Amid a growing chorus of critics, representatives of two federal agencies have severely questioned the results of a study that purports to tally the greenhouse gas emissions of using corn stover for ethanol production.

In response to the study, the U.S. Environmental Protection Agency released this statement: "This paper 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. As such, it does not provide useful information relevant to the lifecycle GHG (greenhouse gas) emissions from corn stover ethanol. EPA's lifecycle analysis assumes up to 50 percent corn stover harvest. EPA selected this assumption based on data in the literature and in consultation with agronomy experts at USDA to reflect current agricultural practices."

At the same time, Agriculture Secretary Tom Vilsack joined the chorus for a similar refrain. The study makes "certain assumptions about farming operations that aren't a reality," he told the Des Moines Register. "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."

These comments hit home with growers, who know that the corn stover collection cited in the study never comes near the 100 percent level assumed by researchers.

Researchers, led by Adam Liska, PhD, from the biological systems engineering department at the University of Nebraska, contend that removal of corn residue for biofuels can decrease soil organic carbon and increase CO2 emissions because carbon in biofuels is oxidized to CO2 at a faster rate than when added to soil. The team used a supercomputer model at UNL's Holland Computing Center to estimate the effect of residue removal on 128 million acres across 12 Corn Belt states. The researchers’ theory of GHG release was published in Nature-Climate Change journal.

"Research such as this needs to reflect the real world of what farmers do on their fields, not researchers in their ivory towers," said National Corn Growers Association President Martin Barbre. "We're not sure why the federal government felt this study was worth a half-million dollars, when it could much more easily have turned to the in-house experts at EPA and USDA for advice and guidance."

Others in the biofuels industry also spoke out against the study.

"Last week there was a study suggesting the carbon impact of fracking may be 1,000 times greater than previously thought," said Bob Dinneen, president and CEO of the Renewable Fuels Association. "Curiously, that report was largely ignored by the media. Folks need to stop manufacturing scenarios to make biofuels look bad, and begin focusing on the true carbon menace - oil."

And the 25x'25 Alliance released this statement: "It is unfortunate that a study flawed by its assertion of conditions that have no basis in reality could be used to hinder the accelerated development of a biofuel that could decrease emissions by more than 90 percent. We urge policy makers to look at the more credible and nuanced research that exists today and continue their support of a source of energy that will not only boost the economy and enhance our energy security, but improve our environment."