Amount of planet-warming carbon dioxide that Oregon farmland absorbs overinflated, study finds

Boosting the power of crops and soils on Oregon farms and ranches to absorb and store more greenhouse gas emissions is one of many tools that state and federal leaders are investing in to combat climate change.

But the amount of planet-warming carbon dioxide that can be naturally removed from the atmosphere by being stored in crops and their soils is vastly overinflated, according to new research in the journal Earth’s Future. Researchers found that the actual potential is about one-fifth of estimates often cited by the U.S. Department of Agriculture and the Environmental Protection Agency, and a small fraction of the total carbon dioxide emissions from agriculture annually.

The findings question whether investments in carbon removal, or carbon sequestration, on “natural and working” farmlands would be better spent on other actions to reduce emissions and mitigate climate change. Researchers encouraged natural resource agencies to consider investments in conservation practices on farmland as investments in soil health, rather than stand alone solutions to climate change.

“On its own, increasing carbon sequestration via conservation practices on U.S. croplands will be insufficient to achieve agriculture’s climate mitigation goals,” the researchers wrote, emphasizing, “the importance of allocating scarce mitigation resources as judiciously and cost effectively as possible, and to pathways with less uncertainty about expected mitigation.”

The findings come amid an Oregon push to encourage more agricultural storage of carbon dioxide from the environment, with the Legislature allocating $10 million towards’ such efforts last year. And Congress also has approved billions for conservation practices in agriculture to help with climate change, including storing greenhouse gases.

The study gives a perspective on how valuable those investments might be as a way to reduce the amount of greenhouse gases in the air. Five researchers from universities across the U.S. collaborated on it, including Daniel Bigelow, a natural resource economist at Oregon State University.

Bigelow looked at the durability, or long term predictability, of storing atmospheric carbon on farmland by focusing on the best parts of the U.S. for “cover cropping.” That’s where farmers continue to plant different crops during non-growing seasons to ensure there are always plants in the soil. This keeps soil healthy and fixed in place, including the soil carbon. For this, Bigelow and the researchers had to pick farmland that had annual crops and that would not require extra irrigation for growing cover crops. Adding irrigation during the off season would not be considered durable, or sustainable, in perpetuity, because groundwater in many parts of the U.S. has been overdrawn for decades. It’s likely cover cropping would be only temporary in parts of the U.S. without consistent water supplies, Bigelow said.

In Oregon, this limits the best areas for cover cropping to parts of the Willamette Valley, such as Linn County. Across the U.S. it limits the best cover cropping for carbon sequestration to parts of the corn and soy belt in the Midwest, where cereals and grasses could be planted during the winter offseason without extra water.

“Given the diversity of Oregon’s agricultural sector, especially west of the Cascades, it’s kind of harder to imagine it being a big part of the solution,” Bigelow said.

Nevertheless, millions in state and federal dollars have been allocated to encourage more Oregon farmers to grow crops during non-growing seasons – what’s called “cover cropping” – and to employ other techniques such as refraining from tilling the soil, which disturbs the microorganisms within the soil that suck up carbon dioxide. These methods have been well known to improve soil health for years, but it wasn’t until recent years that they were recognized as a climate change solution.

“There are benefits to the producer from cover cropping. Your yields could be better; you’re reducing soil erosion,” Bigelow said. “But this wasn’t invented as a carbon sequestration technique. It’s about soil health.”

Last summer, Gov. Tina Kotek signed House Bill 3409 to invest $10 million in “natural climate solutions” on “Oregon’s working lands.” This includes farm, ranch and forestlands as well as marine ecosystems. The independent Oregon Climate Action Commission, which monitors and evaluates the government’s action on climate change, has included cover cropping as a potential beneficial investment.

The commission is still in a learning and planning phase, according to Chair Cathy Macdonald. Macdonald is also the North America director of natural climate solutions for the nonprofit The Nature Conservancy. She said commission members are still thinking about the best return on investment for carbon sequestration projects in Oregon, and where that leaves farmland and investments in cover cropping. She said they have to think across sectors and not only for reducing emissions across natural resource industries, but also for helping those industries adapt to climate change.

“There are a lot of benefits from cover crops, and I think a lot of what we’ve invested in, collectively, through the farm bill and other programs in cover crop adoption, have been for a multitude of benefits,” she said. These include improved water quality, weed control and nutrient management on farms, which also aid soil health, which in turn has a net carbon benefit.

“It’s important for us to have all the tools in the toolbox, and it’s important for us to weigh the potential benefits of those different tools, so it is what we think about,” she said when it comes to priorities for state investment.

The Inflation Reduction Act passed by Congress in 2022 provides $19.5 billion over five years to support the U.S. Department of Agriculture’s conservation programs that yield climate benefits, including payments to farmers to help pay for the upfront costs of cover cropping. The Biden administration has committed to restoring and preserving 30% of U.S. land and water by 2030 and 50% by 2050 to better mitigate climate change.

The researchers found that if cover cropping occurred across the U.S. on all suitable farmland – about 30% of all cropland in the U.S. – it could double the carbon dioxide that these lands currently absorb from the atmosphere. But this would reduce annual carbon dioxide emissions from agriculture in the U.S. by just 3%. This is one-third of the 10% reduction in greenhouse gas emissions the USDA has claimed cover cropping could cut. Agriculture is responsible for about 10% of the U.S.’s overall annual greenhouse gas emissions.

“It’s (cover cropping) certainly not a panacea for solving the problem of mitigating agriculture related greenhouse gas emissions,” Bigelow said. “There are gains to be had there, but they’re just small. I don’t want to call it a drop in the bucket, but it’s small. It’s not a game changer.”

Oregon Capital Chronicle is part of States Newsroom, a network of news bureaus supported by grants and a coalition of donors as a 501(c)(3) public charity. Oregon Capital Chronicle maintains editorial independence. Contact Editor Lynne Terry for questions: info@oregoncapitalchronicle.com . Follow Oregon Capital Chronicle on Facebook and X.

Reporting for this story was supported by the MIT Environmental Solutions Journalism Fellowship.