Although previous studies have indicated significant carbon losses from plowing, a new Agricultural Research Service study indicates that there may not be a huge loss if a farmer plows only once.

U.S. Department of Agriculture soil scientist Lloyd Owens found that it may take 3 to 5 consecutive years of plowing before significant carbon losses develop. But he says that even a year of tillage will greatly damage the soil structure, which increases erosion and impairs water infiltration and soil health.

In addition, the researcher at the North Appalachian Experimental Watershed Research Unit in Coshocton, Ohio, says plowing mixes carbon throughout the plow layer. It also removes carbon from the surface, where it is important for holding plant nutrients and water.

Soil carbon losses are a growing concern because the buildup of carbon dioxide in the atmosphere traps heat on the Earth, contributing to global warming. No-tilling dramatically reduces carbon loss.

Plowing Vs. Carbon

Owens has plowed a half-acre plot near the ridge of a hill each spring for 20 years and another plot for 6 years. Each time, he has measured the carbon in soil samples before plowing.

“For the first few years, you couldn’t notice any loss in soil carbon,” he says. “The upper foot of newly plowed soil held about 19 tons of carbon per acre — the same amount as in the soil sampled from no-till fields and meadows. But eventually, there was a significant loss of carbon in plowed fields, when the level dropped to…