Study: Cover crops boost water quality, fail to increase carbon storage

Nov. 11 (UPI) -- Cover crops are often planted to restore soil health. New research suggests cover crops can fuel underground microbial communities and improve local water quality, but the vegetation fails to boost carbon storage.

For the study, the results of which were recently published in the journal GCB Bioenergy, scientists collected dozens of soil samples from fields that had undergone long-term cover crop treatments.

When scientists analyzed the samples in the lab, they found the common cover crop winter rye was a boon to microbial activity. Because microbes consume nutrients, their presence and activity helps keep nutrients in the soil, instead of washed away by runoff -- thus, improving the soil health and the quality of nearby waterways.

However, the soil analysis showed the presence of cover crops like winter rye failed to boost carbon storage. Cover crops absorb CO2 and provide an influx of carbon into the soil, but the latest research suggests the majority of that carbon is consumed by enhanced microbial communities and released back into the atmosphere as CO2.

"Cover crops and perennials provide key benefits for water quality, but I wouldn't hang my hat on rapid carbon sequestration benefits," Steven Hall, an assistant professor of ecology at Iowa State University, said in a news release. "We've found a tradeoff. Greater plant growth doesn't necessarily mean gains in carbon sequestration if microbial activity also increases."

Scientists collected the soil samples used for the study from a test field managed by Iowa State researchers. While some fields were planted with a corn-soybean rotation, others were planted with cover crops following continuous corn planting. Some fields featured reconstructed prairies.

Planted prairie natives also failed to boost carbon storage.

"Despite their notable environmental benefits, neither unfertilized perennials nor cover crops necessarily promote rapid soil carbon sequestration relative to conventional annual bioenergy systems because of concomitant increases in decomposition," scientists wrote in their paper.

None of the findings suggest planting cover crops or restoring prairies aren't worthwhile. They offer a range of environmental and ecological benefits -- carbon storage just isn't one of them.