Thurston, Charlotte2019-05-132019-05-132019-03https://hdl.handle.net/11299/202895University of Minnesota M.S. thesis. March 2019. Major: Applied Plant Sciences. Advisor: Julie Grossman. 1 computer file (PDF); v, 99 pages.We investigated the effect of Upper Midwest winter temperatures on nitrogen contributions of winter annual legume crops via productivity and symbiotic nitrogen fixation (SNF). Projects included: 1) a controlled environment study of growth, nodulation, and SNF in crimson clover (Trifolium incarnatum), Austrian winter pea (Pisum sativum), and hairy vetch (Vicia villosa), and 2) a high tunnel evaluation of four cover crop mixes for productivity, nodulation, and SNF. High tunnel treatments included: a) crimson clover monoculture (T. incarnatum), b) red clover monoculture (Trifolium pratense), c) Austrian winter pea/winter rye biculture (Pisum sativum and Secale cereale), and c) hairy vetch/tillage radish/winter rye mix (V. villosa, Raphanus sativus, and S. cereale). Legume biomass, nodulation, and SNF were limited below 10°C. In high tunnels, lowest biomass and nodulation occurred in mid-winter and lowest SNF in early spring. Delayed spring recovery of SNF suggested that later winter annual cover crop termination could increase nitrogen contributions.encover cropshigh tunnelslegumesSymbiotic nitrogen fixationtemperaturewinter annualThesis or Dissertation