Direct and residual contributions of symbiotic nitrogen fixation by legumes to the yield and nitrogen uptake of maize (Zea mays L.) in the Nigerian Savannah

Field experiments were conducted to determine the direct and residual contributions of legumes to the yield and nitrogen (N) uptake of maize during the wet seasons of 1994 and 1995 at the University Farm, Abubakar Tafawa Balewa University, Bauchi, Nigeria, located in the Northern Guinea savannah of Nigeria. Nodulating soybean, lablab, green gram and black gram contributed to the yield and N uptake of maize either intercropped with the legumes or grown after legumes as a sole crop. Direct transfer of N from the nodulating soybean, lablab, green gram and black gram to the intercropped maize was 24.9-28.1, 23.8-29.2, 19.7-22.1 and 18.4-18.6 kg N ha(-1), respectively. However, the transfer of residual N from these legumes to the succeeding maize crop was 18.4-20.0, 19.5-29.9, 12.0-13.7 and 9.3-10.3 kg N ha(-1), respectively. Four years of continuous lablab cropping resulted in yields and N uptake of the succeeding maize crop grown without fertilizer N that were comparable to the yields and N uptake of the succeeding maize crop supplied with 40-45 kg N ha(-1) and grown after 4 years of continuous sorghum cropping. It may therefore be concluded that nodulating soybean, lablab, green gram and black gram may be either intercropped or grown in rotation with cereals in order to economize the use of fertilizer N for maize production in the Nigerian savannah.