Biofuels created from corn crop residues — such as stalks, leaves, cobs, etc — can generate higher levels of greenhouse gases than gasoline, according to new research from the University of Nebraska-Lincoln.
The production of these biofuels — including ethanol — also works to reduce soil carbon, further contributing to greenhouse gas emissions via that pathway.
This new work casts yet further doubt on the usefulness of biofuels with regard to reducing greenhouse gas emissions. Of course, biofuels have a number of other advantages over conventional fuels that will likely see them used in some capacities for some time to come — especially by militaries, and/or governmental agencies.
The work also casts doubt on whether or not “corn residue can be used to meet federal mandates to ramp up ethanol production.”
The press release from the University of Nebraska-Lincoln provides more:
Corn stover — the stalks, leaves and cobs in cornfields after harvest — has been considered a ready resource for cellulosic ethanol production. The US 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.
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 12 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 (a joule is a measure of energy and is roughly equivalent to 1 BTU). Total annual production emissions, averaged over five years, would equal about 100 grams of carbon dioxide per megajoule — which is 7% greater than gasoline emissions and 62 grams above the 60% 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.
“If less residue is removed, there is less decrease in soil carbon, but it results in a smaller biofuel energy yield,” Liska explained.
According to the research, the way to limit increased carbon dioxide emissions and to reduce soil carbon, would be to increase the planting of cover crops — in order to fix more carbon in the soil.
According to Liska, the researchers tried their best to poke holes in the study — but without success. The work appears to be quite solid.
“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,” he continued. “Many others have come close recently to accurately quantifying this emission.”
Of course, the findings aren’t all that surprising to many people — most especially farmers, who have long noted the need to retain crop residue on their fields to protect against soil erosion and to preserve soil quality.
Some more specifics on the work:
Until now, scientists have not been able to fully quantify how much soil carbon is lost to carbon dioxide emissions after removing crop residue. They’ve been hampered by limited carbon dioxide measurements in cornfields, by the fact that annual carbon losses are comparatively small and difficult to measure, and the lack of a proven model to estimate carbon dioxide emissions that could be coupled with a geospatial analysis.
Liska’s study, which was funded through a three-year, $500,000 grant from the US Department of Energy, used carbon dioxide measurements taken from 2001 to 2010 to validate a soil carbon model that was built using data from 36 field studies across North America, Europe, Africa and Asia.
Using USDA soil maps and crop yields, they extrapolated potential carbon dioxide emissions across 580 million 30-meter by 30-meter “geospatial cells” in Corn Belt states. It showed that the states of Minnesota, Iowa and Wisconsin had the highest net loss of carbon from residue removal because they have cooler temperatures and more carbon in the soil.
The new findings were just published in the journal Nature Climate Change.