Sustainable Practices for Vegetable Production in the South
Dr. Mary Peet, NCSU
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Annual ryegrass (sometimes called Italian ryegrass) has moderate cold tolerance, high shade tolerance, and moderate to high drought tolerance. Ryegrass provides a good spring hay or grazing crop before turning under. It has a branch type leafy growth, but tillers profusely. Widely adapted and very quick to establish, it can become a weed because it volunteers readily. It does not fix nitrogen and may actually tie up nitrogen temporarily when turned under. The seeding rate is 20 to 25 pounds per acre. To ensure overwintering, ryegrass should be planted after June but at least 40 days before the first expected frost. Grasses should have three to four leaves before freezing weather occurs. It can be overseeded into a well established vegetable crop if weeds are controlled beforehand and if moisture is not a limiting factor. Overseeding into peppers, tomatoes, or eggplant should be done after the early bloom to full bloom stage. In sweet corn, ryegrass can be overseeded after the final cultivation and before the corn is 12 to 15 inches tall.

Austrian winter pea (legume)

Austrian winter pea has moderate cold tolerance, moderate to high nitrogen fixation capability, low shade tolerance and low drought tolerance. It is very quick to establish, prefers a soil pH of 5.5 to 7.5, and is widely adapted. The seeding rate is 40 to 90 pounds per acre and it should be seeded in October in the South. Austrian winter pea is a host for nematodes and is susceptible to winter crown rot diseases, especially when grown for more than one year in the same field.

Black medic (legume)

Black medic has moderate to high cold tolerance, moderate nitrogen fixation capability, and low shade and drought tolerance. Although moderately fast to establish, it does not tolerate traffic. Black medic prefers a soil pH of 7.0 to 7.5 but will grow in most soil types. The seeding rate is 10 to 15 pounds per acre and the seed is rather expensive. While often planted in the fall, black medic can also be grown as a summer annual that will reseed. Plants need to be well established to overwinter, however.

Crimson clover (legume)

Crimson clover is also usually grown in the fall but can be grown as a summer annual. It has good cold tolerance, good nitrogen fixation capability, moderate drought tolerance and moderate to high shade tolerance. Crimson clover prefers a soil pH of 5.7 to 6.4 and does not grow well in wet or alkaline soil.

Crimson clover should be planted at a rate of 10 to 20 pounds peracre approximately 40 days before the first killing frost. Crimson clover is very quick to establish and will overwinter if it has not reached the bud/early bloom stage before the start of cold weather. The ideal time to turn it under is by early bloom before the flower color starts to fade. Biomass accumulation is greatest from late vegetative to late bloom stages. Total N was greater in the early seed set plants because of their greater biomass but N was released more quickly from late bloom material.

Mowing will also kill the crop, but this must be done no later than full bloom to prevent reseeding. If reseeding is desired, however, either planting of the cash crop must be delayed or it must be planted into killed strips of clover, while adjacent strips are allowed to reseed. In dry years, reseeding may provide a better stand than planting since seeds will break dormancy on a gradual basis. Therefore, some are likely to germinate with adequate soil moisture present. This works best when the cash crop is to be planted late enough that the seeds are mature.

Crimson clover contributed 60 to 90 pounds N per acre with about 35 percent of that N being recovered by the following crop (corn, in this case).

Hairy vetch (legume)

Hairy vetch grown in combination with winter rye is a very widely used and frequently recommended cover crop for vegetables. Usually grown in the winter, it can also be grown as a summer annual. It has excellent cold tolerance, moderate to high nitrogen fixing capabilities and moderate shade and drought tolerance. Hairy vetch prefers soil pH of 6.0 to 7.0 but is tolerant of a fairly wide range of soil conditions. The seeding rate is 25 to 40 pounds per acre and it can reseed itself. Although hairy vetch establishes quickly, it should be planted 40 days before the first killing frost in order to make enough growth to overwinter (usually 3 to 5 inches).

Dr. Abdul-Baki demonstrates the potential for biomass production by hairy vetch.

Spring oat (grass)

Oats need well drained soils and are prone to lodging and disease in poorly drained heavy clays. Typically, 96 pounds per acre are seeded early enough to allow plants to reach 6 to 12 inches tall before growth is slowed by low temperatures (30 to 40 days of growth after emergence). Spring oats will grow vigorously in the fall if seeded early enough. When grown as described above, the winter-killed crop will still provide good cover.

Subterranean clover

Subterranean clover is moderately tolerant of acid soils, has low shade tolerance and reseeds well. It is a low-growing, dense legume which produces seed below the soil surface. Because of its reseeding ability, it has been used as a living mulch. In New Jersey, subterranean clover seed matures and the plant dies back in mid-June. The succeeding crop is established by early September. Experiments comparing various management systems of subterranean clover with conventional pre-emergence herbicide use showed that plots with subterranean clover yielded as much as plots where weeds were controlled by herbicides. Mowing versus not mowing had no effect on sweet corn yield. In squash, highest yields were found when the clover was strip-tilled or killed versus mowing or not mowing although using pre-emergence herbicides produced higher yields. In beans and tomatoes, weed control and yields were similar to yields with subterranean clover and pre-emergence herbicides.

Winter rye (grass)

Winter rye has high cold tolerance, moderate to high shade and drought tolerance and is fast to establish. It prefers a slightly acid soil and sandy loam to loam soil type. The seeding rate is 60 to 120 pounds per acre. The roots of rye release chemicals that inhibit the germination of small seeded broadleaf weeds such as redroot pigweed, purslane and common ragweed. Rye grows very tall and plant residues have a high C:N ratio. Because of its cold tolerance, it is the best choice for late fall plantings, providing excellent winter erosion control and removing excess soil nutrients.

Winter wheat and barley (grass)

Winter wheat and barley cover crops are used in the same way as rye although they should be seeded earlier in the fall because they are not as cold tolerant. Barley prefers well drained, non-acid soils and is very drought tolerant. Both barley and winter wheat are somewhat less vigorous and easier to incorporate in the spring than rye but also need more time to produce the same amount of biomass. The seeding rate is 60 to 120 pounds per acre.