INVESTIGATING COMPONENT SPECIES PROPORTIONS IN A CEREAL-LEGUME COVER CROP MIXTURE UNDER ORGANIC MANAGEMENT

Cover crop mixtures of cereals and legumes are of particular interest to growers because the combination of these two functional groups provides the opportunity to maximize biomass production while also fixing atmospheric nitrogen. Performance of the cover crop, however, will depend in part on the relative proportions of the component species in the mixture, and a better understanding of the effect of species proportions on performance could ultimately lead to more-informed seeding rate recommendations. In a 2008-2009 study, a proportional replacement series design was used to investigate how component species proportions (seeding rates) of a cereal rye (Secale cereal L.) and hairy vetch (Vicia villosa Roth) winter annual cover crop mixture affect rye and vetch field densities and biomass production. Treatments consisted of a gradient of 7 rye:vetch mixture proportions from 100% rye (94 kg/ha) to 100% vetch (42 kg/ha). No significant total yield advantages were observed for any of the mixtures, and rye biomass yields relative to monoculture generally dominated vetch relative yields in mixture. Additional research on the nutrient content of mixture residues and their effect on soil fertility patterns following incorporation will be necessary in order to evaluate how sown species proportions affect total cover crop residue quality and how this influences cover crop mixture performance in cropping systems.