Overview of Legume Cover Crops
Commonly used legume cover crops include:
- Winter annuals, such as crimson clover, hairy vetch, field peas, subterranean clover and many others
- Perennials like red clover, white clover and some medics
- Biennials such as sweetclover
- Summer annuals (in colder climates, the winter annuals are often grown in the summer)
Legume cover crops are used to:
- Fix atmospheric nitrogen (N) for use by subsequent crops
- Reduce or prevent erosion
- Produce biomass and add organic matter to the soil
- Attract beneficial insects
Legumes vary widely in their ability to prevent erosion, suppress weeds and add organic matter to the soil. In general, legume cover crops do not scavenge N as well as grasses. If you need a cover crop to take up excess nutrients after manure or fertilizer applications, a grass, a brassica or a mixture is usually a better choice.
Winter-annual legumes, while established in the fall, usually produce most of their biomass and N in spring. Winter-annual legumes must be planted earlier than cereal crops in order to survive the winter in many regions. Depending on your climate, spring management of legumes will often involve balancing early planting of the cash crop with waiting to allow more biomass and N production by the legume.
Perennial or biennial legumes can fit many different niches, as described in greater detail in the individual sections for those cover crops. Sometimes grown for a short period between cash crops, these forage crops also can be used for more than one year and often are harvested for feed during this time. They can be established along with—or overseeded into—other crops such as wheat or oats, then be left to grow after cash crop harvest and used as a forage. Here they are functioning more as a rotation crop than a cover crop, but as such provide many benefits including erosion and weed control, organic matter and N production. They also can break weed, disease and insect cycles.
Summer-annual use of legume crops includes, in colder climates, the use of the winter-annual crops listed above, as well as warm-season legumes such as cowpeas. Grown as summer annuals, these crops produce N and provide ground cover for weed and erosion control, as well as other benefits of growing cover crops. Establishment and management varies widely depending on climate, cropping system and the legume itself. These topics will be covered in the individual sections for each legume.
Legumes are generally lower in carbon and higher in nitrogen than grasses. This lower C:N ratio results in faster breakdown of legume residues. Therefore, the N and other nutrients contained in legume residues are usually released faster than from grasses. Weed control by legume residues may not last as long as for an equivalent amount of grass residue. Legumes do not increase soil organic matter as much as grasses.
Mixtures of legume and grass cover crops combine the benefits of both, including biomass production, N scavenging and additions to the system, as well as weed and erosion control. Some cover crop mixtures are described in the individual cover crop sections.
Berseem Clover (Trifolium alexandrinum) Also called: Egyptian clover Type: summer annual or winter annual legume Roles: suppress weeds, prevent erosion, green manure, chopped forage, grazing Mix with: oats, ryegrass, small grains as nurse crops; as nurse crop for alfalfa See charts, p. 66 to 72, for ranking and management summary. A fast-growing summer annual, berseem […]
Cowpeas (Vigna unguiculata) Also called: southern peas, blackeye peas, crowder peas, cow peas Type: summer annual legume Roles: suppress weeds, N source, build soil, prevent erosion, forage Mix with: sorghum-sudangrass hybrid or foxtail hay-type millet for mulch or plow-down before vegetables; interseeded with corn or sorghum See charts, pp. 66 to 72, for ranking and […]
Crimson Clover (Trifolium incarnatum) Type: winter annual or summer annual legume Roles: N source, soil builder, erosion prevention, reseeding inter-row ground cover, forage Mix with: rye and other cereals, vetches, annual ryegrass, subclover, red clover, black medic See charts for ranking and management summary. With its rapid, robust growth, crimson clover provides early spring nitrogen […]
Field Peas (Pisum sativum subsp. arvense) Also called: Austrian winter peas (black peas), Canadian field peas (spring peas) Type: summer annual and winter annual legume Roles: plow-down N source, weed suppressor, forage Mix with: strong-stemmed wheat, rye, triticale or barley for vertical support See charts, pp. 66 to 72, for ranking and management summary. High […]
Hairy Vetch (Vicia villosa) Type: winter annual or summer annual legume Roles: N source, weed suppressor, topsoil conditioner, reduce erosion Mix with: small grains, field peas, bell beans, crimson clover, buckwheat See charts, p. 66 to 72, for ranking and management summary. Few legumes match hairy vetch for spring residue production or nitrogen contribution. Widely […]
Medics (Medicago spp.) Also called: black medic, burr (or bur) medic, burclover Type: Winter annual or summer annual legume Roles: N source, soil quality builder, weed suppressor, erosion fighter Mix with: Other medics; clovers and grasses; small grains See charts, p. 66 to 72, for ranking and management summary. Once established, few other legumes outperform […]
Red Clover (Trifolium pratense) Also called: medium red clover (multi-cut, early blooming, June clover); mammoth clover (singlecut, late blooming, Michigan red) Type: short-lived perennial, biennial or winter annual legume Roles: N source, soil builder, weed suppressor, insectary crop, forage Mix with: small grains, sweetclover, corn, soybeans, vegetables, grass forages See charts for rankings and management […]
Subterranean Clovers (Trifolium subterraneum, T. yanninicum, T. brachycalcycinum) Also called: Subclover Type: reseeding cool season annual legume Roles: weed and erosion suppressor, N source, living or dying mulch, continuous orchard floor cover, forage Mix with: other clovers and subclovers See charts, p. 66 to 72, for ranking and management summary. Subterranean clovers offer a range […]
Sweet Clovers Yellow sweetclover (Melilotus officinalis) White sweetclover (M. alba) Also called: HUBAM (actually a cultivar of annual white sweetclover) Type: biennial, summer annual or winter annual legume Roles: soil builder, fertility source, subsoil aerator, weed suppressor, erosion preventer Mix with: small grains, red clover See charts, pp. 66 to 72, for ranking and management […]
White Clover (Trifolium repens) Also called: Dutch White, New Zealand White, Ladino Type: long-lived perennial or winter annual legume Roles: living mulch, erosion protection, green manure, beneficial insect attraction Mix with: annual ryegrass, red clover, hard fescue or red fescue See charts for ranking and management summary. White clovers are a top choice for “living […]
Woollypod Vetch (Vicia villosa ssp. dasycarpa) Also called: LANA vetch; also spelled woollypod vetch Cycle: cool-season annual Type: legume Roles: N source, weed suppressor, erosion preventer, add organic matter, attract bees Mix with: other legumes, grasses See charts, p. 66 to 72, for ranking and management summary. Specialty vetches such as woollypod and purple vetch […]