Integrated soil management for the savanna zone of W. Africa: legume rotation and fertilizer N

Integrated soil management with leguminous cover crops was studied at two s ites in the northern Guinea savanna zone of northern Nigeria, Kaduna (190 d ay growing season) and Bauchi (150 days). One-year planted fallows of mucun a, lablab, and crotalaria were compared with natural grass fallow and cowpe a controls. All treatments were followed by a maize test crop in the second year with 0, 30, or 60 kg N ha(-1) as urea. Above ground legume residues w ere not incorporated into the soil and most residues were burned early in t he dry season at the Kaduna site. Legume rotation increased soil total N, m aize growth in greenhouse pots, and dry matter and N accumulation of maize. Response of maize grain yield to 30 kg N ha(-1) as urea was highly signifi cant at both sites and much greater than the response to legume rotation. T he mean N fertilizer replacement value from legume rotation was 14 kg N ha( -1) at Kaduna and 6 kg N ha(-1) at Bauchi. With no N applied to the maize t est crop, maize grain yield following legume fallow was 365 kg ha(-1) highe r than natural fallow at Bauchi and 235 kg ha(-1) higher at Kaduna. The ben efit of specific legume fallows to subsequent maize was mostly related to a bove ground N of the previous legume at Bauchi, where residues were protect ed from fire and grazing. At Kaduna, where fallow vegetation was burned, ma ize yield was related to estimated below ground N. The results show that le gume rotation alone results in small maize yield increases in the dry savan na zone.