Maryland farmer Trey Hill pulled in a healthy haul of corn last fall and then immediately planted rye, turnips, clover and other species, which are now spreading a lush green carpet over the soil. While his grandfather, who started the family farm along the Chesapeake Bay, always planted in the spring in a clean field, in Hill’s approach to farming, “you never want to see the ground.”
As the winter cover crops grow, they will feed microbes and improve the soil’s health, which Hill believes will eventually translate into higher yields of the crops that provide his income: corn, soybean and wheat.
But just as importantly, they will pull down carbon dioxide from the atmosphere and store it in the ground. Hill is at the cutting edge of what many hope will provide not just a more nature-friendly way of farming, but a powerful new climate solution.
In early 2020, he became the first seller in a privately run farmer-focused marketplace that paid him $115,000 for practices that, over the past few years, had sequestered just over 8,000 tons of carbon in the soil. The money came from corporations and individuals who want to offset carbon dioxide produced by their activities. Hill used the proceeds to buy equipment he hopes will allow him to squirrel away even more of the planet-warming gas.
If farmers throughout the world adopted similar “regenerative” methods, experts estimate they could sequester a sizable chunk of the world’s carbon emissions. The idea has been endorsed by soil scientists, a slew of food industry giants and, recently, President Biden.
But some doubt that farmed soils can reliably store carbon long enough to make a difference for the climate — or that changes in soil carbon can be accurately yet affordably measured. Others worry voluntary measures such as soil sequestration could make a polluting food and agriculture industry appear environmentally friendly while forestalling stronger climate action.
Researchers and companies are now racing to reduce the scientific uncertainties and win over skeptics.
Many scientists are confident that farming can be adapted to build carbon into soils, said Deborah Bossio, a soil scientist at the Nature Conservancy, an environmental organization. “We know how to do it,” she said.
Agriculture has done a masterful job of feeding the world’s burgeoning population. It has been less wonderful for the climate. For thousands of years, plowing has mixed underground carbon-containing compounds with atmospheric oxygen, creating carbon dioxide, the main greenhouse gas that is driving global warming. Researchers estimate that farming throughout history has unearthed roughly 133 billion tons of carbon, an amount equal to almost 14 years of global emissions at current levels.
To prevent climate change from irrevocably damaging human civilization and the world’s ecosystems, humans must reduce carbon emissions enough to prevent the average global temperature from rising more than 1.5 degrees Celsius above preindustrial levels, scientists say. Some areas of the planet have already passed that threshold.
As scientists came to appreciate the threat posed by climate change over the past few decades, some wondered whether carbon already in the atmosphere could be captured and returned to the soil. A team led by Bossio estimated in early 2020 that if soil was protected and replenished globally, it could provide nearly 10 percent of the carbon dioxide drawdown needed to avert near-term climate catastrophe.
Soil carbon building practices, loosely gathered under the term “regenerative agriculture,” have been practiced for decades, or centuries in some places. Planting without tilling the soil took off after the devastating Dust Bowl in the 1930s spurred a search for ways to avert further soil loss, and the practice now includes more than a fifth of U.S. farmland. Maryland has paid farmers to plant cover crops since the 1990s to stanch the flow of nitrogen into the Chesapeake Bay. Some livestock producers rotate animals on pastures of grasses and legumes, whose roots pull carbon underground. And though rare in the United States today, farmers elsewhere in the world mix trees into fields and pastures.
Hill, who farms 10,000 acres, admitted he got into cover crops purely because the state paid him. “We had no intent of doing it for climate,” he said.
But he has since become a true believer. He now mixes rye and other fast-growing grasses with legumes such as clover and lentils, whose roots host nitrogen-fixing bacteria. He also plants root crops such as radishes and turnips to loosen and aerate the soil. While most farmers kill their cover crops in March, as soon as the state allows, Hill lets the plants grow taller than he is, to maximize root mass and carbon gains. He kills them just before planting his cash crop in May.
“The longer the cover crop is alive, the better off we all are,” he said.
There are barriers that keep more farmers from following his lead, Hill said. He has had to buy specialized equipment, and climate-friendly farming hasn’t yet translated to higher yields or premium prices.
“It’s a b---- to farm this way,” he said. Turnips can get stuck in his planting equipment, costing his team valuable time, for example. “It makes life a lot more difficult, and not necessarily more profitable.”
Hill sells most of his corn to the chicken producer Mountaire Farms, which pays him the same market price other suppliers get. If farmers were paid for the carbon accumulating in their soils, they would have greater incentive to adopt climate-friendly practices, Hill said.
But implementing that idea is challenging. Carbon accumulates slowly in soil, and past attempts to pay farmers for it have failed when the costs of verifying carbon gains exceeded what buyers were willing to pay. Backers of new, private-sector carbon markets hope that computer models fed by data from farm fields, satellites and handheld carbon sensors can measure and predict soil carbon gains more cheaply and reliably.
Hill connected with one of those markets, a Seattle-based tech start-up called Nori. After lengthy negotiations, credits representing carbon stored in some of Hill’s fields went on sale in October 2019 at $16.50 a ton — around the most an acre of his farmland might capture in a year, Hill said. Buyers included the e-commerce company Shopify, Arizona State University and individuals looking to offset the carbon their activities produce.
