Cover crops boost organic matter

With interest in soil health growing across the food-production spectrum, finding ways to help soil improve is more critical than ever. Building soil organic matter — and thus soil carbon — is key, and growing cover crops is central to that process. Three cover crop growers shared what practices have helped build organic matter in their soils.

In southern North Dakota’s dry, rugged terrain just west of the Missouri River, near the town of New Salem, Rocky Bateman stands out for increasing soil organic matter levels to 4.5% from 1% on marginal land. Bateman and his wife, Nancy Jo, began no-tilling some 25 years ago. They also started raising diverse crops, and 10 years ago began growing cover crops. With the addition of the cover crops came faster growth in soil organic matter.

An educational series for farmers who want to take their skills to the next level. Check out more Farm School content HERE.

Build Organic Matter 101: Set a Goal

Bateman set a goal of building a farming system mimicking the native prairie. “Native prairie and all of its diverse plants represent the ideal soil profile,” he says.

To promote diversity in cash crops, he rotates crop types between cool- and warm-season grasses and cool- and warm-season broadleaves. His full-season cover crops also include warm- and cool-season grasses and broadleaves.

Near Forrest, Illinois, corn and soybean grower Marcus Maier chooses cereal rye as his cover crop. He tried fall- planting oats and radishes, but found they winter-kill if planted late, reducing their cover crop benefits. “Cereal rye will overwinter even with no noticeable stand in the fall,” he says. “The rye will still come through in the spring.”

As a result of growing the rye cover crop, combined with leaving corn residue on the soil surface and practicing both no-till and minimum-till, Maier has seen levels of soil organic matter climb to as high as 5% in some fields from between 1% and 2%.

Increases in soil organic matter have also come from growing cover crops on Michael Willis’ farm near King City, Missouri, where he no-till farms in partnership with his father, Ron, and brother, Matthew. 

Cereal rye was their first cover crop in 2012, but they soon switched to triticale. The Willises grow their own cover crop seed and found that triticale consistently yields more seed than rye.

After growing cover crops for five years, they saw soil organic matter levels increase by a half of a percentage point.

Build Organic Matter 201: Add Cover Crops to the Rotation

On Bateman’s 1,800 acres in North Dakota, his diverse cash crops have included corn, soybeans, flax, sun-flowers, and spring wheat, depending on the year. 

He formerly planted a diverse cover crop in early fall after harvesting wheat or flax, but limited moisture hindered cover crop growth.

To get more above- and belowground biomass in the cover crop, Bateman switched to growing a full-season, multispecies cover crop planted by the first of June. He puts cover crops in fields with soil health issues, planting 150 to 250 acres annually.

In midsummer, he cuts the cover crop for hay, harvesting 3 to 3.5 tons per acre of forage. The cover crop regrows to provide early-fall grazing. “From my perspective, the aboveground biomass is secondary in importance to the biomass in the roots,” he says. “The root system feeds the soil biology, which leads to increases in soil organic matter.”

He sources a diverse cover crop seed mix from a regional seed supplier, paying $25 to $35 an acre for the seed. He seeds the mix with a no-till drill.

In Illinois, where Maier grows corn and soybeans on 520 acres, drilling in the cereal rye cover crop behind harvested corn has proven effective. “I seed the rye over the top of the cornstalks in mid- to late October,” he says. “Drilling the seed ensures good seed-to-soil contact, giving a consistently good stand of rye. In the spring, the rye will be  6 to 8 inches tall, when I normally terminate it.”

Maier sources the cover seed from a local seed supplier and pays 35¢ a pound plus the cost of hiring a custom applicator. He seeds the rye at a rate of 50 pounds per acre, which yields a stand that helps with weed suppression.

Willis grows primarily corn and soybeans on 1,100 acres, along with 60 acres of triticale for cover crop seed. He plants the cover crop after harvesting corn, seeding most of the triticale cover by early to mid-October. He plants triticale for seed after soybeans, seed-ing the triticale by mid- to late October.

Broadcasting is his seeding method of choice. “We spread the cover crop seed with a fertilizer cart, which is cheaper than a drill and is able to cover more ground quickly,” he says.

The Willises try to time the broadcasting of the seed right before a rain. “The rain helps to work the seed into the soil,” says Willis.

However, if seeding the cover crop is delayed until late October, they drill in the seed to give the cover crop the advantage of a more “foolproof” seeding method. 

When broadcasting, they seed at a rate of 100 to 150 pounds to the acre. When drilling, they decrease the rate to 50 to 60 pounds.

Build Organic Matter 301: Diversity

Multispecies cover crop mixes offer the advantage of providing more diverse food sources for soil biology. But the diverse mixes sometimes produce less biomass than small-grain cover crops while also costing more, says Mark Licht, Iowa State University Extension cropping systems specialist. “Legumes, for instance, take longer to establish and often don’t over-winter well,” he notes.

Legume and brassica species that may be more likely to persist through Iowa’s winter include red clover, hairy vetch, winter camelina, and winter canola. “Though winter canola can be a little hard to terminate,” he says.

Species aside, it’s the living roots in the soil that hold the key to cover crops’ benefits. “When the plant is actively growing, it takes up nutrients that would otherwise leach away or run off,” says Licht. “Then, as the cover crop decomposes, those nutrients be-come available for the next crop. The living roots also provide soil pores that enhance the root growth of subsequent crops.

“Living roots promote a living soil system that increases the building of soil organic matter, particularly in a no-till system,” 

he says. “Tillage infuses oxygen into the soil, which burns organic matter. Natural porosity does permit oxygen to enter the soil, but it doesn’t infuse the soil with oxygen like tillage does. A no-till system has a better chance of building soil organic matter than does a tillage system.”

For the Willises, building organic matter and strengthening soil structure has greatly reduced soil erosion, produced more uniform yields across the farm, and reduced their need for fertilizer and lime.

In North Dakota, Bateman’s diverse, no-till cover cropping system has “restored the soil profile and thus the wa-ter cycle and the soil’s ability to retain moisture,” he says. “The soils are more resilient, and our operation is more drought-proof. In the last 24 years, we’ve tripled our wheat and corn yields. Some of that increase is due to improved genetics, but a lot also has to do with improved soil health, soil carbon, and organic matter.

“We need to restore the soil to its native state so that it stays healthy and productive forever,” he adds. 

“Native prairie soil is a healthy ecosystem, which is highly dependent upon diversity. Adding cover crops to a cropping system speeds up the healing process.”

5 Tips for Cover Crops That Promote Soil Health

1. Mimic the native prairie with diverse plants.
2. Combine cover crops with no-till and minimum till.
3. Use a multispecies cover crop.
4. Find a seeding method that ensures good seed-to-soil contact and a good stand.
5. Strengthen soil structure with living roots.
   
   

Check out more Farm School content HERE.

This educational editorial series is sponsored by: