8. SOME AGROFORESTRY PRACTICES IN KENYA                   

8.8 Alley cropping

Spatial arrangement

Alley cropping is an agroforestry practice where crops are grown between lines of trees and / or shrubs that are managed and spaced at regular intervals in cropland. This practice has received much research attention and is regarded as having promise for solving problems of declining soil fertility in situations where farmers cannot afford to use inorganic fertilizers at the recommended rates.

Areas where the practice is relevant

The practice of alley cropping is not yet widespread among farmers in Kenya. Research findings indicate that alley cropping is not feasible where average rainfall is less than 800 mm annually. The practice has its major potential in humid lowlands, e.g. in the coastal strip. Since the technology is labour demanding, it is relevant mainly in areas with small farms and a high population density or, in other words, where labour is not a limiting factor.

Figure 8.9 One form of alley cropping

Establishment and spacing

The establishment of hedgerows requires many trees or shrubs and therefore a cheap propagation method is called for. Direct seeding or use of cuttings would be ideal, but so far seedlings have been used in most research experiments. If seedlings are to be raised, on-farm nurseries are recommended since growing the relevant species does not require much skill. Calliandra may be an exception due to the scarcity of seed supplies in Kenya, and expensive seeds are often imported.

The spacing used in field trials has ranged from 4 to 8 m between rows and from 0.25 to 2.00 m within rows. In humid areas, close spacing can be tolerated, but in drier conditions a wider spacing is required if competition for moisture is not to be too severe.

On flat land, hedgerows should be oriented in an east-west direction to reduce shading. On sloping land, hedgerows must be oriented along the contours.

Figure 8.10 Tree spacing in alley cropping

Management aspects

Intensive management is required. The first coppicing is done 6-18 months after establishment, depending mainly on growth rate. The frequency of cutting depends on what type of wood is preferred, and on whether or not some reduction in crop yield due to shade can be tolerated. If the leaves are to be used for green manuring or fodder, frequent (up to monthly) prunings are required, but if firewood or staking material is the desired output, cutting should perhaps be only yearly. With yearly cuttings one would, however, expect some loss in crop yield due to shade unless the shrubs are regularly pruned.

Benefits

The focal point in research has been the potential for sustaining or improving soil fertility. Other important benefits can be fodder, small-size wood and improved microclimate. Labour has sometimes been regarded as a constraint since the management of hedgerows requires a lot of work. Competition for moisture has been recognized as an obstacle for this technology, becoming increasingly severe the drier the conditions. The technology is not recommended at all where the annual average rainfall is less than 600 mm. Leucaena often turns into a weed in warm and moist areas, and lately the Leucaena psyllid (see Section 5.6) has appeared as a threat to Leucaena in Kenya.

Examples of species

Leucaena leucocephala, Calliandra calothyrsus, Gliricidia sepium and Cassia siamea have been tried with relative success in Kenya. Sesbania spp. have also been tried but are short lived and normally have a high mortality rate after cutting.