Legumes for improving maize yields and income in semi-arid Kenya

An experiment was conducted at the research station of the International Centre for Research in Agroforestry (ICRAF) at Machakos, Kenya from November 1989 to February 1996 to evaluate the effect of annual and perennial legumes on soil fertility, cereal yields and economic returns. The study evaluated six cropping systems: (1) continuous sole maize, (2) maize rotated with short-duration legume, cowpea (Vigna unguiculata L. Walp.), (3) maize rotated with long-duration legume, pigeonpea (Cajanus cajan L. Millsp.), (4) maize intercropped with pigeonpea (5) hedgerow intercropping of maize and a perennial legume, gliricidia (Gliricidia sepium), and (6) continuous sole maize, green-manured with gliricidia prunings produced from an equivalent area outside the cropped field ('biomass transfer technology'). Maize-cowpea sequential and pigeonpea/maize intercropping systems produced, respectively, 17 and 24% higher maize yields than continuous sole maize, but maize-pigeonpea rotation yielded only marginally better. Hedgerow intercropping did not increase maize yields because increased yields during the few high rainfall seasons did not compensate the yield losses in other seasons due to the competition of hedgerows for water with crop. Green manuring with gliricidia prunings increased maize production by 27%, but this technology was not economical because of high labour costs for production and application of prunings to the crop. The annual grain legume-based cropping systems were 32-49% more profitable than continuous sole maize, making them attractive to small farmers in semi-arid tropics. Both cowpea and pigeonpea were affected by pests and diseases, which indicated the need for integrated pest management for realising the potential benefits of these legume-based systems. (C)2000 Elsevier Science B.V. All rights reserved.