Farm Progress

Prairie Farmer’s cover crop series continues with a review of what Illinois farmers, agronomists and cover crop experts have learned through trial and error. Plus: Their advice for new cover croppers.

Jill Loehr, Associate Editor, Prairie Farmer

November 6, 2017

7 Min Read
COVER CROP FOR N: Crimson clover is a good nitrogen-producing cover crop, says Nathan Johanning, University of Illinois Extension, but it’s not as winter-hardy as cereal rye, and needs to be established early in the fall for the best winter survivability.

“The one thing I can’t say enough about cover crops is grow and learn at your own pace,” says Nathan Johanning, University of Illinois Extension. “Don’t jump in with both feet and try do everything the first year.”

Establishment. Termination. Species mix. The part-art-and-part-science management requirements can seem overwhelming to new cover croppers, but more and more farmers are fighting through the learning curve.

“Growers are finding a fit for cover crops, in some capacity,” notes Johanning, who lives near Murphysboro. “Some are using something as simple as cereal rye, and others are planting larger mixes.”

What has the ag industry learned about cover crops in Illinois? Johanning, agronomists and cover croppers weigh in.

1. Keep crops simple. “Cereal rye is the standard cover crop with good biomass, and it has a fairly forgiving planting window,” Johanning says, adding that farmers in southern Illinois can plant cereal rye into mid-November. “It’s pretty reliable across variable conditions and a good fit in a lot of areas,” he says.

2. Cover crops suppress hard-to-control weeds. Cereal rye produces chemicals that suppress tough-to-control weeds like marestail, Johanning says, and outcompetes waterhemp by shading and building a residue barrier. Karen Corrigan, McGillicuddy Corrigan Agronomics, says she’s surprised more farmers who struggle with waterhemp or marestail don’t consider a cereal rye cover crop.

3. Know pros and cons: drilling, spreading, flying. “For cereal rye, drilling is by far the most effective and consistent,” Johanning says. Seed-to-soil contact and soil moisture help the cover crops start strong. Surface application, like with a fertilizer spreader, works well in some situations, but you need rainfall shortly after planting. Winterkill cover crops, like turnips and radishes, benefit from early planting via aerial application, but cost per acre increases by $15 to $20, and the stand can be inconsistent around field edges.

4. Beware of residual impact, especially in dry years. Later-season residual herbicides may impact sensitive cover crops, like rapeseed and brassicas, Johanning says, especially when rain hasn’t diluted the herbicide. University of Missouri weed scientist Kevin Bradley studied the potential impact of several corn and soybean herbicide programs on cover crop stands and found that the tillage radish was the most sensitive species. “We’re trying to get a better handle on this,” Johanning adds.

5. Make sure corn has enough N at planting. Cereal rye, or any grass cover crop that overwinters, uses nitrogen early in the season, Johanning explains. Galva farmer and cover cropper Brian Corkill says several farmers learn that lesson the hard way. “Lots of guys think the antagonism between cereal rye and corn is what causes the issues with yield in corn, but nine times out of 10, there’s not enough N to offset the nitrogen needed to break down the residue,” Corkill says.

Johanning says 50 pounds of nitrogen or a starter fertilizer can go a long way to help corn following a grass cover crop. “We haven’t lost any nutrients, but it’s tied up in the rye when we need it,” he adds.

6. Time cover crop terminations before corn carefully. “The worst-case scenario is a half-dead cover crop that’s too wet ahead of corn,” Johanning says. Terminating two weeks prior to corn planting, when the cover crop is manageable, gives you the benefit of spring cover from the cover crop while allowing enough time for the cover crop to die before planting.

Keep an eye on the forecast, Corrigan advises. Glyphosate needs warmer weather to translocate into the plants.

7. Go green in soybeans. To get the most out of your cover crop and to avoid planting into a dead mat, many cover croppers have found it’s ideal to plant soybeans into growing cover crops. Corkill terminates his cereal rye the day before planting or up to a week after planting. “This spring, the cereal rye was pushing 7 feet tall, and we sprayed it with a quart of glyphosate and killed it,” he says. “Planting into an established cover crop is a lot easier to manage.”

8. Get good advice on seeding rates. Cover crop species time of year, and planting method all impact cover crop seeding rates, Johanning says.

Matt Boucher, who sells custom blends of cover crop seed and farms near Dwight, says a farmer planting cover crops ahead of beans whose main goal is weed control may drill 40 to 60 pounds an acre of cereal rye. “If we need to broadcast that on, then add 10% to that. If we fly it on, then we need to add roughly 20%,” he says. “Every situation is different — it depends on the time of the year, every farm is different and every field is different.”

Johanning says planting a pound or two per acre of radishes and rapeseed can go a long way. The Midwest Cover Crop Decision Tool is a good place to find the best cover crop based on your location, cash crop, planting date, harvest date and cover crop goals, he adds.

Boucher recommends finding a trusted cover crop seed dealer who will help you design the right mix and rate based on your objectives.

9. Cover attracts insects, so scout early and often. Early season pests, like cutworms and armyworms, may be drawn to cover crops like cereal rye. Johanning recommends scouting during the first few weeks and applying an insecticide treatment as needed. “Year to year, it’s not that bad,” he notes. “But it can always be that one year.”

10. Start small in the beginning. “You don’t need a huge 15-way cover crop mix,” Johanning says. “Even just one species, like cereal rye, is a good place to start. Things get more complex with broadleaves, legumes and grasses — work your way into it.”

Corrigan recommends farmers start with 10 to 20 acres before soybeans to gain some experience and to figure out their cover crop goals. “Define your mission; then you’ll know your mix,” she says.

Still not sure about where to start? There are farmers who have been there, done that. Corrigan says social media platforms, including Facebook and Twitter, offer several groups and users who ask questions and share advice. “Talk to someone who has had success and failures,” she says. “The best information is going to be talking to someone who has been through it.”

What is still unknown about cover crops
Benton farmer and Certified Crop Adviser Kelly Robertson will be the first to tell you he’s not against cover crops. He uses a fertilizer spreader to plant oats or wheat on his highly erodible ground. But when the cover crop mix includes turnips, radishes and a several other species, and the cost increases to $50 or $60 per acre, Robertson starts to get concerned.

“If someone wants to sell me on seed corn or a herbicide program, they have numbers and replicated plots,” he says. “With cover crops, I haven’t seen anything like that. There’s no research that says if I plant X and terminate at Y, I get Z.”

Farmers facing low corn prices need to understand the return on investment for every input decision they make, he adds. The anecdotal success stories — like improved soil health and reduced soil erosion — are great, but for the additional cost, Robertson wants numbers before investing in multiple cover crop species. “There has to be research to show that this is better than this,” he says.

Johanning says hard and fast return-on-investment numbers on cover crops is an ongoing obstacle. “I’m not sure how many times we’ve sat around a table and tried to come up with numbers,” he says. “We all know what we’ve seen, but trying to quantify it is something we’re still trying to nail down season to season.”

Editor's note: Check out Prairie Farmer’s firsthand cover crop reports from Illinois farmers who have “been there, done that” with cover crops:

• Brian Corkill: Where do we go from here?

• Chad Bell: Keep cover crops simple

• Matt Boucher: What works and what doesn’t

About the Author(s)

Jill Loehr

Associate Editor, Prairie Farmer, Loehr

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