PRODUCTIVITY OF HEDGEROW SHRUBS AND MAIZE UNDER ALLEYCROPPING AND BLOCK PLANTING SYSTEMS IN SEMIARID KENYA

A field experiment was conducted for eight cropping seasons from 1988 to 1991 in semiarid Machakos, Kenya, to compare the productivity of sh rubs and crops in intercropping (alleycropping) versus block (sole) pl anting systems. The study, conducted in a split-plot experiment with t hree replications, consisted of two tree species (Leucaena leucocephal a and Senna siamea syn. Cassia siamea) in the main-plots and combinati ons of two planting systems (alleycropping and block planting of the s hrubs and maize) with five different ratios of land allocation for the shrub and crop (100:0, 15:85, 20:80, 25:75, and 0:100) in sub-plots. Thus, a sole maize and a sole tree were included in the subplot treatm ents. The spacing between hedgerows of shrubs in intercropping was 6.7 , 5, and 4 m, respectively, corresponding to 15, 20, and 25% land allo cation to shrubs. The trees were pruned to 0.5 m height four times a y ear. Intercropped hedgerows of senna and leucaena produced 10% and 24% more biomass than their respective block planting systems. On average , leucaena produced more biomass than senna. Maize alleycropped with l eucaena yielded 16% less grain than sole-crop maize, whereas senna int ercropping caused hardly any maize-yield reduction. Compared with the respective sole-crop systems, leucaena intercropping did not affect la nd equivalent ratio (LER), whereas LER increased by 28% with senna int ercropping. The different tree:crop land occupancy ratios did not affe ct the production of either the component species or of the total syst em, except that LER declined with increased spacing between hedgerows. It is concluded that in semiarid highlands of Kenya, leucaena and cro ps should better be grown in sole blocks, not in alleycropping. In the case of slow-growing species such as senna, intercropping is worthwhi le to consider only if the additional labour needed does not pose a se rious problem for management, and the species has fodder value.