Legume-maize rotation effect on maize productivity and soil fertility parameters under selected agronomic practices in a sandy loam soil

Inclusion of legumes in cropping systems is essential for sustainable management of farming systems and reducing the nitrogen (N) fertilizer requirement for maize production. The study evaluated the effect of growing legumes (soybean, cowpea and velvet bean) and maize the same year in rotation, on maize yield and soil fertility indices. The agronomic practices implemented were residue management (residue added and residue removed) and fertilizer N application (0 kg N ha^-1 and 60 kg N ha^-1) under four rotation systems. The result showed that growing velvet bean the same year in rotation with maize was effective in increasing maize yield and improving some soil fertility indices over growing maize after maize the same year in the same location. Compared to maize monocropping, over 100% increase in maize yield was obtained with velvet bean-maize rotation even in absence of residue incorporation. In addition, velvet bean-maize rotation increased maize yield over cowpea- and soybean- maize rotations. The rotation effect occurred as a result of improvement in soil nitrogen, avail phosphorus (P), exchangeable magnesium (exch Mg) and effective cation exchange capacity (ECEC). Grain legumes-maize rotations equally increased maize yield over sole maize. Generally legume-maize rotations increased total N, avail P, exch K, Mg and effective cation exchange capacity over sole maize. Crop residue incorporation and N fertilizer application significantly improved soil N and maize grain yield (0.18%, 2.74 tha^-1 in 2008; 0.22%, 1.16 tha^-1 in 2009 and 0.19%, 2.72 tha^-1 in 2008; 1.35 tha^-1 in 2009 respectively) over non-residue incorporation (0.16% and 1.84 tha^-1 in 2008, 0.66 tha^-1 in 2009) and zero N application (0.16% and 1.83 tha^-1 in 2008 and 0.17% and 0.85 tha^-1 in 2009). Therefore, velvet bean could be planted the same season with subsequent maize in rotation cropping for intensive sustainable maize production in sandy-loam soils without fertilizer N. For grain legumes such as soybean and cowpea to be effective in rotation cropping with maize, the grain legumes have to be planted early before the full set of rain because excess rain would affect their growth and development.