crops grown alongside.

Improved Fallows

Fallows are defined as following:
1) Allowing crop land to lie idle, either tilled or untilled, during the whole or greater portion of a growing season. Tillage is usually practised to control weeds and encourage the storage of moisture in the soil.
2) Land rested from deliberate cropping, not necessarily without cultivation or grazing but without sowing.
3) State of land left without a crop or weed growth for extended period, often to accumulate moisture.

Improved fallow is the replacement or enhancement of natural fallow vegetation by the introduction of selected trees or shrubs. The purpose of improved fallow is to shorten the fallow period and/or increase the yield of subsequent crops. This is done by planting trees or shrubs which can help to restore nutrients to the soil and to suppress weeds as well as providing useful by-products. The trees therefore enrich the fallow both biologically and economically.

In this practice the cropping period usually alternates with the tree-growing period. However, it is possible to keep some trees during the cropping period and many farmers have combined the method of improved fallow with alley cropping.

By planting soil enriching species, the minimum fallow period can be shortened from 15 to 20 years to about 8 to 10 years. However in Kenya, Sesbania is grown in a 3 year rotation and Tephrosia in a 1 year rotation.

Advantages:

• The time required for soil enrichment can be shortened; the tree canopy and fast growing species can suppress weeds.
• Soil erosion is minimised.
• The use of a wide variety of species can reduce pests, weeds and diseases.
• This method is relatively inexpensive to establish and maintain.
• The wood can be used or sold at the end of the fallow period.

Disadvantages:

• The planting of seedlings and tree cutting must be done during the same period of crop planting - labour may be a limiting factor at this time.
• The fallow will need protection from browsing animals.

Contour vegetation strips

Contour vegetation strips are living barriers of trees and shrubs which are planted along the contour lines of a slope, in order to control water and soil erosion. These lines of vegetation can also provide useful products such as food, fuel, building poles, fodder or gum.
There are many factors to consider when building contour strips as bad design can lead to even more severe erosion. The effectiveness of the vegetation strips depends on the type of trees planted, the spacing of the trees and the width of the strip, the steepness of the slope, the amount of rainfall and the soil type.

Advantages:

• Strips can provide additional nutrients and organic matter into the soil. This can be increased by using nitrogen-fixing plants.
• Excess vegetation can provide food for animals. These can be allowed to browse through the strip to feed on crop remains after harvesting.

Disadvantages:

• Contour strips take up land which could be used for crops.

Planting on terraces

Terraces are normally used as soil and water conservation measures on slopes. They provide flat areas of land that can be planted with crops. 
Building terraces involves digging ditches and making ridges. Along the contours of a slope, grasses, trees and shrubs can be planted on the ridges, helping to stabilise the ground, providing leaf mulch, protecting crops from wind and providing other useful products such as food, fuel, building poles or fodder.

Trees can be planted on the ridge of the terrace or at the back of the terrace. If the tree is planted at back of the terrace it will get all of its water requirements. If a tree is planted on the ridge of the terrace, it will be on drier ground but the leaves will spread around more evenly and provide more nutrients for crops. Trees can be planted in both locations if the terrace is wide enough.
The type of tree or hedge used will depend on the site it is planted on and on the kind of products or services you wish it to provide. If the aim of the terrace is to stabilise the soil, trees and shrubs with strong roots systems should be planted. These will be able to withstand the movements of soil and water.

Advantages:

• Stabilisation of the slope, which results in soil and water conservation and a better environment for crops to grow in.
• Shelter from wind.
• Pest control by providing a breeding place for beneficial insects.
• Increased area of land that can be cropped.
• Useful by-products such as food, fuel, building poles or fodder.

Disadvantages:

• As the structure of the land is changed quite dramatically, land tenure rights may first need to be established or secured.
• Building terraces require adequate skills and material, labour and capital and also the capacity to maintain the structures for years to come.

Information Source Links

• Franzel, S. and Scherr, S.J. (eds) (2002). Trees on the farm. Assessing the Adoption Potential of Agroforestry Practices in Africa. ICRAF/CABI Publishing. ISBN 0 85199 561 6.
• Garrity, D., Okono, A., Grayson, M. and Parrott, S. (eds.) (2006). World Agroforestry into the Future. Nairobi: World Agroforestry Centre.
• HDRA (2001). Agroforestry in the tropics. HDRA - the organic organisation, UK. www.gardenorganic.org.uk
• Huxley, P. and van Houten, H. (1997). Glossary for agroforestry. ICRAF Nairobi, Kenya. ISBN 929059 124 2
• International Institute of Rural Reconstruction (IIRR). Sustainable Agriculture Extension Manual. Available at www.betuco.be/
• Kang, B.T. (1996). Sustainable agroforestry systems for the tropics: concepts and examples. IITA Research Guide 26. www.iita.org
• Robert, B., Caine, C, Cooper, D., Cousins, B., and Roberts, S. (1998). People's Farming Workbook. Environmental and Development Agency. David Philip Publishers, South Africa. ISBN: 0 86486 431 0
• Rocheleau, D., Weber, F. and Field-Juma, A. (1988). Agroforestry in dryland Africa. ICRAF, Nairobi, Kenya. ISBN 92 9059 049 1
• Sanchez, P.A. (1995). Science in agroforestry. In: Agroforestry systems, Vol.30, Numbers 1-2, 5-55.
• Schroth, G. and Sinclair, F.L. (Eds) (2003). Trees, Crops and Soil Fertility: Concepts and Research Methods. CAB International.
• Young, A. (1990). Agroforestry for soil conservation. Nairobi: ICRAF. CAB International.