ON A FARM in north-central Indiana, Brent Bible raises 5,000 acres of corn and soybeans that go into producing ethanol fuel, food additives, and seeds. In Napa Valley, California, Kristin Belair picks the best grapes from 50 acres of vineyards to create high-end cabernet sauvignon and sauvignon blanc wines. Both are part of a growing number of "carbon farmers" who are reducing planet-warming greenhouse gases by taking better care of the soil that sustains their farms. That means making changes like plowing fields less often, covering soil with composted mulch and year-round cover crops, and turning drainage ditches into rows of trees.

Now Congress is considering legislation that would make these green practices eligible for a growing international carbon-trading marketplace that would also reward farmers with cash.

This morning, Bible is scheduled to testify at a Capitol Hill hearing before the Senate Agriculture Committee, which is considering the carbon-farming legislation. Introduced by senators Mike Braun (R-Indiana) and Debbie Stabenow (D-Michigan), the bill sets up the US Department of Agriculture to certify independent consultants for farms that want to participate in carbon trading, and inspectors to verify that the farmers make the changes they promise.

The bill doesn’t set aside any taxpayer money to pay the farmers to change their practices or for the carbon inspectors themselves. Those funds would come through commissions on the sale of future credits or from the farmers’ own pockets.

As more big corporations and governments promise to go carbon-neutral, many are relying on carbon-emissions trading as a way to meet their goals. When a company buys carbon offsets, it funds projects elsewhere to help reduce greenhouse gas emissions, such as planting trees in Indonesia or installing giant machines inside California dairies that suck up the methane produced by burping and farting cows and turn it into a usable biofuel. What the offsets don’t do is force their buyer to change their own operations.

Even many supporters of offsets say they are only an acceptable tool once companies have done everything else they can to pollute less, such as tightening up manufacturing processes, cutting down on office heating, or making delivery trucks run on cleaner fuels. Critics say offsets don’t always work as planned, because not all of these projects actually pan out. There’s a difference between an airline that promises to cut emissions by switching to cleaner fuel (good for immediately reducing greenhouse gases) and one that buys offsets for planting trees (not as good) that might be cut down a few years later.

In 2018, the latest year for which data is available, nature-based solutions such as tree planting and capturing methane from dairy farms accounted for a reduction of 100 million metric tons of carbon dioxide globally, according to a 2019 report by the nonprofit group Forest Trends. That reflects about $300 million in purchased offsets.

Under the bill being discussed today, technically called the Growing Climate Solutions Act of 2020, farmers and growers would get credits for finding ways to reduce carbon emissions on their land. This would then be verified independently, and they would be assigned credits that could be sold on the market. Agricultural credits are currently selling for $13 to $17 per ton of carbon, according to a Senate committee staff member.

US farmers like Bible have a big role to play in reducing agricultural emissions. Farming techniques contribute about 24 percent of global greenhouse gas emissions; these include practices such as the use of nitrogen fertilizers and plowing fields after the growing season, which aerates the soil and allows carbon to reach the atmosphere. (In the US, agricultural emissions are only about 10 percent of the total US carbon budget, according to EPA figures. But that’s just because the rest of the US economy produces so much greenhouse gas from other sources, like traffic and residential energy use.)

Since there’s currently no federal program to encourage carbon farming, Bible and Belair have been making changes on their own. Bible says his operation has been employing soil sequestration techniques for many years, such as planting cover crops in the spaces between rows to protect soil and switching to no-till farming. That means his fields aren’t plowed over at the end of the season, which keeps the carbon in the soil. He sees the benefit of carbon sequestration and carbon trading as one of dollars and cents. "If I am incentivized to perform a function and produce a product, and the ability to reduce our carbon footprint is a product we can manufacture, then we are going to do that," says Bible. "Agriculture has proved it can do it very well."

For Belair, carbon farming is part of a spectrum of sustainable practices at Honig Vineyard and Winery that includes the use of renewable solar power, organic farming techniques to reduce the use of chemical pesticides, and encouraging pollinators like bees, an insect emblem that is found on every bottle of Honig wine. These practices, which are also known as regenerative agriculture, "have been around since the 1970s," says Belair, Honig’s winemaker for the past two decades. "It’s not new, it’s just that industrial farming doesn’t allow for these practices, and many soils are terribly depleted. Restoring soil health will sequester a lot of things that have been lost, including carbon and nitrogen."

Honig is one of 15 vineyards that have put together carbon sequestration plans with the help of the Napa County Resource Conservation District, which hopes to make the fertile valley’s lucrative wine industry carbon-neutral in the coming years. Belair is aware that changing agricultural practices isn’t going to reverse global climate change overnight, but it does signal a shift in how farmers and growers view their land. "We have to reduce our greenhouse gas emissions by a lot," Belair says. "It’s going to take a multipronged system to do that."

Some experts believe that carbon farming faces too many obstacles to make a dent in atmospheric carbon emissions. In a 2018 paper, UC Berkeley biogeochemistry professor Ronald Amundson wrote that it’s too hard to accurately measure how much carbon actually gets stored in the soil, mainly because of seasonal variation. He notes other social and cultural obstacles, such as the fact that 40 percent of US cropland is leased by renters who don’t have much incentive to invest in long-term soil conservation measures.

Still, some experts say there are good reasons for taking care of the soil, in addition to keeping carbon emissions locked in the earth. "When you manage land for optimal health of the soil, you increase productivity of the land, you increase its resilience to extreme events like rainfall or wind erosion, you increase its water holding capacity and resilience to drought," says Tim Filley, professor of earth, atmosphere and planetary sciences at Purdue University.

Filley and his colleagues are working on new techniques to better measure how much carbon is contained in soil, a process that until recently has required farmers to send dozens of earth samples to a laboratory for analysis. New handheld sensors are starting to become available, as well as computer models that estimate the exchange of gases from soil to the atmosphere that take into account the ups and downs of seasonal variability over many years.

Filley has met with members of the Senate committee working on the US carbon-farming legislation. He hopes that the new bill will encourage more farmers to protect their soil and perhaps make a bit of a dent in climate change. "How do you verify that you are increasing carbon in the soil?" Filley says. "That’s where the marketplace and science can come together to make great strides."