Intercropping and crop residue incorporation: Effects on soil nutrient status

A maize-melon mixture relayed into a cassava-soybean intercrop was established at Ibadan, Nigeria, between 1995 and 1997 in order to study the changes in soil-nutrient status, that occurred due to soybean intercropping and residue incorporation. The experiment was conducted on a Kanhaplic Haplustalf soil. Soybean was planted in drills between cassava rows after harvesting maize and melon. Soybean stover was recycled into half of the soybean plots. Cassava yield was reduced by about 16% with soybean intercropping without the residue incorporation and by about 11% with incorporation of the crop residue. Soil pH was significantly reduced from an initial 6.0 to 5.7 with soybean intercropping. Organic matter was drastically reduced from an initial 31.0 g kg(-1) to 5.3 g kg(-1) with sole cassava cropping, and to 10.1 g kg(-1) with soybean intercropping and incorporation of crop residue. Total nitrogen (N) was also significantly reduced to about 0.4 g kg(-1) from an initial content of 1.8 g kg(-1) , while the available phosphorus (P) was increased from 1.8 to an average of 4.0 mg kg(-1) . The exchangeable potassium (K) and effective cation-exchange capacity (ECEC) were not significantly affected.