The combined effects of nitrogen fertilizer and density of the legume component on production efficiency in a maize/cowpea intercrop system

The combined effects of applied nitrogen and of legume density on the yields and efficiency of cereal/legume intercropping were examined, using maize and cowpea. The levels of applied nitrogen were 0, 30, 60 and 120 kg N ha⁻¹, and intercrop cowpea densities were 80 000, 100 000, 120 000 and 150 000 plants ha⁻¹. The interaction of applied N and density of companion cowpea on yield of maize was negative. In maize, the yield losses due to intercropping were alleviated to some degree by N application, but in cowpea they were accentuated, and it appeared that maize was more competitive than cowpea. Maize was more efficient than cowpea in the utilization of N to produce grain; with each increment of N, efficiency declined in maize but was almost constant in cowpea. The Land Equivalent Ratio (LER), a measure of the efficiency of intercropping, declined with increasing levels of applied N but did not change significantly when intercrop cowpea density exceeded 100 000 plants ha⁻¹. The LER values followed trends in cowpea rather than maize yields, and this may be attributed to shading of cowpea by maize.