Legume cover crops can play a valuable role in maintaining and increasing soil quality and nitrogen availability, but are infrequently grown in the Upper Midwest due to short growing seasons with minimal management windows; cold, wet springs; and harsh winters. This study was performed to assess the viability of winter annual legume species in northern climates as a potential source of nitrogen (N) fertility to a 75-day sweet corn (Zea mays convar. saccharata var. rugosa) cash crop in Lamberton and Grand Rapids, MN in 2016 and 2017. Treatments included medium red clover (Trifolium pratense), two cold-hardy ecotypes of hairy vetch (Vicia villosa Roth), a cereal rye-hairy vetch biculture (Secale cereale L., Vicia villosa Roth), cereal rye as a non-legume control, and a fallow weed-free control. Legumes were split into rhizobia inoculated and non-inoculated treatments. Inoculation had no effect on nodulation, biomass production, or N fixation likely due to competition with endogenous rhizobia strains. The rye monoculture and biculture produced the most biomass at all site-years averaging 7.7 and 7.0 Mg ha−1 respectively while the two vetch ecotypes averaged 4.5 and 3.9 Mg ha−1. Both vetch ecotypes contributed among the most nitrogen in all site-years, contributing up to 211 kg N ha−1 from aboveground biomass. Data from natural abundance isotopic approaches indicate that 75% of vetch tissue N in Grand Rapids and 59% of vetch tissue N in Lamberton was derived from atmospheric N fixation, with equal or higher percent fixation of vetch in biculture at all site-years. More studies should be performed to better understand controls on N fixation of legume cover crops in cold climates.
Bibliographical noteFunding Information:
The authors would like to thank Liz Perkus, Vivian Wauters, Dr. Peyton Ginakes, Dr. Fucui Li, Anne Pfeiffer, Charlotte Thurston, Dan Raskin, Dr. Michelle Dobbratz, Bruna de Bacco Lopes, Rachel Brann, Justin Panka, Emily Swanson, Caitlin Barnhart, Tori Hoeppner, Vick Hoffman, Kaleiilima Holt, and Yordanose Solomone for their field, lab, and data assistance. Additional thanks goes to Matt Galloway, Garett Heineck, and Dr. Andy Petran for their statistical contributions and Doug Brinkman for his growth chamber assistance. Finally, we thank Steve Quiring of the Southwest Research and Outreach Center in Lamberton as well as Keith Mann and Dani Sackett at the North Central Research and Outreach Center in Grand Rapids, in addition to their staff. We gratefully acknowledge the support of the North Central Sustainable Agriculture Research and Education program of USDA project number LNC14-364 and the University of Minnesota’s Forever Green Initiative for funding and the reviewers that graciously volunteered their time to provide this manuscript with meaningful feedback.
- Biological nitrogen fixation
- Hairy vetch
- Organic agriculture
- Red clover