The agronomic value of annual plant diversity in crop-weed systems

Enhanced crop or cultivar diversity within annual cropping systems could provide important ecological and agronomic benefits. The agronomic effects of annual plant diversity from mixtures of crop species and barley (Hordeum vulgare L.) cultivar types were compared using richness levels of 1, 2, 5 or 10 randomly selected taxa in a greenhouse experiment. Increasing crop richness increased overall crop dry matter production, production stability (i.e., decreased CV for dry matter production) and weed suppression. These agronomic variables tended to level off after a richness of five to six crop species, suggesting that further increases in crop diversity are redundant. Increasing barley cultivar richness increased crop production in one of two experimental runs, but no effects were observed for weed suppression. Increased light interception related to greater plant canopy height variation in diverse mixtures of species could have contributed to increased productivity in the crop richness experiment. The resu...