Soybean producer using cover crops

(Photo: Joclyn Bushman/Iowa Soybean Association)

What we learned about cover crops in 2022

February 9, 2023 | Kriss Nelson

Iowa Soybean Association (ISA) Senior Field Services Program Manager Scott Nelson is looking through data from the 2022 growing season as he prepares to assist producers with their cover crop management practices in 2023.

It was a year of highs and lows, considering weather conditions that varied throughout the state.

Termination issues

Last spring, Nelson says there were issues with terminating cover crops mainly due to conditions not conducive to a glyphosate burndown.

“Glyphosate is the most common herbicide used to terminate cover crops. It works slowly in cloudy, cold weather allowing the cover crop to grow and get large,” he says. “It will eventually die, but the kill is slower.”

Cover crop termination was an issue for West Branch farmer Jake Pedersen last spring.

Pedersen farms alongside his father and brother, raising 2,200 acres of corn and soybeans. They have been using cereal rye to cover 100% of their acres for the past three years after introducing cover crops into their operation eight years ago.

The cool, wet conditions deterred Pedersen from a timely glyphosate application, causing his rye in one field to grow to 18 inches before he could terminate, ultimately resulting in a 40-bushel yield drag in corn.

Pedersen learned from the 2022 crop year; if weather conditions allow, he’ll spray sooner in the season to terminate the cereal rye. He’s more comfortable with cereal rye growing eight- to 10 inches in height before terminating.

If producers are in the same predicament this spring, Nelson urges them to consider a tank mix to partner with their glyphosate.

“Cover crops add a whole level of management, and you need to be flexible." Pedersen says. "The more times you try, learn and share your experiences, the more you can hopefully minimize mistakes.”

Cover crop blends

To help producers diversify their cover crop acres, ISA conservation and regional agronomists research various cover crop blends to develop systems that raise cash crop yields.

“Scientific literature shows various species of cover crops help to improve yield, but there have been little to no on-farm characterizations in Iowa,” says Nelson. “We seeded micro plots across the state with different species and blends to see what survives over the winter.”

Pedersen is working with Nelson to help introduce camelina, hoping it will thrive and add some diversity to their cereal rye cover crop.

“We are doing our best to replicate the whole gamut of what nature provides and reap the benefits while still trying to manage any impact on our cash crop,” Pedersen says.

Frost-seeding cover crops

Producers in abnormally dry areas that may not have had a successful fall seeding of their cover crops could still have an opportunity to benefit from cover crops.

Nelson and the team at ISA have been looking into the potential value of frost-seeding cover crops in late March or early April.

“There could be time for a cover crop of oats, annual rye or cereal rye to grow to a good height before planting soybeans,” Nelson says. “This could give you an advantage for improving soil health and creating root channels for summer rain infiltration or weed control from the biomass.”

Having a cover crop prevalent in fields during the spring can also help sequester any nitrogen that would otherwise be lost to production.

Nelson says cover crops in a soybean-corn rotation can be especially valuable.

“Planting cover crops ahead of growing soybeans is valuable, especially with drought conditions because there is likely nitrogen left over from the corn,” he says. “If we can sequester nitrogen with oats or some species of grass ahead of the soybeans, the nitrogen will be stabilized in the early spring and available for soybeans later in the season when it needs it. Frost-seeding is a good way to maintain your nitrogen investment from 2022.”

Weed control

Cover crops continue to play an essential role in inhibiting herbicide-resistant weeds in soybeans, Nelson says.

Using the biomass left over after terminating cover crops requires proper management. Nelson recommends allowing the cover crop to grow eight- to 12 inches tall in the spring before termination.

“In my opinion, this growth is the safest, surest way you can get good biomass and root channels to infiltrate rain,” he says.

Nitrogen stabilization

Cover crops can work as a nitrogen stabilizer as the growing plants can soak up the available nitrogen from early-season manure applications — especially if manure is applied to warmer soils — and preserve it over the winter.

“We cover our soybean stubble with manure,” says Pedersen. “Our goal is to apply manure and seed the rye to ensure we are trapping some of those nutrients by keeping something growing in place.”

His soybean crop is reaping the benefits of the combination of manure application and cover crops. Eighteen months after a manure application — and after a season of growing corn — he’s seen yield bumps in his soybean crops.

“We had our highest soybean average in 2021 and beat that in 2022,” Pedersen says.

He’s working with Nelson to determine if cover crops are sequestering leftover nitrogen from the manure that the corn crop didn’t utilize and releasing it to the soybean crops when the plants need it.

Not only can cover crops help sequester nitrates, they may also help alleviate a large problem associated with manure applications: compaction.

“Cover crops can break up the compaction to improve soil tilth and increase water infiltration,” Nelson says. “We are learning more about how important cover crops are in manure applications.”

Cover crop trial opportunities

The ISA team at the Research Center for Farming Innovation (RCFI) is ready to work with farmers on in-field research trials.

“We know soybeans work in a cover crops system. We know we have better soil health, increased water quality and more nitrogen recycled, but sometimes we don’t see a yield advantage,” Nelson says.

The RCFI team wants to help farmers determine the potential.

“Many farmers aren’t concerned, however, because of the profit advantage from the weed control angle. We think there should be a yield advantage, and we would like to work with farmers to understand and realize this potential.”