FOREST GROVE, Ore. — New USDA research is digging into the carbon storage capacity of grass seed crops grown in the Willamette Valley that could benefit farms by providing healthier soils and potential revenue from emissions trading programs such as cap and trade.
Kristin Trippe, a microbiologist at the Agricultural Research Service in Corvallis, shared the results of a study examining carbon stocks in 24 fields growing tall fescue.
While carbon measurements between fields did vary, the average total was 76 tons per acre going to a depth of 40 inches, Trippe told grass seed producers at Oregon State University’s winter seed and cereal crop production meeting Jan. 6 in Forest Grove.
That was higher compared to soil samples collected from fields growing annually tilled crops.
Whether grass straw was baled or left in the field made little difference in the overall amount of soil carbon, Trippe said.
“Even though it’s thousands of pounds per acre, it’s not enough to compete with this incredible pool of deeper soil carbon,” she said.
Interest in gauging soil carbon has been on the rise in recent years as a means to combat climate change and trap harmful greenhouse gases.
Oregon Gov. Kate Brown signed an executive order in 2020 requiring state agencies to adopt policies that will cut greenhouse gas emissions at least 80% below 1990 levels by 2050.
In response, the Oregon Global Warming Commission developed a statewide natural and working lands proposal last year that calls for increasing carbon sequestration by 5 million metric tons of carbon dioxide per year by 2030, and 9 million metric tons per year by 2050, in order to meet those climate objectives.
Planting grass is one of the fastest proven ways to increase soil carbon, Trippe said, since it provides continuous soil cover, allows farmers to till their fields less and returns carbon-rich residue to the ground.
“It makes sense that planting grasses increases carbon,” Trippe said.
Oregon ranks No. 1 in the country in production of several grass seed varieties, including orchardgrass, fescue, ryegrass and red and white clover.
For her project analyzing carbon stocks in grass seed systems, Trippe said she received funding from the Oregon Seed Council. Researchers collected 216 soil samples during the spring, ranging in depth from zero to 40 inches.
Trippe said they chose tall fescue because it represents a large percentage of production in the Willamette Valley — roughly 154,000 acres — with root systems reaching 16 inches deep and stands typically kept for 4-7 years.
Earlier studies had produced mixed results whether baling straw made an impact on the amount of soil organic matter in grass seed fields. Organic matter makes up about 3% of soil, and carbon makes up about 58%.
The project’s findings found that carbon stocks were marginally higher in fields where straw was left on the ground, versus baled.
In older, more established fescue fields, the total was 84.5 tons of carbon when straw was left on the ground, and 72.6 tons per acre when baled. In younger fields, the totals were 70.5 tons of carbon per acre when straw was left on the ground, and 69.8 tons per acre when baled.
“I would caution the numbers are incredibly variable,” Trippe said. “It’s very difficult to aggregate the data, and it’s very difficult to know what’s happening.”
Trippe said their work is far from done. In the future, she hopes to receive funding for more long-term studies at several locations, and work with growers to better understand which management practices result in the most carbon stored.
Those numbers are necessary for grass seed growers to participate in carbon markets and inform regulatory policies, Trippe said.
“You’re working toward that (carbon) potential,” she said. “I think we can do a little better.”