With many regions of the U.S. low on forage, demand has driven forage prices up and it’s a good time to think about opportunities for raising cover crops for that purpose, says Scott Wohltman.
No-tillers often raise covers to improve soil health or reduce erosion, but they can also increase productivity when used for grazing, hay or silage.
“Bringing more residue into one’s system can impact soil health in a positive way. It brings protection and generates the opportunity to build soil organic matter,” says the cover crop lead for La Crosse Seed. “But there’s no easier way to make cover crops pay than to use this residue as a source of forage.”
Choosing Forage Covers
Before deciding on a cover crop species, no-tillers should know what service or goal they want it provide, says Wohltman.
Examples could be spring or fall grazing, forage harvesting, silage, or early spring nitrogen availability. They should also consider where covers fit in the rotation and account for potential herbicide interactions.
A cover crop doesn’t have to be a complex multispecies cocktail but should include some plant diversity — mixing grasses (ryegrass, fall cereal rye, millets, sorghum-sudangrass, winter triticale, sudangrass, spring oats and barley, teff, winter barley and wheat), legumes (clovers, sunn hemp, winter hairy vetch and peas) and a limited amount of brassicas (radish, turnip or canola).
Cereals work well for fall and spring forage for many reasons — not just because they produce a lot of biomass, but they lower the TDN (Total Digestible Nutrients) or energy in the ration. That helps prevent heifers and dry cows from getting overweight, Wohltman explains.
When planted early, livestock can make multiple grazing passes in the fall and possibly a pass in spring. Planting cereal grains allows producers to spread manure in the fall before they seed and again after harvest.
Winter rye grows fast in the fall and recovers quickly in the spring. Winter triticale is best for grazing because its large stems make hay welting and silage packing difficult. Winter barley is the most susceptible to winter injury and shouldn’t be planted too late in the season, although it has excellent value as a silage crop and provides 90-95% the nutritional value of corn silage, Wohltman notes.
Spring oats are another good forage option because they usually need only 70-75 days to maximize production and can be harvested early, allowing growers to plant a second crop.
Planting in late July or early August is beneficial for biomass in climates that allow for that, says Wohltman. Producers should harvest oats for silage in the boot stage or for hay in the boot to heading stage.
Annual ryegrass provides good forage: it’s quick to establish, does well in warm soils and tolerates manure well, Wohltman says. In soybean-growing areas, annual ryegrass has shown promise for reducing soybean hematite, but as a cool-season grass it’s intolerant to heat and dry weather. So it typically needs to be planted in the cooler temperatures of spring or fall.
Legumes such as certain clovers and alfalfa in forage mixes can cause bloat, so it’s best to mix grasses with legumes to reduce the risk and avoid turning out hungry animals to fresh, wet legume pastures.
Crimson clover is inexpensive and doesn’t require a lot of seed, but it can cause bloat. Berseem clover is not bloat-forming, is highly nutritious, more salt tolerant than alfalfa or red clover and tolerates wet soils well. The downside is that Berseem clover won’t overwinter in temperatures colder than 10 F, so it’s good for fall forage planted in the spring, Wohltman says.
Winter hairy vetch is a typical green-manure crop and is hardier than most legumes, but it produces hard seeds which can harm livestock, and is a host for soybean cyst nematode and potentially other nematode species as well.
“When cover crops are planted for forage, the herbicide label is the law.”
— Scott Wohltman
Winter peas are hardy to between -5 F to -15 F. They have large seeds and aren’t suited for broadcasting. For winter peas to overwinter, seeding depth is critical. “The deeper, the better, even up to two-and-a-half-inches deep,” says Wohltman.
For spring termination, a close mowing or forage harvest will finish or kill the stand.
Sunn hemp is a warm season plant that grows fast, is tolerant to drought and heat but isn’t winter hardy: frost will terminate the stand. It generates a large amount of biomass with extremely high forage values, being high in digestible carbohydrates and low in fiber.
Summer annuals following a crop like winter wheat take advantage of heat and dry weather when cool-season grasses are dormant. Examples of summer annuals are one-cut forage sorghum, multi-cut sorghum sudangrass and millets.
