Emissions from corn stover greater than those from gasoline — DOE-backed study

Source: Amanda Peterka, E&E reporter • Posted: Tuesday, April 22, 2014

The study published yesterday in the journal Nature Climate Change estimated the effects of removing corn crop residues from 128 million acres across 12 Corn Belt states. It found that total annual emissions from producing biofuel out of those residues would be 7 percent higher than those of gasoline averaged out over five years and above the regulatory threshold set by the federal renewable fuel standard for cellulosic biofuel.The study is backed by a $500,000 DOE grant and is likely to factor into the debates in Washington, D.C., over the future of biofuels policy.

The research is already taking heat from the renewable fuels industry, which this year is set to open the first U.S. facilities built to generate cellulosic biofuel from corn stover. The industry says that the research was based on unrealistic assumptions about how much agricultural waste is to be harvested and does not reflect what’s actually happening on farm fields.

“The article says little about real world stover-to-ethanol fuel because it uses corn stover removal rates far exceeding those used in the field,” said Brooke Coleman, executive director of the Advanced Ethanol Council, which represents the companies making cellulosic ethanol. “The analysis also models a one-size-fits-all approach to managing soil carbon that, by definition, ignores how farmers manage their land.”

The model developed by University of Nebraska, Lincoln, assistant professor of agronomy and horticulture Adam Liska found that harvesting corn stover that is currently left on fields decreases soil organic carbon partly by increasing soil erosion by wind and water. Based on a harvest rate of about 2.7 tons of stover per acre per year, Liska found that the emissions add an average of 50 to 70 grams of carbon dioxide per megajoule of biofuel.

Unless the lost carbon is mitigated by certain management practices, such as planting no-till cover crops, corn-stover biofuels will likely not meet 60 percent reduction threshold used by U.S. EPA to define cellulosic biofuels, the study found.

The states of Minnesota, Iowa and Wisconsin showed the highest net loss of carbon because they have cooler temperatures and have more carbon in the soil. The emissions are not properly characterized in EPA’s life-cycle emissions, the study says.

It also found that the rate of carbon emissions is constant no matter how much stover is taken off the field.

“If this research is accurate, and nearly all evidence suggests so, then it should be known sooner rather than later, as it will be shown by others to be true regardless,” Liska said in a statement. “Many others have come close recently to accurately quantifying this emission.”

The major companies set to open cellulosic ethanol facilities this year, though, say they are planning to harvest far less corn crop residue from farm fields than the rate used by the study.

POET-DSM Advanced Biofuels, a joint venture between the nation’s largest ethanol producer and a Dutch enzyme maker, is planning to collect only about a ton per acre, or less than a quarter, of the residue left on cornfields each year after the fall harvest, according to Steve Hartig, the company’s general manager for licensing. POET-DSM plans to open a 20-million-gallon-a-year cellulosic biofuel plant in northwest Iowa later this year and to collect stover from about 120,000 acres within a 30-mile radius.

Previous research, including analyses from Iowa State University, the University of Illinois and Argonne National Laboratory, has found that stover collection rates in the range of 20 to 30 percent — or leaving about 3 tons of stover on the field — likely will not have negative sustainability impacts.

“I think the study is a theoretical thing,” Hartig said in an interview this morning. “You could also take all the stover off the field, you could take none of the stover off the field, and those are all maybe an interesting thing to study from an agricultural point of view, but they have no basis to what we’re doing. And we’re taking about 20 percent, and we’re also consistently working with the farmers on that.”

DuPont’s biofuels branch, which is also planning to open a 20-million-gallon-a-year plant in Iowa, aims to take 160,000 to 170,000 acres of corn stover — or 600,000 stacked bales — to operate its plant. Its harvest rate for stover is also about a ton per acre per year (Greenwire, Dec. 13, 2013).