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 (AEN) 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.
Key words: Fallow, grain legumes, maize, N uptake, N use efficiency, N fertilizer recovery efficiency.
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