Choosing a cover crop to protect Oklahoma farmland from erosion is fairly easy. Cereal grains, mostly wheat or rye, will hold soil in place until producers can get cotton, corn, or grain sorghum up in the spring.

To the east, where producers look for summer and winter grazing, options to improve soil organic matter, and to help manage weeds, farmers have more options.

“Erosion control is the main reason Oklahoma farmers plant cover crops in our row crop areas,” says Oklahoma State University Cropping System Specialist Josh Lofton, Stillwater.

“But cover crop use in Oklahoma is multi-faceted. Ten years ago, a lot of growers were staunchly against using cover crops. Then a lot started planting cover for erosion control.

“Our western soils are very fragile to wind erosion when they get dry. And we have periodic dry spells. Down in our cotton area and out in our high plains where we plant more row crops, erosion control is the primary reason to plant cover.

“When you move to other parts of the state, we have more mixed uses. In those areas, producers appreciate the value of cover crops that can be grazed while maintaining a sustainable system.”

Lofton says having something on the land that provides high-quality forage while doing something positive for soils is a big incentive.

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Weed management

Managing weeds offers another incentive, he says. “The closer we get to the eastern side of the state, near Arkansas growers sometimes use cover crops to aid problematic weed management, especially in systems that integrate soybeans, which do not produce a lot of residue between crops.

“Producers add cover crops to get residue on the ground, which aids water management and also helps mitigate some weed management issues.”

Biomass production is better in the eastern parts of Oklahoma, Lofton says.

“The farther west we go, winter covers don't typically produce enough biomass to improve soil health. Winters are cold and harsh, and that's typically when we go through another dry spell. If we don't get much snow melt, when the ground warms up, cover crops don't grow a lot.

“And producers have to terminate so early that they lose a lot of winter cover. They don’t need a lot of biomass just to hold the ground in place,” Lofton says.

Biomass

Summer cover crops to the east and farther south, where producers are planting for grazing purposes, can create a good amount of biomass.

“We use the NRCS biomass recommendation—  around two tons per acre, 4,000 pounds — for EQIP ground, before grazing,” Lofton says. “Some summer systems and eastern operations can produce that much. Western systems, especially during the winter, can't get 4,000 pounds in the time they have to grow them.”

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Lofton says it’s not impossible to get a decent amount of biomass on Western winter cover crops, but it’s much less likely.

“Producers in the western row crop areas would need good snow melt or good rainfall and a warm winter, an unusual year. More often than not, they probably produce below the NRCS value by the end of the year.”

Best covers

Options for row crops and erosion control, Lofton says, are mostly cereal grains. Wheat is probably the most widely used.

“Because Oklahoma is such a wheat state, producers sometimes get a bit shaky about planting rye. We see wheat, maybe some oats if producers have a failed wheat crop and want a cover they can graze or cut for hay.

“If they just want ground cover, they can plant a spring oat. “We've had some try barley.”

Into the summer, growers might turn to things like millets and sorghum — Sudans and BMR sorghums. “Even if they prefer a mix, those options could be a big component of it. They might sprinkle in other things but most of it will be either a small grain cereal or some sort of grass crop.”

Where the climate and soils are more favorable, the options are more varied.

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“In those areas, they plant more legumes and some forbs,” Lofton says. “Some folks have added okra, which offers nice summer grazing. Cattle will seek out okra.”

Other options

He says other options include sunflowers, which cattle also like.

He adds that legumes make up part of some cover crop mixes. “We have some cow peas and mung beans, which are very well adapted for our region.’”

Lofton worked in Louisiana for several years and says farmers there liked vetch and clovers. “Oklahoma growers I've talked to don't favor vetch and clovers as much as they do other, more large-seeded legumes like beans and peas.

“We've also had a big push the last two years on sun hemp in our summer cover systems. Producers like sun hemp because of the nitrogen it can bring into the system.”

He says sun hemp is an interesting plant. “It's fairly well adapted for the region. It likes these hot summers.”

Lofton says sun hemp seed is “supposed to be sterile, so you don't have the potential of weed carryover. A lot of our growers say cattle like it. It’s a tall crop, so it competes well planted with millets or sorghums.”

Caution

He cautions farmers to be wary of trying too many unproven species.

“Watch out, you never know what could be the next kudzu, the next eastern red cedar, or something like that. We see probably two or three new cover crops come out every year.”

Other options for mixes include brassicas. “Be aware that  a little further north some brassicas will winter kill early. Things like daikon radishes that are prevalent in other parts of the country may not be suited here. Dry conditions paired with cold and fluctuating temperatures seem to winter kill those very early.”

Lofton says a solid stand of radishes may eventually mean no cover remaining. “If those are intermixed with a cereal, you might have pockets with no cover, but radishes do help spur nutrient cycling. They have some value.”

 Purple top turnips, he says, might be a better option.

“A lot of folks have grown those in deer plots, so they know how to manage them.”

Some producers also have integrated canola, a winter hardy brassica, into winter cover crop systems. “Some have grown it as a crop and are familiar with managing it.

“Canola provides a lot of the same benefits as other brassicas. Seed may be a little more prevalent because we still grow it as a crop. However, if a brassica makes it through winter, it is hard to terminate, compared to grasses or legumes. Method of termination is also a factor.”

Lofton says terminating brassicas chemically, once they've hardened off over the winter and moving towards reproductive growth, is challenging.”

Flexibility

Lofton says flexibility is a key aspect of cover crops in row crop or livestock enterprises. “We never know what Southwest summers will bring.”

He says growers who decide never to plant a cover crop or to plant one every year could miss the point.  “If they use it as a tool, like it should be used in our production systems, a cover crop can provide flexibility and add residue to the soil.”

He explains that a producer coming out of a bean crop with little residue might plant a cover after harvest to augment residue. Also, if conditions turn dry after a corn, sorghum, or wheat crop that produced a good amount of biomass, opting out of planting a cover might be a good option.

“A cover crop adds flexibility to production systems and adds residue when we need it and can help conserve moisture that might not otherwise be available when it’s time to plant the next cash crop.”