Perrone, Sharon2018-09-212018-09-212018-04https://hdl.handle.net/11299/200115University of Minnesota M.S. thesis. April 2018. Major: Applied Plant Sciences. Advisors: Julie Grossman, Emily Hoover. 1 computer file (PDF); vii, 60 pages.Legume cover crops can play a valuable role in maintaining and increasing soil quality and nitrogen availability, but face unique challenges in the Upper Midwest, such as short growing seasons, cold, wet springs, and harsh winters. This study was performed to assess the viability of winter annual legume species in northern climates as a source of nitrogen fertility to a 75-day sweet corn crop (Zea mays convar. saccharata var. rugosa). 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. In 2015-2016, legumes were split into rhizobia inoculated and non-inoculated treatments. In 2016-2017, inoculation treatments were dropped due to no significant findings in biomass production and nodulation between inoculated and non-inoculated treatments. Cover crops were planted in fall 2015 and 2016 at the University of Minnesota Research and Outreach Centers located in Grand Rapids, MN and Lamberton, MN in a randomized complete block design. Total biomass, total nitrogen, and natural 15N abundance were determined for all site years, with nodule mass and number determined in 2015-2016 only. The rye monoculture and biculture produced the most biomass at all site-years ranging from 1.9-3.7 Mg ha-1, while a vetch ecotype (V2) produced as much biomass as the rye monoculture and bicultures in 3 of 4 site-years. Both vetch ecotypes contributed the most nitrogen in 2015-2016, while clover contributed less than rye mono- and bicultures at Grand Rapids in 2016-2017, and there were no significant differences in nitrogen contributions among all treatments in Lamberton in 2016-2017. Hairy vetch ecotype 1 contributed up to 85 kg N ha-1 from aboveground biomass. Data from natural abundance isotopic approaches indicate that 38-103% of vetch tissue N in Grand Rapids and 45-66% of vetch tissue N in Lamberton was derived from atmospheric N fixation, with equal or higher fixation of vetch in biculture at all site-years. Sweet corn yield was equal across all treatments, including a bare ground control. More studies should be performed to enhance N fixation in legume cover crops in the Upper Midwest.enbiological nitrogen fixationcover crophairy vetchlegumesNdfaorganic farmingThesis or Dissertation