Reconciling crop productivity and biodiversity maintenance is one of the main challenges of agriculture worldwide. Moreover, the importance of weed diversity in mitigating yield losses has been identified as one of the top five research priorities in weed science. We tested the hypotheses that (1) not all weed communities generate yield losses and (2) that more diversified weed communities can mitigate yield losses. The study is based on three years of observations of weed densities, weed biomass and crop biomass at four critical growth stages of winter cereals across 54 zones (36 unweeded and 18 weeded). Out of the six communities identified, only four generated significant yield losses in unweeded zones, ranging from 19% to 56%. The number of ears per plant and the number of grains per ear were systematically affected. Only one weed community was capable of reducing 1,000-kernel weight. Weed biomass decreased by 83% over the gradient of weed community evenness, whereas crop productivity increased by 23%. Diversified weed communities limited the negative effect of competitive and dominant species on crop productivity while potentially promoting ecosystem services provided by subordinate species.

Guillaume Adeux  Eric Vieren Stefano Carlesi   , Paolo Bàrberi, Nicolas Munier-Jolain, Stéphane Cordeau