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Sixteen winter annual cover crop cultivars were grown in North Carolina to determine total N accumulation, biological N fixation (BNF) potential, and compatibility with a roller‐crimper‐terminated organic corn ( Zea mays L.) production system. Cover crops and termination dates were tested in a stripped block design. Treatments included hairy vetch ( Vicia villosa Roth), common vetch ( Vicia sativa L.), crimson clover ( Trifolium incarnatum L.), Austrian winter pea ( Pisum sativum L.), berseem clover ( Trifolium alexandrinum L.), subterranean clover ( Trifolium subterraneum L.), narrow leaf lupin ( Lupinus angustifolius L.), and Balansa clover ( Trifolium michelianum Savi.), as well as bicultures of rye ( Secale cereale L.), hairy vetch, and Austrian winter pea. Roller‐crimper termination occurred in mid‐April, early May, and mid‐May. Total biomass, N concentration, and C/N ratios were determined for cover crops at all roll times and natural 15 N abundance at the optimal kill date. Hairy vetch and crimson clover monocultures had the greatest overall biomass in 2009, and bicultures the greatest biomass in 2010. Crimson clover successfully terminated in late April, hairy vetch and Austrian winter pea in mid‐May, and berseem clover and common vetch in late May. All cover crops except lupin and subterranean clover derived between 70 and 100% of their N from the atmosphere. Corn response to cover crop mulches was significantly affected by the time of rolling, with poor stands resulting from competition with insufficiently terminated mulches. Crimson, Balansa, and subterranean clover mulches resulted in poor corn yields despite relatively high levels of total N. The highest corn yields were achieved in hairy vetch and rye plus hairy vetch bicultures.