Effects of preceding maize (Zea mays) and cowpea (Vigna unguiculata) in sole cropping and intercropping on growth, yield and nitrogen requirement of okra (Abelmoschus esculentus)

Field experiments were conducted on Alfisols in Nigeria between 1991 and 1993 to determine the residual effect of maize (Zea mays) and cowpea (Vigna unguiculata) on the growth, pod yield and N response of a succeeding okra (Abelmoschus esculentus) crop. Cowpea and maize were grown alone with 30 and 60 kg/ha of N, P and K, respectively, or intercropped with 60 kg/ha as a basal dressing. The preceding crops had a significant effect on soil nutrient changes, okra growth and yield, and N response of ol;ra. Cowpea increased the N, P and K status of the soil in both sole and mixed stands, compared with sole maize. Leaf area, pod weight and marketable pod yield of okra after sole cowpea or the maize/cowpea intercrop were all significantly higher than after sole maize. Although the application of nitrogen to succeeding okra promoted growth and increased pod yield, this was not accompanied by an increase in the pod yield of okra after sole cowpea or the maize/cowpea treatment beyond 45 kg N/ha. The beneficial effects of the preceding maize/cowpea intercrop on soil fertility, okra pod yield and amounts of N required for okra were partly due to the higher rate of basal nutrients applied as compared to the effects following sole cowpea.