Chapter 16

The Use of Cover Crops to Manage Soil

Cover Crops and Their Uses

Cover crops have multiple uses, providing several opportunities for inclusion in crop rotation. Cover crops may be used as green manures, catch crops, living mulches, residue mulches, and forages.

Green Manures

Cover crops are grown to protect and/or enrich the soil. When turned into the soil, a cover crop may also be called a green manure. The crop is grown in a period of fallow between two cash crops. Green manuring adds organic matter, nitrogen, and other key nutrients as part of sustainable soil management plan. Organic farmers consider green manures to be an essential part of the farm ecosystem.

Catch Crops

Cover or catch crops are used for reducing nutrient leaching, transferring nitrogen to the next main crop, increasing biodiversity, and maintaining or improving soil structure. This is both an economic issue for the farm and an environmental issue. Catch crops have been shown to have the most marked effects on the availability and loss of soil inorganic nitrogen and sulfur. Catch crops can be grown as annuals, biennials, or perennials, and can include a wide range of plant species, including cereals, legumes, brassicas, and grasses. In general, legume cover crops do not scavenge nitrogen as well as grasses. A grass or brassica or a mixture is usually a better choice for taking up excess nutrients.

Living Mulches

Living mulches are an extension of cover crops used to decrease soil erosion, suppress weeds, improve soil structure, and nutrient cycling, and in the case of legumes, supply nitrogen to a grain crop. Unlike cover crops that are killed before planting the crop, living mulches co-exist with the cash crops during the growing season and continue to grow after the crop is harvested. The key to successfully integrating living mulch into a cropping system is proper management to ensure the living mulches complement the cash crop. Living mulches do not need to be reseeded each year. They can be chosen and managed to minimize competition with the main cash crop yet maximize competition with weeds.

Residue Mulches

High-residue cover cropping is an adaptation of conservation tillage in which a high-biomass cover crop is grown during the winter and is rolled or cut down prior to no-till or strip-till planting in spring. Winter cereals typically used as high-residue cover crops include rye, black oats, wheat, or triticale. A high-residue cover cropping system can enhance the normal benefits of conservation tillage (e.g., reduced erosion, improved infiltration, better nutrient cycling, etc.) because of the increased biomass of the cover crop.

Forages

The use of cover crops in a cropping rotation or as an integrated livestock-cropping system has become a popular option for farmers. Cover crops may provide opportunities to use cropped land for grazing livestock or to produce a harvested feed source. Livestock grazing of cover crops can further recycle nutrients back into the soil. Harvested cover crops for hay, haylage, and silage; when harvested at the correct time, can provide a nutrient-rich winter feed.

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