Soil-mediated effects of cover crops on weed-crop competition

According to the Resource Pool Diversity Hypothesis (RPDH), increasing cropping system diversity (e.g., crop rotation, fertility sources, and weed management) should increase soil resource pool diversity, and mitigate weed-crop competition intensity. Despite the growing interest in cover crop mixtures to provide weed control, our study is the first to test the effect of cover crop species and functional diversity on weed-crop competition intensity. We hypothesised that according to the RPDH, increasing cover crop species and functional diversity will mitigate weed-crop competition intensity. Using soils collected from a long-term field experiment comparing diverse cover crop mixtures to their mono-species counterparts, we investigated in a greenhouse whether the legacy of cover crops in the soil would alter the intensity of competition that two competitive weeds can exert on maize. No relationship between the relative weed-maize competition intensity and cover crop diversity was found, which failed to support our hypothesis. Nevertheless, the cover crop treatments varied in their effects on weed-crop competition intensity, with the cover crop mixture consisting of triticale, Austrian winter pea and crimson clover resulting in the lowest weed-crop competition intensity and highest maize biomass, regardless of the weed species competitor. Therefore, while cover crop legacies in the soil may affect weed-crop competition, increasing diversity alone is not sufficient to reduce competition intensity. Future research should investigate potential mechanisms driving cover crop legacy effects on weed-crop competition, especially in a field, where diversity in soil resources is likely to be greater compared to pots in a greenhouse.