Weed community characteristics and crop performance: a neighbourhood approach

Summary The presence of weeds in crop fields often causes yield reductions. However, the effects of weed diversity have not been fully examined. This study tested the hypothesis that, holding density constant, increased weed species richness would decrease the effects of competition on spring wheat target plant performance. Measurements were taken from circular neighbourhoods (16.5 cm radius) with a single spring wheat plant surrounded by combinations of Setaria viridis , Avena fatua , Kochia scoparia , Thlaspi arvense and spring wheat plants, representing all combinations of neighbour species at four density levels. Using regression models, we found that species richness had no significant direct effect on spring wheat biomass, yield, or relative growth rate and that there were no significant neighbour species interaction terms. For weedy target plants, the presence of negative interaction terms suggested that increasing species richness had negative effects on growth of individual weed species. Additional analysis suggested that increased species richness may limit competitive ability of dominant weeds. Although we found no evidence of a direct effect of weed species richness on crop performance, increased weed species richness had no negative effect on spring wheat performance. Further, species richness of the weed community appears to influence weedy plant performance, which may offer a future opportunity to influence crop performance.