An Iowa State University (ISU) study found planting cover crops between growing seasons can significantly reduce soil carbon loss caused by erosion.
Researchers said that is a benefit often overlooked when measuring the carbon sequestration potential of these conservation practices. The study was led by Wenjuan Huang, ISU assistant professor of ecology, evolution and organismal biology.
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Huang’s study shows that planting cover crops reduces soil carbon erosion by an average of 68%—a factor often left out of carbon market calculations.
While it’s well-established that cover crops reduce erosion, Huang’s study is the first to compile data from individual field trials and evaluate how much carbon is retained in the soil as a result. The research, published in Global Change Biology, analyzed more than 150 experiments and found that cover crops reduced annual soil carbon erosion by an average of 68%.
“We think a lot about how cover crops affect soil carbon levels. But we’ve often focused only on carbon inputs and have ignored outputs,” Huang said in an ISU release.
Huang emphasized that preventing carbon loss through erosion is different from storing additional carbon from plant biomass. Prior research has mainly focused on how roots and plant matter increase soil carbon. But that doesn’t always lead to a net gain.
“Adding more organic matter to soil isn’t a straightforward solution for increasing its carbon stock,” she said, partly because microbial activity can accelerate carbon dioxide emissions.
A previous study co-authored by Huang also found that more diverse crop rotations and the use of livestock manure did not significantly affect soil carbon levels.
“We think a lot about how cover crops affect soil carbon levels. But we’ve often focused only on carbon inputs and have ignored outputs,” she said.
Although cover crops tend to increase soil carbon modestly — an average 14% gain in the top six inches, according to this new meta-analysis—there was no link between that gain and how much erosion was reduced. That’s why Huang said carbon market incentives should treat erosion reduction as a separate environmental service.
“It’s two independent processes, so we really should account for them both,” she said.
The team also examined what factors most influenced soil carbon erosion and storage. Slope steepness had the strongest effect on erosion reduction. When this data was applied to a global farmland map using machine learning, the model estimated that cover crops could reduce soil carbon erosion by 25% globally. In the central U.S., including Iowa, the reduction was estimated at 20%.
“That’s a significant effect,” Huang said, “and it would be even more pronounced on hilly farms and on the edges of fields.”
Beyond carbon retention, cover crops offer other well-documented benefits. “It’s a valuable conservation practice here in Iowa,” she said, noting improvements in water quality and soil resilience.
