Evaluation of cassava (Manihot esculenta (Crantz) planting methods and soybean [Glycine max (L.) Merrill] sowing dates on the yield performance of the component species in cassava/soybean intercrop under the humid tropical lowlands of southeastern Nigeria

Field study was conducted during 2001/2002 and 2002/2003 cropping seasons to evaluate the effect of cassava planting methods (horizontal or slanting) and soybean sowing dates (4 and 2 weeks before cassava, simultaneous with cassava, 2 and 4 weeks after cassava) on the yield and yield components and biological productivity of the crop species grown in sole and intercrop. The treatments were arranged in a 2 x 5 factorial laid out in randomized complete block design with three replications. Intercropping significantly (P < 0.05) reduced the yield of cassava and soybean compared with their sole crops. Horizontal method of planting cassava (P < 0.05) depressed yield and yield components of the crop species in the mixture. Soybean yields were generally low due to the shading effect of the cassava component in both cropping seasons. In 2001/2002 and 2002/2003, sowing soybean four weeks before cassava increased grain yield than when sown two weeks before, simultaneously, and two or four weeks after cassava planting. There was no interaction effect between cassava planting method and soybean sowing date in the two cropping seasons. Regardless of the cassava planting method used, soybean sown 4 or 2 weeks before cassava gave the highest monetary returns and net profit than soybean sown at any other time in the mixture or by growing the component crops separately.