Corn stover for ethanol comes with consequences

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Removing corn stover for use in ethanol production decreases the amount of carbon stored in the soil, and has an adverse impact on overall soil fertility and crop development, according to Ohio State University research.

Humberto Blanco, a research scientist with the School of Environment and Natural Resources within the College of Food, Agricultural, and Environmental Sciences, analyzed the implications of corn stover removal on crop production and soil and environmental quality in long-term no-till fields. He found that as more residue is removed, the greater the loss of soil carbon and crop yields and the more biological processes are compromised.

“There is a linear relationship between corn stover removal and carbon found in the soil. As more residue is removed, the less soil carbon is available,” said Blanco, who is also part of the Carbon Management and Sequestration Center at the Ohio Agricultural Research and Development Center. His study, “Soil and crop response to harvesting corn residues for biofuel production,” has just been published in the October 2007 edition of Geoderma: A Global Journal of Soil Science.

As ethanol demand increases, turning to corn as a source of energy is becoming more common. But little is known about the impacts of residue removal on carbon sequestration, crop production, soil fertility and water quality.

“The purpose of the study is to determine the maximum amount of corn stover that we can remove before the process adversely impacts crop yields, and soil and environmental quality,” said Blanco. “The threshold levels of stover removal as biofuel feedstocks have not been well defined in the Corn Belt.”

Over three years, Blanco removed corn stover at different rates (0, 25, 50, 75, and 100 percent) at three OARDC sites in Ohio: the North Appalachian Experimental Watersheds in Coschocton, the Northwestern Agricultural Experiment Station in Hoytville, and the Western Agricultural Experiment Station in South Charleston. He suggests that the impact of corn stover removal is dependent upon soil and terrain characteristics, such as clay content, drainage and slope gradient.

“Corn stover removal had more of an adverse impact in silt-loam soils on undulating terrains than in clay soils on flat terrain,” said Blanco. “Sloping and erosion-prone soils are impacted the greatest, which suggest that those types of land should not be targeted for residue-removal, or just a fraction of stover might be available for removal.”

Removal rates of more than 25 percent from sloping soils significantly reduced soil carbon concentrations, while as much as 75 percent of corn stover might be removed from clay soils over three to five years before having a negative impact on soil carbon content. Thus, in sloping lands and erodible soils, only about 25 percent of corn stover could be removed without affecting soil or environmental quality.

Blanco also found that large-scale removal of corn stover has an adverse impact on earthworm populations and crop yields. Earthworms are important to soil fertility and water and air movement in the soil.

“Removing corn residue impacts the presence of earthworms. In cases where the residue was completely removed there were no earthworms to be found. Without earthworms, soil porosity, organic matter content, soil structure and water infiltration were all impacted. These are all necessary for a good soil,” said Blanco.

On sloping soils, crop yields suffered as more corn residue was removed from the soil.

“At the start of the season, the percentage of plants germinating was higher from plots without stover, but as the season progressed, things changed. Plants amid residue may have emerged more slowly, but were developing faster as the season progressed and yielded better at the end,” said Blanco.

Removing up to 50 percent of corn residue decreased yields in sloping lands by an average of 1,740 pounds per acre or about 31 bushels per acre.

Blanco suggests that the presence of residue helps to regulate soil temperature and store more water for plant use, resulting in higher crop yields.

“The results of the study suggest that rather than relying solely on corn stover as a source for ethanol production, it’s important to seek other energy alternatives,” said Blanco. “Continuous, large-scale residue removal could have a negative long-term impact on carbon and soils.”

Blanco’s research is anticipated to continue for the next decade to determine the long-term impacts of stover removal and establish the maximum levels of removal.

The study was funded by the Department of Energy.

Ohio State University press release



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