The Biden administration and a growing coalition of lawmakers have promoted the planting of carbon-trapping crops as a key strategy in the fight to control climate-warming emissions.

But farmers across the country’s Upper Midwestern Corn Belt are only planting a small fraction of their land with these plants—known as cover crops—despite tens of millions of dollars in federal and state funding encouraging them to do so.

In a new analysis published Wednesday, the Environmental Working Group (EWG), an environmental research and advocacy nonprofit, found that acreage planted in cover crops remained exceedingly small and had leveled off across the Corn Belt after a bump upwards from 2015 to 2017. In 2019, the latest year EWG analyzed, out of 68 million acres of corn and soybean, only 3.2 million acres were planted with cover crops, which are usually planted between cash crops over the winter.

The group tracked satellite data from Illinois, Indiana, Iowa and Minnesota, where monocultures of corn and soy have led to soil erosion and fertilizer pollution that has stoked harmful algal blooms. Each of these states has set goals to cut fertilizer pollution, in part by using cover crops, which prevent fertilizer from running off into waterways.

“We thought, by tracking the persistence and emergence of these cover crop plantings, we could track how effective we are at meeting those goals,” said Soren Rundquist, EWG’s director of spatial analysis. “They’re nowhere close.”

That shortcoming also suggests that cover crops may not be a particularly effective climate solution, either.

“It’s doubtful that they’ll be a silver bullet for carbon reductions,” Rundquist said.

A Bill With Backing from an Unlikely Alliance

A study published in Science Advances in 2018 found that planting cover crops has the potential to hold carbon in the soil or offset emissions, but only if it is scaled-up across hundreds of millions of acres. To put any meaningful dent in U.S. emissions, EWG’s analysis found, current “cover crop acres would have to increase fourteen-fold to get close to the number of acres needed to achieve a miniscule reduction.”

The findings come as cover crops, once an obscure concept far removed from the conversations of Washington politicians, have become central to legislation aimed at helping farmers control carbon emissions. Last week, the Senate passed the Growing Climate Solutions Act, designed to help farmers participate in carbon offset markets.

The bill, which passed with bipartisan support, would help set up a third-party system to measure and verify how much carbon farmers are storing—through practices including cover cropping—so that they can sell it in the form of credits to polluters looking to offset their carbon emissions.  Already, farmers have started to sell a small number of credits to companies through private markets. The legislation would create a network of consultants and technical experts, overseen by the U.S. Department of Agriculture, to help farmers better assess their greenhouse gas reductions.

The bill, which now heads to the House of Representatives where it faces a tougher road, has the support of an unlikely alliance of environmental groups, agricultural corporations and the farm lobby, which has long fought against climate action. 

But the EWG analysis adds to growing  concerns on the part of some environmental groups that voluntary carbon markets like the one the legislation envisions will only allow polluters off the hook and fail to reduce overall emissions. One main concern is that the methods for verifying the extent and permanence of carbon storage gained from cover crops are still very much undeveloped.

“The offsets industry is an infant industry and we clearly need better tools to measure and verify the benefits of different conservation practices,” said Scott Faber, EWG’s senior vice president for government affairs. “There are many reasons to adopt cover crops, including improved water quality and making farms more resilient. Cover crops are likely sequestering some carbon. Right now we lack the tools to know how much.”

Unlike carbon locked away in fossil formations for millions of years, carbon in the soil tends to be released in much shorter time frames. The EWG findings suggest that the durability of soil carbon is also a question, mostly because farmers can change practices from year to year.

The analysis found that farmers who planted acres in cover crops in a given year, failed to do so in subsequent years.

“The persistence of land that’s covered every other year over that period from [2015 to 2019] gets substantially smaller,” Rundquist said. “That’s telling us that the planting of these cover crops is pretty ephemeral. It flickers on and off. The scale needed to produce substantial changes for clean water or carbon—we’re not even close.”