Grazing Cover Crops in Late Fall or Winter
2020 Fallby Jeff Mosley
Jeff Mosley, Ph.D., is the MSU Extension Range Management Specialist.
Cover crops are non-cash crops planted to improve a field’s soil health, limit soil erosion, and suppress weeds and other pests. Cover crops also can provide livestock forage. More and more livestock owners in Montana are using cover crops as pasture in late fall or winter, preferably after a hard freeze when the temperature drops below 28F for more than two hours. Cover crops for livestock grazing in late fall or winter are best comprised of simple mixtures containing three to four species. Optimal mixtures include one cereal grain/grass species that comprises 50-70% of the mix, one legume as 20-40% of the mix, and one or two brassicas that comprise 10-30% of the mix. Seed cost is an important consideration when designing a cover crop mixture. Seed costs exceeding $50 per acre typically are not financially sustainable. Cover crops for grazing in late fall or winter in Montana can be planted in either spring (mid-March to mid-May) or late spring/early summer
(mid-May to mid-June). Cover crops planted in late spring/early summer are usually restricted to irrigated fields because most spring-summer rainfall in Montana occurs before July 1.
Cereal Grains and Grasses
Preferred cereals for spring planting are awnless varieties of spring barley, spring wheat, and spring triticale. Preferred cereals and grasses for planting during late spring/early summer are Proso millet, sorghum-sudangrass, or forage corn. Proso millet is better for grazing than foxtail millet (also called Siberian millet) because the roots of Proso millet grow deeper, and in contrast with foxtail millet, Proso millet is not toxic to horses. Proso millet is better than pearl millet because it produces more forage under Montana conditions.
Legumes
Forage field pea is the preferred legume for spring planting. Forage field peas may lose some top growth during freezes, but they can continue growing after temperatures fall as low as 10F. Forage soybean is the preferred legume for planting in late spring/early summer. Late-season frost does not damage soybean plants as long as they are mature (i.e., 95% of pods have turned brown). Chickpea is another cold-tolerant annual legume, but chickpea seed is usually too expensive to use as a cover crop.
Brassicas
Collard and canola are the preferred brassicas for late fall and winter grazing in our state. Both species can be planted either in spring or late spring/early summer. Collard will produce more leaf mass and a larger taproot if planted after the last frost in spring. Radish and turnips are sometimes used for early fall grazing, but they are much less cold-hardy than collard and canola. For example, radish and turnips are usually killed by air temperatures below 25F, while collard often survives down to 0F. Cold-hardy cultivars of canola can withstand temperatures as low as 10F.
Cover Crop Yields and Stocking Rates
Cover crop production varies across Montana. Dryland fields of cover crops produce about 1,000 to 2,000 pounds per acre of dry matter forage in the 11-14 inch annual precipitation zone, versus 3,000 to 4,000 pounds per acre in the 15-18 inch precipitation zone. Irrigated sites typically produce 5,000 pounds or more per acre.
Appropriate stocking rates per acre vary from one to two cows per month (or the equivalent weight of weaned calves, sheep, goats, etc.) in the 11-14 inch annual precipitation zone, three to four cows per month in the 15-18 inch precipitation zone, and five or more cows per month in irrigated fields.
High Stock Density Grazing
The most effective way to graze cover crops is to use High Stock Density Grazing (HSDG). HSDG confines livestock within smaller areas, at higher than normal densities, for brief time periods. Portable electric fence can be used to subdivide cover crop fields into smaller areas (sometimes called paddocks). Grazing periods of one to three days per paddock work best at stock densities of 30,000 pounds or more live-weight of livestock per acre. For example, stock density would be 30,000 pounds live-weight per acre in a 10-acre paddock stocked with 250 cows that average 1,200 pounds live-weight [(250 cows × 1,200 pounds per cow) ÷ 10 acres = 30,000 pounds live-weight per acre]. If the 250 cows remained within the 10-acre paddock for three days, the stocking rate would be 2.5 cows per acre per month [(250 cows × 0.10 months) ÷ 10 acres = 2.5 cows per acre per month].
Cautionary Grazing Practices
The preferred species and mixtures discussed above potentially can cause several livestock disorders, including bloat, nitrate poisoning, prussic acid poisoning, selenium poisoning, goiter, and grass tetany. However, risks are very low when grazing occurs after a hard freeze in late fall or winter. For extra caution: 1) wait to begin grazing until seven days after the field experiences its hard freeze; 2) make sure livestock are not hungry or thirsty when turned into the field; 3) move livestock into the field in the afternoon rather than morning, and 4) provide livestock iodized salt.
Additional Resources
https://landresources.montana.edu/soilfertility/
https://animalrangeextension.montana.edu/forage/
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