Soil chemical properties and legume-cereal rotation benefits in an Ultisol in Nsukka, Southeastern Nigeria

This research was conducted at the Department of Soil Science, University of Nigeria Teaching and Research Farm in 2008 and 2009 growing seasons. The objective was to evaluate the effects of edible grain legumes (cowpea and soybean) and velvet-bean/maize rotations on soil chemical properties and the contribution of these chemical properties to rotation benefit conferred on the maize by velvet-bean, cowpea and soybean. The experimental design was a factorial fitted into randomized complete block design comprising of four crop rotation systems, two nitrogen levels and two residue management options as factors replicated thrice making a total of 48 plots. Each year entailed two cropping sessions, first, the four crops (cowpea, soybean, velvet-bean and maize) were grown on separate plots and after harvest; maize was grown in all the plots to test for rotation effect. The result showed that the soil chemical properties nitrogen (N) and magnesium (Mg) were significantly higher in the legume-cereal rotations than in continuous maize in both years. Other chemical properties varied in the two years and between legume/maize and continuous maize rotations. Maize yield was significantly increased by velvet-bean/maize rotation in both years. Maize grain yields were also higher in cowpea/maize and soybean/maize rotations than in continuous maize but they were not significantly different. There was also significant rotation residue interaction effect with velvet-bean/maize rotation x residue having the highest maize yield. Regression analysis showed that 37 to 51% changes in maize yield were contributed by N, Mg and potassium (K).