Winter Cover Crops And Green Manure Strategies

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By Anita B. Stone Winter cover crop strategies refer to cover crops scheduled into a crop rotation plan. Organic farming relies on soil health and cycling of nutrients through the soil using natural processes. Cover crops are usually a legume planted to keep soil from leaching, eroding, and weeding over to improve the conditions associated with sustainable agriculture. In agriculture, a green manure is a type of cover crop grown primarily to add nutrients and organic matter to the soil. Typically, green manure crops are grown solely to be turned under, while green and soft to be incorporated into the soil for improvement.

So the question commonly asked includes the reason for using green manures. First they increase the percentage of organic matter in the soil, thus improving water retention and aeration. The root systems of some green manures grow deep in the soil and typically bring up nutrients that might otherwise be unavailable to certain crops. Third, normal cover crops suppress weeds and prevent soil erosion and compaction. When allowed to flower, some crops create a habitat for beneficial insects.

Cover crops used for these purposes are of two classes: those that gather nitrogen from the air and add it to the soil, and those that cannot do this but merely protect the surface and conserve what nutrients are already present. For example, soon after the corn crop harvest, many farmers plant soybeans as a green manure crop. The soybeans restore nitrogen to the soil for the next season. It is common to see these in tobacco fields once harvested. Crimson clover (sow an ounce to 200 square feet), winter vetch (an ounce to about 60 square feet), and Canada field peas (an ounce to about 40 square feet) are the most suitable nitrogen-gathering crops for most landscapes.

Crops of the other type include buckwheat (one ounce to about 60 square feet), ryegrass, winter rye, barley and oats (one ounce to 30 square feet). A good cover crop combination is buckwheat, crimson clover, rye and winter vetch sown all at once in mid July, either on an empty landscape or between rows of late vegetables. The first frost will kill the buckwheat and perhaps the crimson clover won’t live over winter, but the rye and vetch will; they will continue growing in spring until dug or plowed under. Winter cover crops such as oats and rye have been used for many years. Crops such as sweet clover, crimson clover and hairy vetch perform the vital function of fertilization, with the addition of animal manures when used. Berseem, a Mediterranean clover, is a cool, fast growing crop and resembles alfalfa. Berseem is being used in the United States as an annual winter legume. Most feed and supply stores can provide you with this seed crop.

Green manuring can be historically traced to the fallow cycle of crop rotation, which was used to permit soils to rest for a time. This process works, but is incredibly superseded by a crop rotation plan, producing more cash crops and providing future cash crops.

The knowledge that cover crops protect bare soil against erosion is critical. Green manures come from behind and improve soil fertility. Because a cover crop is primarily added to the soil, it becomes a green manure. So cover crops and green manures are interchangeable terms, perhaps even working symbiotically towards the same end result to improve and protect the soil while allowing crop growth and additional nutritional value.

Certain strategies depend on the benefits for the farm. Due to the additional fixed nitrogen added to the system, soybeans have become one of the main green manures used in mulch farming practices along with alfalfa, which also fixes large amounts of nitrogen over the years. Crops that grow late in the season can still obtain nutrition that would be lost without cover crops. Ideally, select the benefit of the cover crop, and then decide what to plant. For example, legume cover crops will provide nitrogen but they are not hard at work with weeds. If you select a rotational plan with cash crops, you can select the cover crop required to work well with that particular crop. Also, take into consideration seed cost, winter hardiness, and how the crop acts to soil conditions, and tillage equipment.

Cover crop strategies prioritize how the cover crop fits into a crop rotation plan.

There are several strategies for the use of cover crops. First, consider whether a fallow crop requires taking land out of cash crop production for all or part of a season. Secondly, plan for winter crops that are sown in late summer or fall and remain in place until spring. Third, use methods to smother crops that are grown during spring, summer or fall between crops.

Emphatically, a major goal of cover cropping is to avoid bare soil between cash crop plantings. This protects the soil and inhales sunlight, producing topnotch soil quality. The field lends itself to more traffic, reduces compaction and potential for animal feed production.

Fallow cover crops rank high in rotation benefits because the soil has a resting period from cultivation. This, in turn, lessens diseases and adds biomass to the soil to maintain its structure and supply of organic carbon and nitrogen. Although fallow crops can be expensive in terms of lost crop production because they are grown instead of a cash crop, the bottom line serves the land well.

Fallow crops certainly excel over a mass production of weeds that take over and invade the land.

One of the best ways  to get a jump on the winter cover crop season is to inter-seed, or under-sow a cover crop into a standing cash crop. If you did not get around to a very late vegetable harvest, and it is too late to put down winter rye to protect the soil, a solution is to inter-seed with a choice selection, an advantage that some winter protection gets established and the soil is not left bare.

Inter-seeding requires good soil and seed contact, ample water, and weed control so the cover crop has a chance to establish. Timing is essential. Sowing requires delay to minimize competition with crops, but early enough so the cover crop can survive with the vegetable crop. Following the last cultivation, inter-seed a cover crop. If your crop includes peppers, tomatoes, kale, or cabbage it is suggested to sow winter cover crops.

Small, slow growing crops are not recommended for inter-seeding. Carrots and onions will suffer in the field. Hardy crops like winter squash and sweet corn are more likely to produce well. If the cash crop is winter squash, inter-seed cover crops prior to running vines. Perennial or annual ryegrass are excellent manures for winter squash. Low growing red clover is a short-lived perennial used for soil acidity or poor drainage. It can be oversown into corn.

Whatever strategy is used, prioritize the cash crops along with the green manures for quality soil to produce the highest yield on the farm. Keeping a journal is a beneficial method to determine which cover crops, green manures and cash crops yield the best interaction strategy for top production.