Radiation interception and growth of maize/cowpea intercrop as affected by maize plant density and cowpea cultivar

Abstract

Sole and intercropped maize ( Zea mays L.) and cowpea ( Vigna unguiculata (L.) Walp.) were grown to examine how radiation interception and radiation-use efficiency (RUE) changed under intercropping. The work also examined whether intercropping advantage as measured by land equivalent ratio (LER) was determined by the yield of the dominated cowpea crop. In one experiment, maize plant density was varied and in another, it was held constant and 15 contrasting cowpea cultivars were used. Increased radiation interception by the intercrops prior to maize grain filling increased biomass production, particularly at the low maize density. There was, however, no intercropping advantage in RUE. Radiation-use efficiency of the combined intercrop was between that of maize and cowpea in sole cropping, the actual value being determined by the proportion of radiation intercepted by component crops. There was a rather small yield advantage of intercropping, with LER of around 1.1 at the two higher plant densities of maize. At the low maize density of 2.2 plants m −2, however, LER was less than 1.0 despite an increase in partial LER of cowpea. Cowpea yield and partial LER varied greatly among 15 cowpea cultivars when intercropped. There were positive but weak correlations between yield and vegetative dry matter of cowpea, and between vegetative dry matter and radiation transmitted through the maize canopy to the cowpea. Grain yield and partial LER of maize, on the other hand, were similar when intercropped with different cowpea cultivars, and hence variation in total LER reflected mostly the variation in partial LER of cowpea. It is concluded that maize, except when planted at low densities, will dominate cowpea, and the performance of the dominated crop (cowpea) will have most influence on total LER.