14. agroforestry research in kenya: an overview

14.9 Discussion of research findings

General

Both research and extension efforts over the last 15 years have revealed the extreme complexity of agroforestry systems. Research methods used earlier in agriculture and forestry are not applicable to agroforestry, and new and innovative research approaches are being developed. The importance of the socio-economic dimension of agroforestry has gradually become recognized.

One of the most important results to come out of agroforestry research and development has been the realization of the importance of involving the farmer both in designing research and in extension planning. The research conducted by ICRAF, and by national institutions supported by ICRAF, follows a logical sequence starting with diagnosis of the problems and potentials in the land-use system of an area, followed by the design of appropriate research studies and eventually the design of appropriate interventions to improve land use. The views expressed by farmers are the cornerstones in this process.

Ethno-botanical surveys have more recently become common as part of the D&D process. Understanding the local use of trees and shrubs paves the way for consideration of a wider range of species, including more indigenous species, than used to be common in agroforestry research. Biodiversity considerations have become part and parcel of agroforestry.

Recent research findings have shed new light on many aspects of agroforestry. For a deeper analysis of current knowledge on agroforestry, reference is made to other ICRAF publications. Only a few comments are made in this section.

Agroforestry and soil fertility

So far, much agroforestry research has aimed at evaluating the suitability of technologies like hedgerow intercropping. The potential of agroforestry for addressing problems of soil fertility and sustainability of production systems has been a focal point.

Research results on hedgerow intercropping have, however, been inconsistent. It has been realized that there is a need for more research aimed at quantifying the variables in tree-crop interactions in order to explain why hedgerow intercropping yields the desired results in some environments and not others.

Recent findings on the extent of shrub root systems indicate that the root systems extend much further than was thought earlier. These findings indicate a major weakness in much of the research carried out so far since the research plots have often been so small that roots from adjoining plots interfere with control plots and other neighbouring plots. Thus many of the experiments carried out would have lacked a proper control.

ICRAF scientists have recently proposed a tree-crop interaction (I) equation in order to quantify the effects of the various factors on alley cropped maize yield:

I = F-C + M ± P + L

where F is the benefit of prunings (nutrients and mulch effects); C is the yield reduction due to interspecific competition; M the consequences of microclimatic changes in temperature, light and humidity; P the consequences of changes in soil physical properties; and L is the reduction in losses of nutrients or water (Akyeampong et al, 1992).

It appears that F and C are the most important of these factors. The limited evidence so far suggests that in a dry environment C (yield reduction as a result of competition) is greater than the benefits of mulching (F).

Tentative conclusions from the research on hedgerow intercropping are that:

• Hedgerow intercropping may not be a feasible technology in dry areas (less than 800 mm rainfall a year)

• Hedgerow intercropping with certain species, e.g. Leucaena, is not a feasible technology on acidic soils (most soils in the high-potential areas in Kenya are more or less acidic)

• Hedgerow intercropping may not be feasible where labour is a constraint

• There is a need for further research on hedgerow intercropping before the technology is taken up for extension to farmers.

Fodder production from agroforestry systems

The role of fodder shrubs and trees has been subject to research at several sites in Kenya. Studies carried out by KARI and ILCA in the coastal zone have shown that Leucaena fodder supplemented with Napier grass results in higher milk production if the Napier grass is mature (150 cm high) and hence low in protein. With cross-breed cattle there is a potential for increasing milk production, both during early lactation if the Napier grass is low quality and later during the lactation. Leucaena supplements also result in weight increases except during early lactation when the animal's weight is bound to drop anyway. A general recommendation is to cut Napier grass when it has reached a height of 100 cm rather than 150 cm.

With regard to labour, it was observed that some farmers were reluctant to grow Napier grass due to the amount of labour required. An alternative was then developed using cassava to meet energy needs and Leucaena to meet protein needs. This combination requires less labour.

ICRAF scientists have analysed the potential value of prunings from leguminous shrubs (Hoekstra and Darnhofer, 1992). Their analysis indicates that the potential value is considerably higher if the prunings are used for fodder than if they are used as a source of green manure.

The focus of future research

Based on the experiences and results from the research carried out so far the following areas are likely to be priorities for research over the next few years:

• Continued focus on on-farm research and farmer involvement in research planning and implementation

• Concentration on tree products, e.g. fodder, poles/timber, and fruits and other food from trees and shrubs

• Process-oriented research on soil fertility in relation to a few agroforestry technologies

• The role of trees and shrubs for livestock production

• Development of predictive models for studying the tree-crop interface

• For drier areas: More emphasis on managing and improving the utilization of existing vegetation rather than on introduction of new practices. The focus will be on livestock but not necessarily fodder production for zero-grazing systems

• Research on soil fertility in relation to agroforestry is likely to shift from an emphasis on hedgerow intercropping to block planting of trees for fertility, improved fallows, etc., in order to seek appropriate technologies for dry areas and acidic soils

• Studies on the effects of incorporation of trees with a litter rich in phosphorus as a complement to nitrogen-fixing species

• Studies on the use of lime and green manure.