Nitrogen dynamics of hairy vetch (Vicia villosa) and red clover (Trifolium pretense L.) legume cover crops in organicallymanaged agroecosystems in the northern United States

Resumo

Cover crops, non-harvested crops grown between cash crop production, are an agroecological
approach that can increase ecosystem service provisioning. Legume cover crops in particular
are valuable for their contribution of nitrogen (N) via the process of biological nitrogen
fixation. Organic producers in the United States are prohibited from utilizing synthetic nitrogen
fertilizer, and thus employ legume cover crops to provide available N for their non-legume cash
crops. This study evaluates the potential of legume cover crops to contribute to soil N pools.
We assessed four winter annual cover crop treatments at two sites in the state of Minnesota in
the northern United States, including a rye non-legume control (Secale cereal, RYE), red clover
(Trifolium pretense L., CLO), hairy vetch ecotype 1 (Vicia villosa, V1), hairy vetch ecotype
2 (V2), and a hairy vetch – rye bi-culture (V2 MIX). Additional treatments of with-rhizobia inoculation
and without-rhizobia inoculation were imposed to determine the need for inoculation.
Results showed that cover crop legumes contributed from 30-75 kg N ha yr-1, with 50-70% of
plant biomass N derived from the atmosphere via biological nitrogen fixation. An increase in
available soil N was observed following spring cover crop termination. No differences were
observed in nitrogen fixation or nodulation parameters, suggesting that sufficient native soil
rhizobia populations were present to carry out nitrogen fixation.