Nori eschews traditional soil tests, which can cost thousands of dollars for a large farm, and instead relies on third-party audits and a U.S. Agriculture Department computer model called COMET-Farm that estimates greenhouse gas emissions from farms.
Nori has competitors. One is Indigo Ag, a Boston-based ag-tech company that has lined up corporate customers including JPMorgan Chase, Boston Consulting Group and Dogfish Head to buy credits for carbon stored in more than a million acres of farmland across 21 states. After farmers upload their 2020 data, Indigo will calculate the amount of carbon stored and verify the numbers with a third party, a process that could take six months.
Still, the emerging market has hit speed bumps. Nori hoped to enroll more than 100 farmers in 2020, but so far, only Hill and an Iowa farmer have sold credits on the marketplace, with three more in the final stage of verification, according to Radhika Moolgavkar, a Nori program manager. At least one potential buyer, Microsoft, which has pledged to go “carbon negative” by 2030, turned down Nori’s credits because they weren’t backed by physical soil samples, Moolgavkar said. A Microsoft spokesperson declined to confirm that account.
“We’re seeing market formation in real time,” said David LeZaks, a senior fellow at the Croatan Institute, a nonprofit organization that researches sustainable investment.
The maturation of soil carbon science has complicated matters. Reduced tillage, already practiced by thousands of farmers, was once considered a major climate win because researchers saw carbon accumulate near the surface of untilled soils. But studies that sampled deeper soil layers revealed that carbon was lost there, wiping out most of the apparent gains.
Cover crops, whose roots and stalks add organic matter to the soil, have become the hotter item. A recent global meta-analysis estimated that if cover crops were planted on 15 percent of the world’s cropland, soils could soak up between 1 and 2 percent of all fossil fuel emissions. In December, Biden announced he wants to pay farmers to plant cover crops, and his USDA transition team has called for setting up a “carbon bank” within the first 100 days of his administration that would pay farmers, ranchers and forest owners for climate-friendly practices.
The USDA already offers three-year grants to encourage farmers to grow cover crops, but those have had limited impact. A 2017 USDA census found that cover crops were grown on less than 4 percent of American cropland.
Some researchers have questioned the practice’s climate benefits. In papers published last year based on long-term research plots in Iowa and California, scientists reported that when they measured carbon in soil to a depth of a meter or more, the gains of cover crops largely disappeared, similar to what had happened to no-till. By contrast, organic farming may do more to build deep reserves of carbon, those and other studies suggest.
Last year, the World Resources Institute, a leading Washington environmental nonprofit organization, stirred debate when it published two blog posts strongly questioning whether farming practices could make a meaningful dent in climate change.
Tim Searchinger, a researcher at Princeton University and senior fellow at WRI who was the lead author of both posts, says cover cropping and other regenerative practices are good for soil and the environment generally, but their carbon drawdown rates are too low to play a major role in averting climate disaster.
“An overfocus on soil carbon is a diversion from the climate strategies that can have a bigger impact,” Searchinger said in an interview. These include restoring carbon-absorbing peatlands, reducing methane emissions from cattle and other ruminants, and increasing the productivity of existing farmland to discourage deforestation.
Soil-based strategies are also limited in duration. Sequestration rates are highest in severely degraded soils, and after a few decades of climate-friendly farming, most soils become saturated with carbon — a fact not always noted by regenerative agriculture promoters, said David Powlson, a researcher at Rothamsted Research in Britain, which hosts the world’s longest-running agriculture experiment: “It’s not like getting rid of a coal-fired power station and replacing it with renewables, where exactly the same carbon savings is happening every year.”
Some fear emerging carbon markets risk wasting a rare opportunity for broader agricultural changes while giving corporations cover from more stringent climate regulations. Large industrial farmers such as Hill already benefit from a bevy of government programs, critics point out, while small-scale farmers with limited acreage will struggle to tap into markets. Expanding existing programs that pay farmers to grow native vegetation rather than crops could be a more cost-effective way to achieve climate benefits, others say.
Still, regenerative agriculture practices appeal to many experts because they’re field-tested and ready to be implemented.
“They are relatively inexpensive, relatively easy to adopt, and have a huge area of land where they’re suitable, and they have tremendous momentum and provide huge benefits to farms,” said Eric Toensmeier, a consultant with Project Drawdown and author of a recent report comparing the climate benefits of dozens of farming practices. “Cover cropping is one of the lowest hanging fruits.”
For Hill, the money from Nori was nice, but he doubts it will be enough to get more traditional farmers off the sidelines. An acre of single-species cover crops could cost $25 to $40 to plant; a biodiverse mix like Hill’s can run $65 an acre. And unlike Hill, most farmers can’t get payments from their state.
Still, between emerging carbon markets, a potential federal program and consumers waking up to the climate costs of food production, Hill is confident that he’s making a move that will be good for both the planet and his bottom line.
“Soil health,” he said, “should be the solution to climate change.”