Crop fields also store carbon dioxide. The question is how much.

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DYSART, Iowa (AP) — When Al Schafbuch let his Iowa fields mow down decades ago and later began planting cover crops, he was trying to save money on fertilizer and reduce erosion. He reaped those benefits and also watched his soil improve into dark, textured organic matter, which he said feels like “chocolate cake.”

Another big benefit that benefits everyone: Tilling less and planting more mulch crops can help farmers store more carbon dioxide, a gas that warms the atmosphere, in the fields. More plants absorb more carbon dioxide, and microbes in the soil expel less carbon dioxide when undisturbed. That can mean money for farmers in the form of carbon dioxide offsets, payments companies that support such farm storage can make to, in theory, offset their emissions elsewhere.

“The more carbon dioxide you take out of the atmosphere with your crops, and the more crops you grow during the year, you offset some of what you waste, the energy that you waste,” explained Shalamar Armstrong, an associate professor of agronomy at Purdue University. “Because you have stored carbon dioxide that would have been emitted into the atmosphere.”

This phenomenon is receiving more attention from policymakers, researchers, and industry professionals. The Agriculture Department announced this week a $300 million investment to study agricultural emissions, including creating a network of researchers to monitor carbon dioxide in the soil. And US Sens. Tina Smith, D-Minnesota, and Todd Young, R-Ind., introduced a bill that Smith said would support research needed “to properly substantiate the storage of carbon dioxide in the earth.”

The USDA announcement and that bill address the difficult question of how to quantify carbon dioxide being stored in the soil. It’s a hurdle to overcome if the burgeoning young market is to avoid the scrutiny and skepticism that markets for carbon credits provoke.

“The scientific element (of carbon credits) has lagged far behind, especially when it comes to things like monitoring, reporting and verification,” said Cristel Zoebisch, deputy director of policy at climate organization Climate 180. “These are huge hurdles. not just for carbon dioxide capture on land, but really for any soil-based carbon removal solution.”

Armstrong has tried to solve that problem. He runs a lab where researchers study how farm management affects the amount of carbon dioxide in the soil in different landscapes. He and others at Purdue have spent more than 40 years investigating soil samples, comparing different tillage styles and cover crops to determine their long-term effects on carbon dioxide storage. Solving it can take years of fieldwork, careful lab chemistry, and a lot of expensive equipment.

The expert hopes that his precise calculations will help farmers make decisions that help them receive valuable incentives for sequestering carbon dioxide, while maintaining their current income.

But other academics worry that even if farmers are paid to store carbon dioxide in the ground, it won’t solve a bigger problem: that carbon dioxide markets often don’t work.

For offsets to be legitimate, they must meet four criteria. They must store carbon dioxide that would otherwise have been emitted, they must be verifiable with data, they must be immediate (planting a tree that could grow in 20 years is not enough) and they must be durable, said John Sterman, a Massachusetts management professor. Institute of Technology.

Better quantifying carbon dioxide sequestration through research could make those tradeoffs more testable, but it doesn’t address other factors. For example, many farmers lease the land they till, and cannot guarantee that the stored carbon dioxide will last for decades if someone else tills the land.

Barbara Haya, director of the Berkeley Carbon Dioxide Trading Project at the University of California, Berkeley, has worked on research that she said shows that carbon dioxide offsets are often overestimated, sometimes by a lot.

“Carbon dioxide trading is a mechanism that has failed miserably for the last 20 years that we really should get away from,” Haya said.

US Rep. Jared Huffman, D-Calif., introduced a bipartisan bill last month to help farmers improve the health of their land, with incentives that didn’t necessarily involve the carbon dioxide market. He noted that farmers in his district have also described the advantages of regenerative practices and that many would be interested in participating in carbon dioxide markets with “firm” accounting systems. But he added that those aspiring to major climate action should not be limited to compensation systems.

“In my opinion, it’s not the antidote,” Huffman said. “I think trade-offs are murky by definition.”

Some growers proceed cautiously.

Brad Wetli, an Indiana farmer who collaborates with Armstrong, has been testing techniques that require less plowing and planting ground cover crops like rye for a few years. He is happy with the current situation in his field – “you feel like you are doing something” to contribute to sustainability, he said – but he continues to weigh his options with possible carbon credit contracts, making calculations and thinking about whether the price will be appropriate, given that many compensation agreements can last several years.

“I’m going to do maybe a plot or two at a time, as I learn more. I look forward to incorporating carbon dioxide or carbon credits into the business more,” she said.

Schafbuch, for his part, is skeptical of carbon credits but would have been in favor of regenerative crops regardless of the initial costs. He said that he was one of the pioneers in including it while his neighbors laughed and said that he “would end up ruined”, but he has proven them wrong.

“I am convinced that if it is done well, everyone can do it,” he said.

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Associated Press writer Joshua Bickel contributed to this report from Fowler, Indiana.

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Melina Walling is on Twitter as @MelinaWalling.

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Associated Press climate and environmental coverage receives support from several private foundations. AP is solely responsible for its content.