Cover Crop Selection in Pastures

cows-grazing

There are a number of cover crops species that can be used in monocultures or mixes as forage. Species selection will depend on the specific goals of the producer, the production system (e.g. integrated row crop/livestock, cow-calf, stockers, etc.) as well as the soils and microclimate where the cover crops are going to be grown. When selecting a cover crop as a forage, in addition to considering the benefits on soils erosion, fertility, water retention, and improved weed management, producers should also evaluate the yield potential and quality of the cover crop.

Fall/Winter Planted Cover Crops

In integrated row crop/livestock systems, winter small grains (rye, oats, wheat and triticale) and crimson clover are usually preferred to allow termination of forage production at the optimum time for establishing the subsequent summer crop. These winter annuals are also often overseeded into dormant warm season pastures and will not penalize green up of summer perennial pastures such as bermudagrass. Ryegrass matures late in the spring and provides high yielding and quality forage, but is hard to terminate. It is not generally recommended for double cropping with summer annuals crops. If properly managed, ryegrass is an excellent option to extend the grazing season without interfering with the regrowth of summer perennial pastures. However, if it is underutilized and becomes tall and rank, it can prevent good green up of warm season grasses

Brassicas (tops and bulb types) are very productive cool season crops with good forage quality and that can that can be use at a time when most cool-season grasses are not available. Some of the species include radishes, turnips, rape, and kale. Due to their very low in fiber content that may affect rumen health, brassicas should never comprise more than 75 percent of the forage portion in livestock diets and mineral supplementation will be required. Brassica may cause several animal health disorders if not managed properly (please see Forage Brassicas for Winter Grazing Systems in additional resources).

Spring/Summer Planted Cover Crops

Warm-season annual grasses such as sorghum, sudangrass, sorghum-sudangrass, and pearl millet are highly productive forages species that are frequently used during the “summer slump” to fill yield and quality gaps often found in perennial forage systems during summer months. While many of these species can be no-till planted into killed sods, most perform best in clean tilled situations and as monocultures. Possibly the main limitation to these forages is the increase in cost of production (diesel, seed and N fertilizer) in recent years. In addition, pearl millet and sorghum-sudan can be very hard to maintain in a vegetative state (highest quality) under grazing conditions and nutrient content of these species decreases rapidly as they mature. Also, they have relatively poor curing characteristics due to coarse stems.

Despite its good nutritive value, summer annual grasses may not consistently fulfil the high nutrient requirements of stockers/finishing and dairy cattle. In addition, high level of nitrogen fertilization is usually required to maximize production. Summer annual legumes like cowpea and soybean have the potential to provide forage that is high in protein and fiber digestibility during mid and late summer. In addition, legume species can fix nitrogen from the atmosphere and potentially increase residual soil nitrogen, which can improve forage yields of the successive winter crops, and reduce fertilizer cost. However, when planted as monocultures, legume yields are generally low due to poor regrowth after grazing/harvest. Several summer legumes have shown some compatibility with warm season annual grasses. These include cowpea and soybean. Summer legumes have lower dry matter content compared with annual summer grasses and with a lower plant population of the grass in the forage mix, the overall dry matter per acre is reduced compared to a grass monoculture. Another disadvantage to summer legumes is poor regrowth, which may result in empty spaces that are filled by undesired weeds; consequently, these legumes may be a better complement with one-cut forages like forage sorghum.

Mixtures

When choosing cover crops for forages mixes, select species that are compatible in growth cycle and habit. Usually, more than 3 to 4 species in a mix is not recommended due to the reduce seeding rate that might impact plant establishment. Growing several crop species simultaneously may improve the efficiency of using above-ground and below-ground resources compared to growing them separately. As a result, biomass yield is usually higher than growing any of the component crops alone. It can also reduce the risk of adverse environmental conditions, because one of the forage species may adapt better to the negative conditions.

Herbicide Carryover

Producers looking to graze cover crops or harvest them as hay/silage should consider potential restrictions due to the residual or carry over effect of herbicides from row crop production. Check your herbicide application records before establishing a cover crop for grazing and consult your local Extension and state Pest Management Handbook for herbicide recommendations. In addition, several cover crops species are potentially toxic under certain conditions (see the Plant-based Livestock Disorders page for more information).

Additional Resources
Contributors:

Dr. Matias Aguerre, Assistant Professor, Clemson University; Dr. Lisa Baxter, Assistant Professor and Forage Extension Specialist, University of Georgia; Philip Brown, Grazinglands Specialist, Georgia Natural Resource Conservation Service, Julia Gaskin, Sustainable Agriculture Coordinator – retired, University of Georgia