The U.S. Department of Energy has been counting on leftover residue from corn cultivation—such as  stalks and cobs—as an abundant future source of renewable clean energy, and touted it as a potential goldmine for farmers as well.

But University of Nebraska-Lincoln (UNL) researchers may throw a damper on those plans, with a newly published study in the scientific journal Nature Climate Change. They calculated that harvesting the corn residue may actually result in the release more climate-altering carbon dioxide into the atmosphere than federal environmental regulations allow. (See related coverage: “Biofuels at a Crossroads.”)

Those findings, however, were challenged by both a renewable energy trade group and a prominent biofuels researcher, who found fault with the study’s methodology.

The UNL team, led by agronomy and horticulture assistant professor Adam Liska, used a supercomputer simulation to estimate the effect of removing the corn residue (also called corn stover) from 128 million acres across 12 states in the Midwest’s Corn Belt.

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If left undisturbed, most of the residue rots, releasing carbon dioxide into the atmosphere, but some of the material also becomes part of the soil, storing its carbon there.  But when the corn residue is removed, converted to biofuel and burned in engines, it pumps out carbon dioxide more rapidly than a cornfield would release it, the researchers wrote. As a result, they calculated, biofuel made from corn residue would release so much carbon that it would probably exceed the limits set by federal regulations, which require biofuels to produce 60 percent fewer greenhouse gas emissions than gasoline. (Take the quiz: “What You Don’t Know About Biofuel.”)

The study’s lead author, UNL agronomy and horticulture assistant professor  Adam Liska, declined to be interviewed by phone. In an email, he said that additional unpublished data shows that when both the actual corn and the corn residue are removed, “there is a net loss of soil carbon and there is also an absolute loss of soil carbon to the atmosphere.” In contrast, if only the corn itself was harvested for biofuel, on average the carbon going into the atmosphere would be canceled out by the amount going into the soil. (See related story: “Squeezing Gasoline from Plants.”)

The corn residue study, which was funded by a three-year, $500,000 grant from the U.S. Department of Energy, could signal a major problem for the nascent biofuels industry, which is heavily invested in using such waste material as a way to avoid competing for food supply with the use of actual corn.

Paul Winters, an official with the Biotechnology Industry Association, a biofuels trade group, said that corn residue is expected to provide three billion gallons of biofuel by 2022, or about 20 percent of the total production of cellulosic ethanol—that is, fuel produced from the inedible parts of plants.  The study has no implications for materials such as switchgrass, a plant that is cultivated specifically for fuel. “You’re just harvesting the top, not disturbing the soil and the carbon in it,” Winters explained.

But Winters found fault with the UL study, saying that the computer model didn’t take into account the varying soil and other conditions in individual cornfields, or the careful efforts by biofuel producers to work with farmers to monitor how harvesting corn residue affected the carbon content of the soil. “The companies who are doing it now only take about 25 percent [of the corn residue],” he said. “They leave 75 percent on the ground.” (See related story: “U.S. Drought Fuels Debate on Ethanol.”)

John Sheehan, an engineer, biofuels entrepreneur and former researcher for the National Renewable Energy Laboratory who helped lead key research on the use of corn residue, said that he planned to contact Liska and raise questions about his methods. Sheehan said the study’s relatively short 10-year time scenario gave a misleading impression of the proportion of carbon that ended up in the atmosphere. The loss of soil carbon is highest in the first few years when corn residue is harvested, but it tends to decrease over a 20- to 30-year period, he said.

Liska “is using the most extreme response of the system as an indicator,” Sheehan said.

Sheehan also argued that the UNL researchers’ new model for calculating soil carbon loss failed to take into account variations in microbial activity and respiration rates in different corn fields, which are influenced by how farmers till the soil. “The respiration for aggressively tilling, versus conservation tillage, is very different,” he said.  That, in turn, could produce big variations on how much carbon is stored or released. (Share your thoughts: “What Breakthroughs Do Biofuels Need Now?“)

In a second e-mail, Liska defended his team’s use of the shorter time frame. “Everyone really wants to know how these systems will perform in the first 10 years,” he said. He said that biofuels makers could switch to another source of material for fuel, or else plant cover crops in the fields to mitigate  carbon loss.  “The carbon lost in any residue that is removed must be either replaced or off-set somewhere else in the system,” he wrote.



