Biomass Production and Nitrogen Accumulation By Hairy Vetch-Cereal Rye Mixtures: A Meta-Analysis.

Cover crop mixtures are increasingly being employed to provision multiple agro-ecosystem services. However, there is inconsistent evidence in the literature on the biomass production and nitrogen (N) accumulation of individual cover crops species as compared to when grown in mixture. We conducted a meta-analysis using results from 20 studies to examine biomass and N content of hairy vetch (Vicia villosa Roth)-cereal rye (Secale cereale L.) mixtures compared to monocultures. Results indicated that the relative productivity of hairy vetch-cereal rye mixtures compared to component monocultures depends on soil type, previous crop, seeding proportion, and growing degree days (GDD). Overall, hairy vetch-cereal rye mixtures produced 60, 25, and 7% more biomass when compared to hairy vetch, cereal rye, and the max monocultures, respectively. ‘Max monoculture’ refers to the monoculture with the greatest yields in terms of biomass (cereal rye in 71% of the cases) and N content (hairy vetch in 88% of the cases). Hairy vetch-cereal rye mixtures accumulated 1.6 times more N than cereal rye monocultures. When the sown proportion of hairy vetch in the mixture exceeded 48%, mixtures also accumulated relatively more N than the max monoculture. A more consistent positive response of mixtures on biomass and N content were found under N-limiting conditions (on coarse-textured soils and following corn harvest). While the biomass and N content of mixtures relative to hairy vetch monocultures decreased with increasing GDD, the biomass and N content of mixtures relative to cereal rye monocultures increased. This suggests slower growth of hairy vetch in the fall and early spring followed by rapid hairy vetch growth in the late spring. The superior biomass productivity and N accumulation by hairy vetch-cereal rye mixtures likely enhanced agroecosystem services associated with cover crops, making them a potential tool for sustainable agricultural systems.