Questions, answers and more questions about cover crops

By Dusty Sonnenberg, CCA, Ohio Field Leader: a project of the Ohio Soybean Council and soybean checkoff

Just because a farmer has raised cover crops for a few years, it does not mean they have all the answers. Sometimes the experience leads to more questions. The more experience they gain, the more questions they have, but also the more new things they will try.

Hans Kok

Hans Kok, program director of the Conservation Technology Information Center in Indiana led a discussion tackling the FAQs about cover crop management during the latest “Dirt on Soil Health” program.

Some of the common questions Kok encounters include: When is the best time to plant cover crops? When is the best time to terminate the cover crop? What are the best cover crops to plant? What about using wheat or cereal rye as a cover crop? What herbicides should be avoided? What does it cost to grow cover crops? Do cover crops make any money? Are there any value-added cover crops?

“The first question a farmer needs to answer for themselves is why they want to plant a cover crop,” Kok said. “We are only using our farms for about 5 months out of 12 months in the year for corn and soybeans production, which leaves 7 months of unused solar energy. With cover crops we can extend that to around 10 months to capture solar energy and store nutrients.”

There are a number of resources available to aid in cover crop selection. 

“Talking to staff at the Soil and Water Conservation Office, or OSU Extension about what works best in your area is a great place to start,” Kok said. “The Midwest Cover Crops Council (MCCC) offers a Cover Crops Decision Tool (online computer program) that is excellent to help answer a lot of the basic questions in selecting the right cover crop for a farm.”

Planting date is a key factor to establishing a successful cover crop. 

“If a farmer can incorporate wheat in the rotation, that opens a larger window for planting a greater selection of cover crops,” Kok said. “The middle of September is a basic cut-off date that I use for planting most cover crops, other than cereal rye. The rye can be planted later in the fall and still have success.”

Finding alternatives to seed cover crops into a standing grain crop also provides a greater window of opportunity for establishment. 

“Aerial seeding requires rain after the application for it to work,” Kok said. “Large seed cover crops such as peas will not work from a plane reliably. Aerial application generally works fairly well. A high-boy ground rig is another good option. There are some farmers who will inter-seed the cover crops when sidedressing their corn. This typically works best if you are farming north of I-70. You do need to pay attention to herbicide issues if seeding this early.”

How and when to terminate a cover crop is a popular consideration, and it depends largely on the farmer’s comfort level and experience with the cover crop species. 

“We want it to grow as long as it can,” Kok said. “If you are a beginner, it is better that you don’t wait too long. Too many beginners have had a bad experience because they were not able to control the cover crop and had issues planting or took a yield hit.”

Delaying cover crop termination or even planting green provides the greatest soil health benefits. “Legumes need to bloom before termination if you want the nitrogen (N) benefit,” Kok said. “Planting beans into standing cereal rye and then terminating after is becoming more common. Planting corn into cereal rye is not recommended unless you have a lot of experience. The cereal rye takes a lot of the N out of the ground, so you need to have pop-up and 2×2 at planting, and also do an early sidedress to get that N to the young corn if there is a lot of standing cereal rye.”

Using cereal rye has weed control benefits. 

“Resistant waterhemp can be controlled with cereal rye,” Kok said. “Bayer did a study and found a 98% weed control with a cereal rye cover crop. The rye shades out the weeds. It also uses N and takes it away from the weeds. Cereal rye roots exude a chemical that impacts the shallow small-seeded weeds. The chemical does not negatively impact the corn and soy seed which is larger and planted deeper. The way rye hurts corn is by removing the N.”

Residual herbicides can damage cover crops and are another factor to consider. 

“Some cover crops are more sensitive than others,” Kok said. “It depends on the cover crop species, and also the chemistry used. It can also depend on the weather and herbicide breakdown in environment. There are a number of herbicide tables on the Internet that break down the interaction of specific herbicides with cover crops. Depending on the goal, a farmer may need to adapt their herbicide program.”

The economics of cover crops is something that is multifaceted. There are number of variables to consider. 

“The majority of farmers growing cover crops start and try without a subsidy,” Kok said. “Some studies in Illinois show farmers can save $80 to 100 per acre using cover crops versus none. In Ohio an analysis showed a $40 net benefit to growing cover crops. Some of the returns depend on the ability of the crop to be value added. If you can harvest seed, make hay, or graze livestock on it, there are greater returns.”

Kok cautions farmers not to cut corners when purchasing seed. 

“Buy your cover crops from a reliable source,” he said. “Cover crop seed must be cleaned, and needs a seed tag with germination and the percent of weed seed. If you don’t have a tag, you could be buying someone else’s weed problems.”

Kok recommends when starting with cover crops, to first using a lighter seeding rate with rye. “Beginners may want to use a lighter seeding rate, such as 1 bushel per acre,” Kok said. “This makes for easier rye termination, but may not be as effective at weed control. If 2 to 3 bushels per acre of rye are used, it will do a better job at weed control, but can be much harder to terminate with roller, and there is a lot of additional residue to deal with.”

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