  1. sajeew
    August 22, 2014, 1:49 am

    Plant material harvested from the ground does not only contain CO2 and water but also minerals and nitrogen from the earth.

  2. Henry Gibson
    April 28, 2014, 1:33 am

    Every article on bio-fuels should mention that 15 million children die of hunger every year, but also if all of the crop land in a country the size of the US were used for bio-fuel production it could not produce one tenth of the fuels used in the US.

    Plant material harvested from the ground does not only contain CO2 and water but also minerals and nitrogen from the earth. These minerals and nitrogen and water must be replaced in the highly productive maize fields with minerals and nitrogen harvested elsewhere by mining and manufacturing that uses vast amounts of fossil fuels to make and transport and spread on the fields. You can find on a website somewhere that the US government calculates that there is an energy gain of 20 percent perhaps from using fossil fuels in this way to produce bio-fuels but vast amounts of labour and capital equipment and land are needed to make bio-fuels and process fossil
    fuels that facilitate the production of bio-fuels and sustain the workers required for the bio-fuel production as well as those who produce the fossil fuels for the production of the bio-fuels and those that produce the fertilizers.

    It is easy to calculate that natural growth of plants on those farming areas now used for bio-fuels combined with harvesting such plants or trees and storing the the harvested materials forever in salt caverns would reduce CO2 release far more than forcing the growth of high production plants, as we do now, and converting them to bio-fuels for burning.

    ARTEMIS of the UK demonstrated in a production automobile that was modified with their hydraulic hybrid transmission that the fuel use of city driving could be reduced to half of what is now used without any change to a smaller engine which would reduce the fuel use even more. One third of the fuel is saved in distance driving. This would apply to all vehicles. The new transmission also gives better acceleration and hill climbing ability. The transmission can be made and repaired at far lower costs than electric hybrids and are more efficient for less weight. These transmissions are now being tested in some of the largest production wind turbines because of their high reliability, flexibility and low cost and the ability to use the flywheel energy in the rotating blades down to half speed or less to support grid operation in an emergency without any damage to gears or transistors even at double power for a few seconds.

    Starting the process of cutting the US automobile fuel use in half with this low cost transmission would be better use of any bio-fuel subsidies or grants or money spent at the pumps for ethanol or any other bio-fuel. This can be combined with the use of diesel engines in all US vehicles which are more efficient and the fuel is far less expensive to refine from crude oil and less CO2 is released in the production of the fuel. Catalysts, filters and the Artemis transmission will almost eliminate all of exhaust problems associated with the older diesel vehicles and produce far less CO2 in the process. ..HG..

  3. gak
    April 24, 2014, 4:18 am

    You do realize that biofuels’ function is to serve as a substitute for oil, don’t you?
    The idea is that, you grow corn, which captures some co2 from the atmosphere. You process the corn and make fuel out of it. Burn the fuel and release the co2 captured by the corn, back to the atmosphere. Rinse and repeat the cycle as much as you like. You don’t add co2 to the atmosphere, in the medium-long term. (assuming the tractors, trucks, process etc. does not use conventional oil).
    If you use the ordinary oil (the one Texans or Saudis happily sit on), you take co2 from the depths of the earth’s crust, and introduce it to the atmosphere. In the short, medium, and long term, you add co2 to the atmosphere.


  4. Devin Combs
    April 23, 2014, 7:36 pm

    Unfortunately, it is not looking as though corn and therefore ethanol is proving to be an efficient source of fuel. We are already spending an enormous amount of subsidies for ethanol, even compared to other renewables, and further issues such as the one presented here, just make more of a case that we need to be cautious about continuing to invest highly in ethanol.

  5. a p garcia
    April 22, 2014, 8:50 pm

    From the laws of thermodynamics and conservation of matter, I just knew I was no panacea in energy. Unfortunately lawyers, politicians, and bureaucrats don’t study the laws of science!