Winter Annual Cover Crops
Winter annual cover crops have been used in rotation with summer crops for many years in North Carolina, but now there are some interesting new applications of this practice. Early experiments date from the 1940s and show several important benefits of planting winter annual cover crops, chief among them erosion control, addition of nitrogen (N) to the soil for use by a subsequent crop, removal of N from the soil to prevent nutrient loading, buildup of soil organic matter, and buildup of residue that acts as a mulch for water conservation or retention.
Generally, winter cover crops are planted in early fall and allowed to grow over the winter until early spring, when their growth is terminated by plowing or herbicide treatment. In conservation tillage systems, the residue from the cover crop is not plowed under after the herbicide treatment and remains on the surface as mulch (Figure 1A). A newly developed alternative for certified organic farms that provides similar residue conservation without herbicides involves cover crop termination using a roller-crimper (Figure 1B).
Winter annual cover crops can be either legumes or cereals. The legumes best adapted to North Carolina soil and climatic conditions are crimson clover, hairy vetch, Austrian winter pea, and Cahaba white vetch. Recent trials have also included lupines, berseem clover, subterranean clover, and other legumes. Cereals or small grains that are best for North Carolina are rye, wheat, barley, triticale, and oats. Descriptions of many potential cover crop species can be found in the US Department of Agriculture publication Managing Cover Crops Profitably.