Dedicating Too Much Corn Stover to Ethanol May Increase Soil Erosion, Says USDA’s Ag Research Service

One feedstock often mentioned in discussions about cellulosic ethanol is corn stover, the stalks, leaves and cobs left over after harvesting is completed. But removing a large amount of corn stover from harvested fields could prove counterproductive to efforts to prevent soil erosion and maintain soil organic matter, according to findings by USDA’s Agricultural Research Service.

In fact, one ARS study concluded that if conservation of soil organic matter is taken into account, the US should plan on cutting in half the amount of cornstalks that can be harvested to produce ethanol.

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, said Johnson, its just that when soil organic matter concerns are combined with 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 remove only half again as much biomass for ethanol production, or just one ton per acre, to compensate for the lower biomass left by soybeans.

GASMAN’s Comments, … by the way, though this study notes a 213 bushel per acre yield, according to the USDA, the average yield is 155 bushels per acre. That is a LOT lower, and thus means much less stover for cellulosic ethanol.