Effect of phosphorus application in legume cover crop rotation on subsequent maize in the savanna zone of West Africa

The benefit of planted fallow with legume cover crops may be limited on P d eficient soil. A trial was conducted at two P deficient sites in northern N igeria to test the hypothesis that application of P to legume cover crop fa llow can substitute for N application to subsequent maize. Mainplots consis ted of leguminous fallows followed by unfertilized maize, or native (mostly grass) fallows followed by maize with 0 or 40 kg N ha(-1) (Kaduna) and 0, 30 or 60 kg N ha(-1) (Bauchi). Three rates of P (0, 9, and 18 kg ha(-1)) we re applied to fallow sub-plots as single superphosphate. In the first year, dry matter accumulation of lablab (Lablab purpureus) responded to P applic ation, while mucuna (Mucuna cochinchinensis) dry matter did not. Lablab mul ch dry matter during the dry season was significantly increased by previous season P application while mucuna was not. Previous fallow vegetation was a significant factor for maize growth in the second year but the interactio n with P applied to the fallow was not significant at P < 0.05. Substantial and similar yield increases were achieved with application of N fertilizer to maize and from application of 9 kg P ha(-1) to previous lablab. Dependi ng on local economic circumstances, a good use of expensive inorganic ferti lizer might be to apply P sources to cover crop legumes to profit from addi tional N benefits as well as residual effects of applied P.