Dry-season sesbania fallows and their influence on nitrogen availability and maize yields in Malawi

Nitrogen deficiency is widespread in southern Africa, but inorganic fertili zers are often unaffordable for smallholder farmers. Short-duration legumin ous fallows are one possible means of soil fertility restoration. We monito red preseason topsoil (0 to 20 cm) ammonium and nitrate, fallow biomass pro duction and grain yields for three years in a relay cropping trial with ses bania [Sesbania sesban (L.) Merr.] and maize (Zea mays L.). Sesbania seedli ngs were interplanted with maize during maize sowing at 0, 7400 or 14,800 t rees ha(-1), in factorial combination with inorganic N fertilizer at 0 or 4 8 kg N ha(-1) (half the recommended rate). After maize harvest, fallows wer e allowed to grow during the seven-month dry season, and were cleared befor e sowing the next maize crop. Both sesbania fallows and inorganic N fertili zer resulted in significantly greater (P < 0.01 to 0.05) preseason topsoil nitrate-N than following unfertilized sole maize. In plots receiving no fer tilizer N, preseason topsoil inorganic N correlated with maize yield over a ll three seasons (r(2) = 0.62, P < 0.001). Sesbania fallows gave significan tly higher maize yields than unfertilized sole maize in two of three years (P < 0.01 to 0.05). Sesbania biomass yields were extremely variable, were n ot significantly related to sesbania planting density, and were inconsisten tly related to soil N fractions and maize yields. Short-duration fallows ma y offer modest yield increases under conditions where longer duration fallo ws are not possible. This gain must be considered against the loss of pigeo npea (Cajanus cajan L. Millsp) harvest in the similarly structured maize-pi geonpea intercrop common in the region.