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Three woody legumes were planted as two-year `improved fallows' to evaluate their residual nitrogen (N) effects on two subsequent maize crops under minimum and conventional tillage management. Maize monoculture and cowpea-maize-maize sequence treatments were included as controls. N₂-fixation was estimated using the ¹⁵N natural abundance method to allow the N contribution from the fallows to be partitioned into N₂-fixation and soil N capture. Acacia angustissima accumulated the largest amount of both below-ground and above-ground biomass during the 2-year growth period. Using Hyparrhenia grass as the reference plant, the proportion of N₂-fixed in litter was 56, 55, 84 and 58% for Acacia, Sesbania sesban, Cajanus cajan, and cowpea, respectively, resulting in inputs of biologically fixed N of 122, 84, 96 and 28 kg N ha⁻¹. Maize growth following the legumes for two subsequent cropping …