Contribution of early season cowpea to late season maize in the savanna zone of West Africa

In the moist savanna zone with a 180 to 190 day growing period, early seaso n cowpea immediately followed by a late season cereal crop can maximize the benefit of the legume to the cereal. Traditional cereal crops for this sys tem are miller and sorghum but new early maize varieties can also be used. A study was conducted to estimate the contribution of the early season cowp ea to late season maize during three years on two fields in central Kaduna State in northern Nigeria. Without insecticide application, early season co wpea grain yield averaged almost 500 kg ha(-1) over all environments includ ing a site where P deficiency was corrected in the second year. N content o f cowpea residues after grain harvest averaged approximately 15 and 30 kg h a(-1) at the low-P and moderate-P sites, respectively. Mean maize grain yie ld without urea or previous cowpea (290 kg ha(-1) in five environments) was increased to 760 kg ha(-1) with urea application (30 and 60 kg ha(-1) trea tments combined) and 690 kg ha(-1) after early season cowpea (three varieti es combined). Maize grain yield after early season cowpea without N applica tion to maize was maintained at levels higher (at p < 0.06) than 30 kg N ha (-1) as fertilizer. Thus, cowpea cultivation in the early season appears to be an effective indigenous solution for supplying a small amount of N for cereal production. The study showed the importance of adequate P availabili ty for the rotation system to succeed.