USDA: Leave Some Biomass In Fields

If conservation of soil organic matter is taken into account, the United States at best has to cut in half the amount of cornstalks that can be harvested to produce ethanol, according to an Agricultural Research Service (ARS) study.

Jane Johnson, a soil scientist with the ARS North Central Soil Conservation Research Laboratory in Morris, Minn., found that twice as many cornstalks have to be left in the field to maintain soil organic matter levels, compared to the amount of stalks needed only to prevent erosion.

This doesn't mean harvesting cornstalks for cellulosic ethanol isn't feasible—just that when you add soil organic matter concerns to erosion concerns, it slashes the amount of cornstalks available for conversion to ethanol. For example, 213-bushel-per-acre corn yields leave farmers an average four tons per acre of cornstalks after harvest. Farmers could then harvest about two tons of cornstalks per acre for conversion to ethanol—but only from land with low erosion risks, using little or no tillage.

If the same farmers rotate with soybeans as recommended, they can only remove half again as much biomass for ethanol production, or just one ton per acre, to compensate for the lower biomass left by soybeans.

http://www.ars.usda.gov/is/pr/2007/070425.htm