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Removing corn stover? Keep your soil intact

Jeff Caldwell 03/18/2013 @ 3:30pm Multimedia Editor for Agriculture.com and Successful Farming magazine.

A growing amount of corn stover's being removed from fields during or after harvest. But, the removal of that critical crop residue could be causing harm to your fields' future viability, The results of a new study show.

The potential danger is 2-fold; first, there's the potential increase in greenhouse gas emissions caused by the release of nutrients and accompanying carbon while the stalks are being removed from the field. Then, there's the loss of soil structures allowed by another tillage pass in the field.

"For a given crop rotation and tillage system, as we simulated an increase in the rate of stover removal we found an increase in loss of sediment from crop fields, an increase in greenhouse gas flux to the atmosphere and a reduction in nitrate and total phosphorus delivered to waterways," says Purdue University ag economist Ben Gramig. "While optimizing production to maximize stover harvest at the lowest possible cost may lead to a reduction in nutrients delivered to rivers and streams, this comes at the expense of increased soil erosion and greenhouse gas emissions."

As much as 3.5 tons of greenhouse gas and 1.1 ton of soil sediment per acre is lost from a field under conventional tillage when just over half the stover is removed, a process that nets around 2.7 tons of of the cellulosic ethanol feedstock, according to Gramig's research.

And, the study shows when the rate of stover removal picks up, so does the sediment and nutrient loss.

"For a given crop rotation and tillage system, as we simulated an increase in the rate of stover removal we found an increase in loss of sediment from crop fields, an increase in greenhouse gas flux to the atmosphere and a reduction in nitrate and total phosphorus delivered to waterways," Gramig says. "While optimizing production to maximize stover harvest at the lowest possible cost may lead to a reduction in nutrients delivered to rivers and streams, this comes at the expense of increased soil erosion and greenhouse gas emissions."

For now, Gramig says the best choice to cut down on potential nutrient and sediment loss in fields where extensive stover harvest is going to happen is to minimize tillage. No-till systems are best for the time-being, but more research needs to happen to identify other ways to keep the soil and fertilizer intact from year to year.

"Combining no-till with continuous corn cultivation when stover is removed was capable of slightly lower sediment loss than the baseline today without any stover removal," Gramig said. "Introducing cover crops or replacing nitrogen that is removed with stover at lower rates was not considered in our study but should further reduce environmental impacts. These practices require additional study and would involve offsetting costs and savings."

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Actual stover removal rates 03/20/2013 @ 2:39pm I work for POET-DSM Advanced Biofuels, which is building its first commercial cellulosic ethanol plant right now in Iowa. I just wanted to note that these removal rates are very far beyond what POET-DSM contracts with farmers. We contract for 1 ton of biomass per acre on average, which is 20-25% of the above-ground biomass in that area (vs taking more than half the stover as this research did). We have commissioned the U.S. Department of Agriculture and Iowa State University to conduct soil sustainability work for the last 5 years on our fields, and we share that data with the public. http://www.poet.com/resources/documents/IowaStateUniversity_Emmetsburg%20Soil%20Study_Report2011.pdf That research has demonstrated that at the lower removal rate, there are no erosion concerns. There is some minor nutrient replacement. This research is more a warning to those looking to strip the fields.

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