Submitted to: Agronomy Journal
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: May 29, 2013
Publication Date: June 21, 2013
Repository URL: http://handle.nal.usda.gov/10113/58342
Citation: Sanderson, M.A., Brink, G.E., Stout, R.C., Ruth, L. 2013. Grass-legume proportions in forage seed mixtures and effects on herbage yield and weed abundance. Agronomy Journal. 105 (5):1289-1297. Interpretive Summary: Knowledge of how the proportions of grasses and legumes in a forage seed mixture affect production and resistance to weed invasion will be useful in guiding the formulation of forage seed mixtures for farmers. Our objective was to test the hypothesis that mixtures with more equal proportions of grasses and legumes in the seed mixture would have greater productivity and fewer weeds than monocultures or mixtures dominated by one or two species. Thirty different mixtures of grasses and legumes (two experiments of 15 mixtures each) were compared for yield along with legume and weed proportions at four sites in Pennsylvania and Wisconsin for three years. The results did not support our hypothesis that seed mixtures with more equal proportions of forage species would perform better than mixtures dominated by one or two species. Overall, grass-legume mixtures had less weed invasion than grass or legume monocultures. Mixtures also produced as much as or more biomass than nitrogen-fertilized grass monocultures. Optimal legume proportions of 30 to 40% or greater were achieved with a wide range of seed mixtures containing different grass and legume proportions. This indicates that farmers have wide flexibility in formulating seed mixtures for specific locations and to achieve specific functions in their forage operations.
Technical 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 invasion. 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 (Festuca pratensis L.), reed canarygrass (Phalaris arundinacea L.), red clover (Trifolium pratense L.), and kura clover (Trifolium 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 yielded more biomass than the average of legume or nitrogen-fertilized grass monocultures. Mixtures with more equal proportions of species in the seed mixture, however, did not yield more biomass or have fewer weeds than other mixtures. Rather, differences in yield were related to the dominant species in the mixture. Optimal legume proportions (30 to 40%) in the harvested biomass were achieved with a wide range of grass and legume seed proportions, which suggests that farmers have wide flexibility in formulating seed mixtures for pastures.