Deep-rooted grass stores significantly more carbon, says new study

Soil biologist Eric Slessarev has some advice for conservationists, landscapers, and farmers with fallow fields: Go touch deep-rooted grass. Or better yet, go plant some. Slessarev, an assistant professor of ecology and evolutionary biology in Yale’s Faculty of Arts and Sciences, is the first author of a new study in Earth’s Future showing that deep-rooted grasses store significantly more carbon in their root biomass than shallow-rooted crops—without harming the existing organic material already in the ground.

The study helps confirm longstanding assumptions about the potential climate benefits of planting deep-rooted grass as a meaningful way to store organic carbon, replenish nutrients, and prevent erosion in soil. It also explores the implications of using perennial grasses as an alternative biofuel source that doesn’t deplete soil as much as crops such as corn do.

“If we can find a role for perennial, deep-rooted plants in the larger economy, it will be a benefit to everyone,” said Slessarev, who is a member of the Yale Center for Natural Carbon Capture. “There is so much going on in the soil, in these deeper layers, that is worthwhile to study and understand.”

Slessarev is co-corresponding author of the study with Erin Nuccio, a researcher at Lawrence Livermore National Laboratory in California.

For the study, the researchers analyzed soil at a dozen sites in nine U.S. states, comparing samples from beneath deep-rooted switchgrass—a common prairie grass with a root depth of 5 to 10 feet—with samples beneath shallow-rooted crops. The study included sites in Oklahoma, Texas, Mississippi, North Carolina, New York, Michigan, Illinois, Wisconsin, and South Dakota.

The switchgrass stored an additional 0.58 metric tons of carbon per hectare in its roots compared to shallow-rooted annual crops, the researchers found.

“Overall, this helps corroborate the idea that switchgrass and other deep-rooted plants can be beneficial to soil health,” Slessarev said. “It’s a night and day difference.”

The work of conducting the study was painstaking, he noted. The team took more than 700 soil core samples and carefully isolated the roots in each sample by hand. They used radiocarbon isotopes to determine how the roots were chemically influencing the existing soil.

Slessarev went to most of the sites himself, driving a pickup truck that pulled a trailer with soil sampling gear.

“It was a great way to see the country,” he said. “It became a grand adventure for me, full of colors and textures in the soil.”