Why should farmers care about carbon?

Deb O'Dell jumped at the chance when she was invited, along with other scientists, to present a briefing to the Congressional Soils Caucus. Briefing organizers wanted information relating to carbon markets and carbon sequestration.

The topic fit O’Dell like a glove. In her presentation she told Soil Caucus participants about the importance of incentivizing farmers for two key practices: No-till and cover crops.

She pointed out that when working together, the twin practices effectively draw carbon dioxide out of the air.

As an adjunct professor at the University of Tennessee, O’Dell is part of a team of soil and atmospheric scientists who examine the potential of agriculture to sequester carbon and mitigate climate change. She and her team also look for ways to reward farmers for practices proven to build soil organic matter and sequester carbon in the process.

“The need for society to address climate change is critical,” she says. “As levels of atmospheric carbon dioxide continue to rise, warming the Earth, there’s the potential for the entire world to suffer. Here’s an opportunity for farmers to get involved and be a part of the solution.”

Why farmers should care

Farmers and ranchers themselves stand to suffer significant consequences from a warming climate. One increasingly evident outcome of a changing climate is the greater potential for extreme, erratic weather events to impact the conditions under which farmers and ranchers grow crops and raise livestock.

“Record-high temperatures could affect crop production and yields,” says O’Dell. “Working conditions for humans could become more difficult in hot temperatures. In addition, droughts and floods could become more frequent.”

Farmers’ and ranchers’ ability to grow plants and conserve soil has potential to mitigate climate change by drawing carbon dioxide out of the atmosphere and storing it as carbon in the soil. The increased carbon offers the added benefits of improving soil quality and sustaining crop yields.

“Plants harvest sun energy and atmospheric carbon dioxide,” she says. “They use this to produce organic carbon building blocks to grow leaves, stems, and roots.”

When left undisturbed by tillage, above-ground plant material helps build organic matter on the soil surface. As soil biological activity fosters root decomposition below ground and surface plant residue degrades on the surface, carbon in the soil increases, and is stored — or sequestered — as organic matter in the soil.

Grass and cover crops

The most effective ways farmers and ranchers can manage plants and soils to best help mitigate the harmful effects of climate change is to avoid grassland conversion and to grow cover crops. This is the premise of a study published in 2018 in Science Advances. The multi-agency study showed that out of 11 agricultural and grassland management practices, avoiding grassland conversion into cropland and growing cover crops are the natural climate solutions holding the greatest potential to draw down atmospheric greenhouse gases by the year 2025.

However, cover crops can fulfill their role as soil carbon builders only when teamed with no-till.

“Organic carbon stored in plant residues and soil can be decomposed and emitted back to the atmosphere as carbon dioxide,” says O’Dell. “Tillage must be minimized in order to protect the soil from increased decomposition of organic carbon and degradation from soil erosion.”

In a somewhat different but related vein, no-till by itself is less effective at building soil carbon than is no-till practiced in partnership with growing cover crops. A University of Kentucky study separate from O’Dell’s work indicates that no-till paired with cover crops increases carbon in the soil, while no-till without cover crops is less effective at enhancing soil carbon.

The results of a meta-analysis of global soil carbon changes due to cover cropping published in Soil Biology and Chemistry “showed that including cover crops into rotations significantly increased soil organic carbon, with an overall mean change of 15.5%,” according to the study’s abstract.

“This is one reason agriculture has great potential to increase carbon sequestration,” says O’Dell.

Room to grow

However, this potential can only be realized as more farmers grow cover crops. While cover crops’ benefits to soil and crop resilience have indeed caused more growers to plant more acres to cover crops, the overall adoption rate leaves plenty of room for that acreage to grow.

According to O’Dell’s research drawing from a 2018 study using 2017 USDA census data of cover crop land use practice by farm acreage for each county, just 12% or less of surveyed fields used cover crops or double cropping.

She cites similar data indicating increasing acceptance of no-till across the country, yet with plenty of room for expansion. The 2018 study based on 2017 census data indicated the current U.S. adoption rate of no-till is about 21% for the top four U.S. crops.

Paying producers to grow cover crops or double crop as well as practice no-till is key to increasing the U.S. acreage producing “something green all the time” with no tillage, says O’Dell. Thus, the combined practices that sequester carbon make them an obvious fit for farmers looking to participate in the emerging carbon marketplace.

However, O’Dell cautions growers that before entering agreements, farmers should understand whether or not certain markets require verification — through some form of measurement — of the amount of carbon actually sequestered. Soils’ expected response to conserving practices can vary in both carbon-sequestration amounts and length of time to sequester carbon.

“In some cases, it can take as long as five to 10 years after adopting regenerative practices for measurable changes to occur in soil carbon,” she says.

Payment for services rendered

While carbon markets offer one form of incentive for farmers to adopt regenerative methods such as no-till and growing cover crops, O’Dell suggests that farmers should be paid — as a matter of course — for implementing both, along with a range of other regenerative practices.

“They should be paid for providing environmental services,” she says. While some of these services benefit farmers directly, all improve environmental conditions and stabilize food security.

“The bottom line is that, in addition to sequestering carbon to mitigate climate change, cover crops combined with no-till conserve resources including water, soil, and soil organic matter,” she says. “They reduce dependence on chemical inputs and reduce use of fossil fuels required by the tillage process. They improve soil quality, and maintain and improve yields over time.

“Cover crops and no-till reduce soil erosion and degradation,” she continues. “They also reduce surface runoff, improving water quality and reducing loss of nutrients. They lead to improved soil structure, thus increasing water infiltration, which reduces flooding impacts and enhances crop resilience to drought. They also increase soil organic matter, which improves soil quality and crop yield, while reducing dependence on inputs of chemical fertilizers.

“Farmers should be rewarded for providing these environmental services to society,” she adds, “whether they’ve been implementing regenerative practices for a short time or for a long time.”