Grass–Legume Proportions in Forage Seed Mixtures and Effects on Herbage Yield and Weed Abundance

Abstract

Formulating grass–legume mixtures requires knowledge of how the proportion of species in a seed mixture (i.e., species evenness) affects productivity and weed abundance. We hypothesized that mixtures with more equal proportions of species in the seed mixture (i.e., greater species evenness) would have greater productivity and fewer weeds than mixtures dominated by one or two species or monocultures. Two experiments with 15 mixtures and monocultures of orchardgrass ( Dactylis glomerata L.), quackgrass ( Elytrigia repens L.), alfalfa ( Medicago sativa L.), and white clover ( Trifolium repens L.) (Exp. 1) or 15 mixtures and monocultures of meadow fescue [ Schedonorus pratensis (Huds.) P. Beauv.], reed canarygrass ( Phalaris arundinacea L.), red clover ( T. pratense L.), and kura clover ( T. ambiguum L.) (Exp. 2) were sown in autumn 2008 at four locations in Pennsylvania and Wisconsin. In each experiment, there were four monocultures, four mixtures dominated by one species, six mixtures dominated by pairs of species, and one equal mixture. Mixtures and monocultures were harvested four to five times each year from 2009 to 2011. Mixtures often had more biomass than the average of legume or N‐fertilized grass monocultures. Mixtures with more equal proportions of species in the seed mixture, however, did not have more biomass or fewer weeds than other mixtures. Rather, differences in yield were related to the dominant species in the mixture. Optimal legume percentages (30–40%) in the harvested biomass were achieved with a wide range of grass and legume seed proportions, which suggested that farmers have wide flexibility in formulating seed mixtures for pastures.