Effect of crop rotation and nitrogen fertilization on yield and nitrogen efficiency in maize in the northern Guinea savanna of Nigeria

Two crop rotation cycles were evaluated to determine the effect of cropping systems and N fertilization on the yield and efficiency of N in maize. Maize was grown on plots which had previously supported monocrops of two genotypes each of soybean (TGx 1448-2E and SAMSOY-2) and cowpea (IT 96D-724 and SAMPEA-7), natural fallow and maize. In a split-plot experimental design, three N fertilizer rates (30, 60 and 90 kg ha(-1)) and an unfertilized control were compared. On average, maize following legumes had higher grain yield of 1.2 and 1.3-fold compared with maize after fallow or maize after maize respectively. Similarly, legume rotation resulted in significant increase in total N uptake compared to continuous maize. In both years, N agronomic efficiency (AE(N)) and N fertilizer recovery efficiency (REN) of maize following grain legumes were on average 14 and 34% greater than of maize following maize and 12 and 20% greater than of maize following fallow respectively. On the other hand, all N efficiency indices except N physiological efficiency significantly decreased with increasing N levels. These indicate greater N use efficiency for the legume-rotation and poor efficiency for maize monoculture as well as the inefficiency of the current method of N fertilizer application.