All of these species produce viable forage, but forage sorghum and sorghum-sudangrass contain a compound that can break down to release prussic acid, basically hydrogen cyanide, and is high in young plants.
“Producers should not graze or cut a summer annual for green chop until plants are at least 18 inches tall,” says Wohltman. “After any kind of stress like drought, livestock should not graze new shoots or green chop for seven to 10 days. A killing frost is another stress that will cause prussic acid levels to rise.”
Nitrogen applications are critical for maximizing forage sorghum, but elevated nitrogen levels from fertilizer or manure usually increases the risk of prussic acid or excess nitrates. Most hydrogen cyanide is lost during curing, so hay and silage are rarely toxic, even if the original forage was, he says.
Summer annuals for silage should be chopped between early dough to mid-dough stage. For producers taking sorghum seed and sudangrass for hay, the highest yields are typically when they are harvested at soft dough, but curing can be difficult and quality is jeopardized when harvesting that late.
“A grower should graze sudangrass after the plant has reached at least 18 to 20 inches tall,” says Wohltman. “Rotate grazing often and use heavy stocking rates. A shorter grazing cycle helps reduce the risk of prussic acid.”
Betting on Brassicas
Wohltman says livestock diets should contain no more than one-third brassicas. “If we get higher than a third, the glucosinolates percentage is so high in some brassicas that it can lead to stomach disorders,” Wohltman says.
“Introduce livestock slowly, avoid turning them out hungry, and always provide plenty of grass or grass hay to compensate for the low fiber in the brassicas. If fall gazing, growers should rotate paddocks often and watch out, because brassicas can be high in nitrates too.”
Tips for Spring
There are a few unique spring management considerations for cover crops, especially if the aim is increasing biomass for forage production.
Number one is increasing the seeding rate, whether seeding small grains, legumes, brassicas or summer annuals.
“If you want more feed, not only will higher seeding rates result in a thicker stand and out-compete weeds, but most species tend to produce more leaves in relation to stems when planted thicker,” says Wohltman.
Growers often need to manage spring residue with a termination and have various options from herbicide application to mechanical methods like rolling, crimping or mowing.
“Utilizing rollers, stalk choppers, and crimpers at milk or soft dough stage usually around 20-24 inches tall, can flatten stems to potentially eliminate a burndown pass,” he says. “If you’re doing this with barley, rolling needs to take place earlier, around mid-bloom.”
Wohltman advises growers to make sure they understand the size and overall biomass of any leftover crop they want to terminate. There are methods of termination that may work for one type of plant but not another, even if they’re the same plant family.
PROS AND CONS. Legumes, such as certain clovers in forage mixes, can cause bloat, so it’s best to mix grasses with legumes to reduce risk. Also, avoid turning out hungry animals to fresh, wet legume pastures, says La Crosse Seed cover crop lead Scott Wohltman. Berseem clover isn’t bloat-forming, is highly nutritious, more salt tolerant than alfalfa or red clover and tolerates wet soils well.
Increased residue can sometimes provide a conduit for pests such as voles or slugs.
“If voles are an issue, I would terminate a high-residue cover crop three or four weeks prior to planting the cash crop,” Wohltman says. “Keep roadsides, ditches and waterways mowed in spring and late fall to decrease the protection they have, especially when vole breeding is heavy and numbers are growing.”
Varying crop rotation disrupts the life cycle for slugs and many other pests. “Plant the cash crop early,” adds Wohltman. “Select hybrids or varieties rated for strong emergence and seedling vigor that’ll get out of the ground fast and get ahead of critters.”
Watch Herbicide Effects
It’s important to understand potential herbicide interactions that could affect cover crop or forage establishment. Residuals herbicides typically provide 8-12 weeks of effective control.
“Residual herbicides can have an impact when planting cover crops in the summer or the fall,” Wohltman says. “Growers should think about cover crops when using residual herbicides on corn, soybean or other cash crops.”
Non-residual herbicides are usually the burndown chemicals used in spring or prior to cash crop plantings and aren’t usually a concern when planting late-season or early-fall cover crops.
Different modes of action also need to be considered because herbicide chemistries act differently in soils and plants. “When cover crops are planted for forage, the herbicide label is the law,” Wohltman says.