Rye-Vetch Mixture Proportion Tradeoffs: Cover Crop Productivity, Nitrogen Accumulation, and Weed Suppression

Cereal-legume cover crop mixtures have the potential to combine the unique strengths of the component species while taking advantage of interspecific synergies. However, the relative proportion of each species in the mixture is likely to influence species interactions and entail important tradeoffs in cover crop performance. The objective of this study was to evaluate how the relative proportions of cereal rye (Secale cereale L.) and hairy vetch (Vicia villosa Roth) sown in mixtures influenced cover crop biomass production, winter annual weed suppression, vetch winter survival, and vetch N-2 fixation as measured by the N-15 natural abundance method. Following a replacement series design, treatments consisted of a gradient of seven rye-vetch mixture proportions ranging from 100% vetch to 100% rye. Density and biomass composition in the mixtures were highly correlated with rye and vetch seeding rates, with little evidence of substantial interspecific interference. Total shoot biomass in all mixtures was equal to or greater than that of either monoculture, but no differences were detected in vetch winter survival or the efficiency of N-2 fixation. Changing the proportions of rye and vetch in the mixtures resulted in tradeoffs related to N and weed management goals. Increasing vetch in mixtures led to greater fixed N accumulation but also increased seed costs and reduced winter annual weed suppression. A greater understanding of how rye-vetch mixture proportions influence cover crop performance can support more-informed decision-making regarding cover crop selection and mixture seeding rates.