WASHINGTON, April 23, 2014 - The biofuels industry is dismissing as “deeply flawed” a University of Nebraska-Lincoln study that claims using corn crop residue to make ethanol and other biofuels reduces soil carbon and can generate more greenhouse gases than gasoline.
Published Sunday in Nature Climate Change, the study from a UNL research team led by assistant professor Adam Liska used a supercomputer model to estimate the effect of residue removal on 128 million acres across 12 Corn Belt states. The team said it found that removing crop residue from cornfields can result in up to 7 percent greater greenhouse gas emissions (GHGs) than gasoline.
The research, funded through a $500,000 Energy Department grant and under way since 2007, used USDA soil maps and crop yields, extrapolating potential carbon dioxide emissions across 580 million 30x30-meter “geospatial cells” in the Corn Belt states.
The Renewable Fuels Association (RFA), however, says the study is not only contradictory to current science, but also “shows a complete lack of understanding of current farming practices.”
RFA CEO and President Bob Dinneen said the study’s methodology “is fundamentally flawed and its conclusions are highly suspect.” He said the results are based on “sweeping generalizations, questionable assumptions, and an opaque methodology.”
Liska asserts that until now, scientists, hampered by limited carbon dioxide measurements in cornfields, have not been able to fully quantify how much soil carbon is lost to carbon dioxide emissions after removing crop residue.
However, industry leaders say recent research, including an analysis conducted by the University of Illinois and DOE’s Argonne National Laboratory, showed removing 30 percent of the residue results in no additional carbon emissions. In fact, the research found that removing even more corn stover – stalks and leaves will maintain soil organic carbon at more than acceptable levels. Early results from a South Dakota State University study show that carbon levels remained constant from 2008-2012 in a system with relatively high residue removal rates.
The UNL study bases its findings on a 75-percent stover removal rate post-harvest, a level biofuel advocates say is far above that recognized through current farming and land management practices as needed to maintain the soil’s ability to retain carbon and produce a feedstock that can significantly reduce emissions, when compared to its gasoline equivalent. Dinneen said the study is a “modeling exercise of a hypothetical scenario that bears no resemblance to the real world.”
Other points of contention raised by the RFA include the assertion that the study makes no distinctions with regard to tillage practices, that it “absurdly” suggests soil carbon loss is perfectly linear with the stover removal rate, and that it incorrectly assumes “no mitigation action is taken” to prevent carbon losses or replace lost carbon.
Jan Koninckx, global business director for biorefineries at DuPont, said the study’s “core analysis depicts an extreme scenario that no responsible farmer or business would ever employ because it would ruin both the land and the long-term supply of feedstock. It makes no agronomic or business sense.”
Brooke Coleman, executive director of the Advanced Ethanol Council (AEC), said the Associated Press (AP) story that disclosed the study “is an article trying to package itself as saying something completely new; that removing corn stover from the field has newly quantified impacts that would change our perception of making advanced ethanol out of corn stover.”
Coleman said that “in reality, the study confirms what we already know; that excessive agricultural residue removal is bad for the soil and has negative impacts on climate.”
The Obama administration also weighed in, with EPA issuing a statement that said the study “is based on a hypothetical assumption that 100 percent of corn stover in a field is harvested; an extremely unlikely scenario that is inconsistent with recommended agricultural practices.” An EPA spokesperson later added that the study “does not provide useful information relevant to the life cycle greenhouse gas emissions from corn stover ethanol.”
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