MIDLANDS - Cover crops were once a mainstay of agriculture for a variety of purposes. Lately, they have been primarily thought of as conservative measures to prevent erosion. Actually, cover crops can be used for nutrient recovery and fixation, nematode and disease suppression, and nutrient generation as well as erosion prevention. I will discuss each of these uses and suggest some cover crops suitable for use in the home garden.
Unused fertilizer elements particularly nitrogen, sulfur, magnesium, and potash will move with water below the root zone of most garden crops during the season (leaching). With the winter rains, these elements will continue to move eventually being tied up with soil elements or getting into ground water. They would no longer be available for crop production. Many cover crops have deeper root systems than our garden crops and can reach down into the lower soil depths and 'pull' these nutrients up and incorporate them into plant matter. This is referred to as biological fixation. As long as they are in the plant matter, they cannot leach through the soil. When the cover crop is terminated and plowed back into the soil, these 'lost' elements are slowly released as the plant material decays and can be used by crops. Small grains such as rye, wheat, or oats are good choices for use in the winter, while buckwheat is a good choice for this purpose in the summer.
A number of cover crops produce either while growing or upon breakdown chemicals that will kill or reduce the growth of many plant nematodes and other disease organisms. Home gardeners in general have few resources with which to fight nematodes and soil-borne diseases, so suppressive cover crops such as rye or black oats (winter) or velvetbean or sudan/sorghum hybrids (summer) may help if you have nematode or disease problems.
You can use cover crops to produce nitrogen; such a cover crop is called a 'green manure'. At one time, this was a very important source of fertilizer nitrogen that was generated on the farm. Recently, this practice has been supplanted by cheaper sources of synthetic nitrogen. Legumes (plants in the bean family) have the ability to take gaseous nitrogen out of the air and turn into useable 'fertilizer' nitrogen. The nitrogen then becomes available to animals that may eat the plants or to other plants when the legume is plowed into the soil. Some legumes can generate over 90 lbs of nitrogen per acre. This nitrogen is available slowly over a long period of time and is an excellent source of plant food. Many legumes are available to use in the winter (crimson or red clovers, arrowleaf clovers, hairy, common and white vetches, Austrian field peas and winterpeas) or in the summer (cowpeas, soybeans, and velvetbean).
Now is the time to plant clovers and vetches in the midlands of South Carolina. If you choose to use a small grain such as rye, wheat, or oats, you can plant those later into November. Warm season grasses and legumes such as millet, sudan/sorghum hybrids, cowpeas, soybeans or velvetbeans should be planted in the late spring into the summer to get good germination and growth. Your local extension office has information about using cover crops in your garden.