EnergyClimate benefit of biofuels from corn residue questioned

Using corn crop residue to make ethanol and other biofuels reduces soil carbon and generates more greenhouse gases than gasoline, according to a University of Nebraska-Lincoln study published in the journal Nature Climate Change.

The findings by a UNL team of researchers cast doubt on whether corn residue can be used to meet federal mandates to ramp up ethanol production and reduce greenhouse gas emissions.

Corn stover — the stalks, leaves, and cobs in cornfields after harvest — has been considered a ready resource for cellulosic ethanol production. The U.S. Department of Energy has provided more than $1 billion in federal funds to support research to develop cellulosic biofuels, including ethanol made from corn stover. While the cellulosic biofuel production process has yet to be extensively commercialized, several private companies are developing specialized biorefineries capable of converting tough corn fibers into fuel.

A UNL release reports that the researchers, led by assistant professor Adam Liska, used a supercomputer model at UNL’s Holland Computing Center to estimate the effect of residue removal on 128 million acres across twelve Corn Belt states. The team found that removing crop residue from cornfields generates an additional 50 to 70 grams of carbon dioxide per megajoule of biofuel energy produced. Total annual production emissions, averaged over five years, would equal about 100 grams of carbon dioxide per megajoule — which is 7 percent greater than gasoline emissions and 62 grams above the 60 percent reduction in greenhouse gas emissions as required by the 2007 Energy Independence and Security Act.

Importantly, they found the rate of carbon emissions is constant whether a small amount of stover is removed or nearly all of it is stripped, the study found.

“If less residue is removed, there is less decrease in soil carbon, but it results in a smaller biofuel energy yield,” Liska said.

To mitigate increased carbon dioxide emissions and reduced soil carbon, the study suggests planting cover crops to fix more carbon in the soil. Cellulosic ethanol producers also could turn to alternative feedstocks, such as perennial grasses or wood residue, or export electricity from biofuel production facilities to offset emissions from coal-fueled power plants. Another possible alternative is to develop more fuel-efficient automobiles and significantly reduce the nation’s demand for fuel, as required by the 2012 CAFE standards.

Liska said his team tried, without success, to poke holes in the study.