Nutrient availability following planted tree fallows and benefits to subsequent maize crops

Abstract

The effect of a two-year Sesbania and Tephrosia fallow on soil properties and growth of subsequent maize was examined in Zambia. The study was conducted on 18 sites laid in a randomized complete block design with farmers as replicates. The treatments were: Sesbania fallow, Tephrosia fallow, grass fallow, maize with and without fertilizer. Standing biomass plus litter after two years ranged from 5 to 49 mgha-1 for Sesbania and from 3 to 16 mgha-1 for Tephrosia. Both trees increased topsoil inorganic N and anaerobic N mineralisation, as compared to a two-year uncultivated fallow with regrowth of native vegetation and unfertilised maize monoculture. Topsoil inorganic N after Sesbania was directly related to Sesbania biomass (r2=0.80). The yield of unfertilised maize was increased an average of 75% in the season after harvest of Sesbania and 43% in the season after Tephrosia. The residual benefit to maize generally lasted for two cropping seasons after Sesbania and one cropping season after Tephrosia. The magnitude and duration of the residual benefit from Sesbania was directly related to biomass at harvest. We conclude that farmers can use N2-fixing trees to enhance soil properties and improve maize yield in the subsequent season.