The price of nitrogen (N) fertilizer has increased to the point where it may be cost effective to grow winter legume cover crops as a sole source of nitrogen for a subsequent cotton crop in North Carolina. Establishing these cover crops is critical to the success of this strategy. In order to optimize legume cover crop establishment, cotton producers may have to overseed legumes into cotton that has or will be sprayed with cotton harvest aids, which may interfere with legume germination and growth. A greenhouse experiment was conducted to determine the effects of commonly used cotton harvest aids on legume germination and growth. This was followed by a field study to determine the optimum time to overseed legume cover crops in cotton, to determine the effects of cotton defoliants on legume establishment in the field, and to determine the effects of cover crop species and overseeding timing on cotton growth and yield in a field in which N was not depleted. Cotton defoliants containing thidiazuron plus diuron reduced greenhouse legume germination and growth more than any other cotton harvest aid tested; however, field studies indicate that cover crop germination and cover crop dry weight are not affected by thidiazuron plus diuron. Crimson clover (Trifolium incarnatum L.) and Austrian winter pea (Pisum sativum L.) positively affected cotton yield equally. However, timing of cover crop overseeding played an important role in cover crop germination, accumulated biomass, and lint yield. We observed that overseeding legumes 14 days prior to defoliation resulted in the highest cover crop dry weight and cotton yield.
