The national push for biofuels may encourage farmers to plant corn where environmentally friendly grasses are now grown. But those making the switch can still sequester soil carbon and reduce greenhouse gas emissions by not tilling the soil, according to Agricultural Research Service (ARS) scientists.

Ron Follett, a senior supervisory scientist at the ARS Soil Plant Nutrient Research Unit in Fort Collins, Colo., spent six years monitoring levels of soil organic carbon in a Nebraska field where brome grass was grown for 13 years and the field then was converted to no-till corn.

The effort is one of the most comprehensive field studies yet to address a major issue in agriculture: the effects of replacing native grasses with corn. Bromegrass became a popular alternative in the 1990s for Midwestern farmers trying to save erodible soils, enhance habitats and increase soil organic carbon. Under conventional tillage, much of this carbon is released into the atmosphere as carbon dioxide, a greenhouse gas that contributes to global warming. Nationwide, there are 35 million acres of bromegrass and other plants grown in exchange for $1.8 billion in annual payments as part of USDA's Conservation Reserve Program.

But as demand for biofuels raises corn prices and CRP contracts end, farmers may replace grasses with corn.

Follett and his team used herbicide to kill the grass in the fall of 1998 and planted no-till corn the following spring. They collected soil samples at three depths to analyze the total amount of soil carbon at each depth and determine whether the carbon was previously sequestered by bromegrass or newly sequestered by the corn.

Follett's results, recently published in Agronomy Journal, show the benefits of no-till when making the switch. The researchers found yields were decreased because of extended drought conditions, but the total amount of carbon didn't change. The rates of loss of soil organic carbon previously sequestered in the top two depths by the bromegrass were offset by similar rates of increase in newly sequestered carbon from the corn. There also was little or no change in the amount of soil organic carbon from either the bromegrass or the corn at the third depth.