Strip Crops and Intercrops Outperform Crop Rotations for Weed Management Under Conservation Agriculture in Zimbabwe

Résumé fourni par la source

ABSTRACT High weed infestation remains a major constraint on crop productivity for smallholder farmers practising Conservation Agriculture (CA). Fewer, more diverse weeds are desirable to reduce competition and provide ecosystem services. Crop diversification can help, but it is not yet clear which species combinations and layouts are most effective for smallholder CA. Here, we conducted an experiment in sub‐humid Zimbabwe at two research stations with contrasting soils, and over two growing seasons (2021–2022 and 2022–2023). We evaluated weed community responses to maize monoculture, maize rotated with cowpea or pigeon pea, maize‐pigeon pea intercropping and maize‐cowpea and maize‐pigeon pea strip cropping under moderately fertilised versus unfertilised conditions. Data were collected on weed abundance (number and biomass), diversity (species richness, Pielou evenness and Shannon diversity) and community composition. There were significant differences between sites and, to a lesser extent, between growing seasons. More substantial impacts of cropping systems on weeds were observed at the more fertile site. On average across both sites, seasons and fertiliser levels, maize‐pigeon pea strip cropping performed best, resulting in the lowest weed number (23.2 weeds m −2 ) and biomass (99.2 g m −2 ) and the highest weed species diversity (Shannon index = 1.35), while the maize‐cowpea rotation performed worst (number = 31.3 weeds m −2 , biomass = 179.3 g m −2 and Shannon index = 1.12). Cropping system biomass was associated with lower weed biomass, but had no consistent effect on weed numbers or diversity. Fertilisation had weak and inconsistent effects. Overall, our results suggest that high biomass cropping systems, such as maize‐pigeon pea strip cropping, could contribute to sustainable weed management in Zimbabwe. However, more research is needed to develop strategies for less fertile sites, where weeds seem less susceptible to crop competition.

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