Called cover crops, they top the list of tasks U.S. farmers are told will build healthy soil, help the environment and fight climate change.
Yet after years of incentives and encouragement, Midwest farmers planted cover crops on only about 7% of their land in 2021.
That percentage has increased over the years but remains small in part because even as farmers receive extra payments and can see numerous benefits from cover crops, they remain wary. Many worry the practice will hurt their bottom line — and a study last year indicates they could be right.
Researchers who used satellite data to examine over 90,000 fields in six Corn Belt states found cover crops can reduce yields of cash crops — the bushels per acre. The smaller the yield, the less money farmers make.
"I don't want to abandon it, but as far as just going whole-hog with planting cover crops, that's a tough thing for me to do," said Illinois farmer Doug Downs, who plants cover crops only on a sliver of his land in a relatively flat region of east-central Illinois.
Cover crops are plants grown on farmland that otherwise would be bare. While crops like corn and soybeans are growing or soon after harvest, farmers can sow species such as rye or red clover that will grow through winter and into spring. They stabilize soil, reduce fertilizer runoff, store carbon in plant roots and potentially add nutrients to the dirt.
The practice is key to government efforts to sequester carbon in farmland to help reduce climate change, since there's general agreement planting the right off-season crops can pull carbon from the air and keep it underground in plant roots.
The U.S. Department of Agriculture promotes cover crops through several programs, starting with $44 million in payments during the 2023 fiscal year from the agency's Natural Resources Conservation Service for over 4,700 contracts to plant them on more than 344,000 hectares. Additional funding was available for conservation practices, including cover crops, through the Inflation Reduction Act. Another program provided $100 million in extra benefits through federal crop insurance coverage to farmers who plant cover crops.
There's heightened interest in cover crops for carbon storage, though the effectiveness depends on the soil, plant variety, temperature and other factors.
The Natural Resources Defense Council has put so much stock in cover crops that it recently launched a social media campaign with Nick Offerman, featuring the Parks and Recreation TV show actor buried in dirt while promoting the practice. The environmental group has encouraged Congress to give farmers more lucrative financial incentives to plant the crops.
The NRDC points to studies that have found cover crops don't necessarily reduce cash crop yields and can boost growth. And Lara Bryant, the group's deputy director of water and agriculture, notes that while the overall percentage of farmers planting cover crops is small, acreage increased by 50% to about 5% of U.S. cropland from 2012 to 2017, the most recent year USDA data is available.
"We have a long way to go but we've come a long way in a short amount of time," Bryant said.
However, the 2022 satellite study found yields declined by an average of 5.5% on corn fields where cover crops were used for three or more years. For soybean fields, the decline was 3.5%. The declines varied depending on factors such as cover crop type, soil moisture and soil quality.
"I was surprised it was so negative," said David Lobell, a Stanford University agricultural ecologist who worked on the study published in the journal Global Change Biology with researchers from Illinois and North Carolina. "We rechecked everything and were a little bit surprised."
The study found that rye, the most frequently used cover crop, is especially prone to reducing yields, Lobell said. Rye is less expensive than many cover crops and grows well in many kinds of soil.
The study examined farm fields in Illinois, Iowa, Indiana, Michigan, Missouri and Ohio, using satellite images. Lobell said details from an individual field are less precise than on-the-ground study, but by examining thousands of fields, researchers can reach accurate conclusions.
The researchers said farmers need more technical help choosing and maintaining cover crops as well as more government or food industry payments to offset potential yield losses. The federal government and at least 22 states provide financial incentives to farmers — and food companies such as General Mills and PepsiCo pay more to farmers who plant cover crops.
Terry Cosby, chief of the USDA's Natural Resources Conservation Service, acknowledged establishing effective cover crops can take time and some experimenting but said farmers who stick with them should see significant benefits. He noted the Biden administration's allocation of $19.5 billion for climate smart programs over five years and that federal, state and university outreach services can provide technical advice.
"It's going to take some trials and errors," Cosby said. "It might fail but over the long term ... it has been proven that you can be very successful with some type of cover crop."
Downs, the Illinois farmer, has tried to incorporate cover crops into some of his operations, especially to control weeds. But he says it hasn't been easy.
In 2019, Downs planted rye in one field but didn't plant it on an identical field across a road. The spring was wet and the rye field was so soggy, he couldn't get in for weeks to kill the cover crop and plant his soybeans, resulting in a smaller crop.
"Growing a cover crop cost me $250 an acre, and I spent $50 an acre doing it," Downs said.
Farmers don't typically harvest and sell cover crops; they frequently use herbicides to kill them before planting their principle crop.
Less than 32 kilometers away, fourth-generation farmer Curt Elmore has been "dabbling" in cover crops for a decade, planting varieties like oats and rye on parts of the 809 hectares he farms.
Elmore seeds cover crops by plane before harvesting his cash crop, but cover crop growth has been spotty, not worth the cost.
Elmore said he'll keep trying, but it seems that in his area of Illinois, it will take more payments from governments or companies to convince many additional farmers to take up the practice.
"If this is an imperative, then somebody is going to have to pay for it," he said.
Joe McClure, Iowa Soybean Association research director, said the Stanford study largely confirms his organization's research, though he thought the university researchers should do field study to verify their satellite-based analysis.
McClure said more more financial support would help farmers avoid having to choose between planting cover crops and losing money.
J. Arbuckle, a professor in Iowa State University's sustainable agriculture program, said it's important to be open with farmers about possible yield reductions and how they can be mitigated over longer periods, such as six or seven years.
Even then, Arbuckle said, it can be hard to convince farmers to give cover crops a try because, despite the significant environmental benefits, a small drop in cash crop yield can mean a big cost.
"Even a one bushel hit, if you're talking about a bushel an acre over a thousand acres, that's a lot of money," he said.