Do intercropping and mineral nitrogen fertilizer affect weed community structures in low-input maize-based cropping systems?

Weeds are a major threat to crop growth in sub-Saharan Africa (SSA), particularly in low-input cropping systems. We investigated the effect of different cropping systems and nitrogen fertilizer on weed infestation during the 2017/18 and 2018/19 cropping seasons in Goromonzi district, Zimbabwe. The objectives of this study were to (1) determine if and how weed composition and structure are affected by intercropping maize with either an improved or landrace cowpea variety compared to sole crops of maize and of improved or landrace cowpea; (2) if and how weed composition and structure are affected by nitrogen fertilization; and (3) how the subsequent changes in weed infestation affect grain yield. Weed parameters were measured at different dates during the cropping cycle, and grain yield was measured at harvest. Significant differences were observed for the density of the 21 weed species collected in two seasons; seven of these weed species had a relative density exceeding 5%. Significantly more weeds were recorded in sole maize compared to sole cowpea. Intercropping significantly reduced the density of C. benghalensis. In sole crops, application of mineral nitrogen fertilizer significantly affected weed density, diversity, richness, and groundcover. Maize grain yield was independent of weed biomass and density, in both sole crops and intercrops. However, increase in weed biomass significantly reduced cowpea yield. Our results suggest that growing sole cowpea reduces weed infestation, therefore, cowpea should be considered as one of the options for effective weed control in subsistence farming communities, where access to herbicides is lacking.