Testing alley cropping (contour hedgerows) in semi-arid areas on flat and sloping land: soil and water conservation, competition, yields and economic factors. Cas

Abstract

Alley cropping tested by Mungai et al. on flat land, with prunings incorporated into the soil and one in every four rows of maize replaced by trees in the agroforestry plots, showed already in the late eighties/early nineties that alley cropping was unsuitable for flat semi-arid areas, because of its high risks for the farmers. This was mainly due to poor crop yields caused by (i) low biomass production of the trees under the low rainfall conditions in semi-arid areas, not sufficiently improving soil fertility and other soil conditions, (ii) higher than foreseen competition between trees and crops for water and nutrients, because of more overlap of root zones than expected, also away from the trees and also at lower horizons. The work of Kinama et al. in the nineties proved that on sloping land (in our case ca. 15Πcontour hedge rows and mulch on the surface, for a comparable tree system added to maize or cowpea crops, considerably reduced soil loss and to a lesser extent water runoff. It, however, also reduced crop yields considerably, for the same reasons as in alley cropping on flat land. Nevertheless, strong trade-offs between the erosion control and crop productivity need not be a major deterrent to adoption by farmers, provided the trees have direct and significant benefits to farmers such as producing fodder or tree products that can be well marketed.