Donnelle Eller,

deller@dmreg.com;

Experts on Monday criticized a new University of Nebraska-Lincoln study, saying it used “worst-case” assumptions to determine that cellulosic ethanol creates more carbon emissions than gasoline.

The report from Adam Liska, an associate professor at Nebraska, says crop residue used to make cellulosic ethanol creates 7 percent more greenhouse gas emissions in the short-run than gasoline emissions and are “above the 60 percent reduction in greenhouse gas emissions” required by the federal government.

Tom Vilsack, the U.S. secretary of agriculture, said the study makes “certain assumptions about farming operations” that “aren’t a reality. It’s not what’s happening on the ground.

“If you make the wrong assumption, you’re going to come up with the wrong conclusions,” said Iowa’s former governor, who was in Des Moines on Monday. “It’s unfortunate.”

The U.S. Department of Energy provided a $500,000 grant over three years for the study, published Sunday in a peer-reviewed journal, Nature Climate Change. The research attempts to quantify, over 12 Corn Belt states, how much carbon is lost to the atmosphere when the stalks, leaves and cobs that make up residue are removed and used to make biofuel, instead of left to naturally replenish the soil with carbon.

The university said the study “casts doubt on whether corn residue can be used to meet federal mandates to ramp up ethanol production and reduce greenhouse gas emissions.” The federal government has provided more than $1 billion in funding to support what it believes is greener cellulosic ethanol development.

In November, the U.S. Environmental Protection Agency proposed pulling back how much renewable fuels — including corn-based and cellulosic ethanol and biodiesel — must be used in the U.S. fuel supply. EPA has reduced the target for the cellulosic industry five times, given the industry’s difficulty in meeting the volumes.

Jennifer Dunn, an environmental team leader at the Argonne National Laboratory, said the study looked at “extreme levels of corn stover removal — up to 100 percent.”

A study from Dunn and others in 2012 found that biofuels made with corn residue were 95 percent better than gasoline in greenhouse gas emissions. That study assumed some of the corn stover harvested would be used to create energy and replace power produced from coal.

“The general consensus has been that we would manage corn stover removal to avoid adverse impacts to soil health, including a decline in soil organic carbon,” Dunn said.

Dunn said several plants are creating energy to power their own cellulosic plants, a fact not factored into the Nebraska study. That includes Poet-DSM, which is building a $250 million cellulosic plant in Emmetsburg.

Another Iowa plant, DuPont Nevada, says its $225 million facility has the potential to reduce greenhouse emissions by more than 100 percent. It’s under construction west of the Story County town.

“The companies behind these plants have really striven to emphasize the sustainability of their feedstock, including the soil carbon aspect. It’s why there is only a certain level of stover that can be removed from the field.

“Everyone knows that if you take the whole thing off, it’s going to cause problems,” she said. “That’s not even debated. ... Nobody wants to damage their soil health.”

Dunn and others say farmers look at soil carbon on a “sub-field level” to determine how much stover can be sustainably removed.

Liska said in an email that his study looked at stover removal at 25 percent, 50 percent and 75-100 percent, and the rate of carbon emissions was constant. “It is likely that no matter what level of residue is removed, the carbon intensity stays the same,” he said.

Douglas Karlen, a research soil scientist with USDA’s Agriculture Research Service, said the amount of stover removal used in the model isn’t physically possible. “If you could take off 75 percent of the corn stover, I’m not sure where you would put it,” he said.

Karlen said Iowa farmers would take off 1 to 1.5 tons per acre of stover from their fields. The study model would remove 2.68 tons per acre.

“You’d be stacked up with corn bales that are miles long,” said Karlen, who has worked with both Poet and DuPont in Iowa, among other companies, on ensuring sustainable amounts of stover are removed. “The machinery can’t take off 75 percent of the material, even with a vacuum system.”