Removing corn stover from agricultural fields to produce cellulosic ethanol requires careful management to avoid adding greenhouse gas emissions and soil erosion to the environment, say Purdue University researchers.

Environmental impacts from stover removal can be reduced by switching to no-till corn or adding winter cover crops, but these practices likely would increase production costs, researchers reported in a study.

"Some crop rotation and tillage combinations are more environmentally benign than others," said Ben Gramig, a Purdue agricultural economist and the study's lead researcher. "But there are water quality and greenhouse gas tradeoffs when collecting stover."

Stover is the parts of a corn plant that remain after grain harvest. Greenhouse gases from cropfields are released into the atmosphere when carbon escapes disturbed soils during stover removal. Emissions also occur when nitrogen fertilizer is applied to the land or crop residues decompose. Plowing fields loosens soil and, when combined with removing stover, causes increased soil erosion.

Federal law requires 16 billion gallons of cellulosic ethanol be produced each year as part of the U.S. Renewable Fuel Standard. One RFS goal is to reduce the amount of greenhouse gas emissions. Greenhouse gases are believed to contribute to climate change.

The Purdue study, "Environmental and Economic Trade-Offs in a Watershed When Using Corn Stover for Bioenergy," examined the environmental effects and costs of stover collection from eight corn-soybean rotation and continuous corn systems in a watershed typical of the eastern Corn Belt. The comparisons were made by combining results from watershed and greenhouse gas computer simulation models and minimizing the cost of stover collection, to select which farming practices to use in an agricultural watershed.

 

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In their analysis, Gramig, Purdue agricultural and biological engineer Indrajeet Chaubey and graduate researchers Cibin Raj and Carson Reeling found that a continuous corn system - corn grown on the same land year after year - planted with conventional tillage and removing 52 percent of the stover from the field released the most greenhouse gas and soil sediment per acre: 3.5 tons and 1.1 ton, respectively. That same acre of land yielded 2.7 tons of stover.

If all the nitrogen contained in the stover that is removed must be replaced and there is more continuous corn cultivation, researchers found that greenhouse gas emissions from cropland may increase.

At the low end of the environmental impact scale, a no-till corn-soybean rotation where 38 percent of the stover was removed emitted 2.7 tons of carbon dioxide per acre and yielded 2 tons of stover.