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Effect of cowpea (Vigna unguiculata) intercropping on weed biomass and maize (Zea mays) yield

Field experiments were conducted to investigate the influence of cowpea (Vigna unguiculata) density (0, 15 or 30 plants/m2) and sowing date (15 days prior to maize sowing or simultaneously with maize), and of maize (Zea mays) planting density (7.5 or 9 plants/m2) on weed biomass and maize crop yield. Results showed that increasing the maize density from 7.5 to 9 plants/m2 reduced the weed biomass by 21.5%. Furthermore, cowpea acted as a living mulch, reducing weed biomass by up to 45.5% and 39.6% when intercropped with maize at a density of 7.5 and 9 plants/m2, respectively. Under weed-free conditions, an increase in maize density from 7.5 to 9 plants/m2 resulted in maize grain yield increasing from 8.92 to 9.40 t/ha; however, the addition of cowpea only increased the maize grain yield by about 4.2%, on average, under these conditions. By contrast, under weed-infested conditions, there was a large decrease in maize grain yield (up to 32%), but intercropping with cowpea reduced this to only a 16% decrease. Under weed-free conditions, there was no effect of sowing date on maize grain yield; however, under weed-infested conditions, yield was greater on the second sowing date. Thus, it is concluded that the planting of maize at a density of 9 plants/m2 and simultaneously intercropping with cowpea at a density of 30 plants/m2 could be an appropriate control measure for weed suppression.