In Producing Ethanol, Some Cornstalks Should be Left in
By Don Comis
April 25, 2007
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)
Johnson, a soil scientist with the ARS
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
feasiblejust 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 ethanolbut 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.
Johnson's estimates are part of the Renewable Energy Assessment Project
(REAP), formally created in 2006, although she and a core group of colleagues
have worked on these measurements for several years prior.
REAP was formed to ensure that cellulosic ethanol programs will be
sustainable. Most participants work with corn, but others work on switchgrass
for cellulosic ethanol. When cellulosic ethanol is made from corn, it uses
cornstalks as well as grain.
There are nine ARS locations participating in REAP in eight states, from
Alabama to Indiana to Oregon.
The new program also aims to compare the economic value of biomass for
bioenergy versus its value for storing soil carbon. REAP will provide
guidelines on harvesting biomass to corn farmers, land managers, the biomass
industry and action agencies.
Johnson also explored the use of a byproduct of ethanol fermentation as an
organic additive to soils. This is an example of the innovations needed to
support residue removal.
ARS is the U.S. Department of
Agriculture's chief in-house scientific research agency.