The use of legumes as a winter cover crop and green manure for subsequent summer annual crops in the southeastern U.S. has been limited due to relatively inexpensive sources of nitrogen. However, the cost of synthetic nitrogen has nearly tripled in the last 11 years, stimulating growers to reconsider the use of legumes as a cost-effective source of nitrogen. Selecting an appropriate legume species, timing of cover crop termination, and timing of summer crop planting can be adjusted to supply total season nitrogen needs of cotton (Gossypium hirsutum L.) in North Carolina. Crimson clover (Trifolium incarnatum L.) and hairy vetch (Vicia villosa Roth) were used as green manures in cotton as a sole source of nitrogen in field experiments conducted in North Carolina during 2010 and 2011. The highest cotton yield and biomass were noted when cover crops were terminated by a single broadcast herbicide application at 10 days before cotton planting. Lint yield of cotton following crimson clover and hairy vetch equaled lint yield of cotton without cover crops plus 70 kg N ha-1 of liquid urea ammonium nitrate. Net return of the legume cover crop/cotton system equaled net return of the cotton liquid nitrogen system and ranged from 1,240 to 1,650 $ ha-1.
