Building an ethanol industry that relies on corn stover - the leaves and stalks that remain behind when corn grain has been harvested - will require increased investments in research of a variety of farming practices.
“Corn stover is sometimes thought of as agricultural waste, but it serves an important function when left on the field. Increasing harvest of stover has the potential to exacerbate soil erosion, reduce surface-water quality, and increase agriculture-related greenhouse gas emissions that cause global warming,” said Liz Marshall, lead author of a report released today by the World Resources Institute.
Corn Stover for Ethanol Production: Potential and Pitfalls analyzes the potential impact on both soil erosion and greenhouse gas emissions from the agricultural sector when corn stover is removed and used to produce biofuels. Corn stover removal results in increased GHG emissions through both the loss of agricultural carbon sequestration capacity and increased use of fertilizer necessary to replace nutrients removed from the field with stover.
“It is becoming increasingly difficult to justify support of the biofuels industry without assurances that the biofuels produced achieve policy objectives without unacceptable soil, water, and air side effects,” Marshall added. “Environmental safeguards should be required for participation in any government programs that provide incentives for ethanol industry growth.”
Federal policies already exist that should be revisited and revised, including the Volumetric Ethanol Excise Tax Credit (VEETC) and the revised Renewable Fuel Standard, passed as part of the Energy Independence and Security Act of 2007. Any new and proposed policies should also include such safeguards.
Corn stover’s use as a feedstock for biofuels production is promising because of the existing corn production infrastructure. The fact that it is a residue of an existing use of the land means there is less competition between land allocated to food versus fuel crops, and it places less pressure on agriculture to expand its use of acreage to produce fuel crops. However, its use has environmental drawbacks because leaving corn stover on the field helps replenish soil carbon and control erosion. The report notes that further research is needed to determine the feasibility and costs of replacing the ecosystem services that could be threatened by large-scale removal of corn stover for biofuels production.
“Even moderate harvest of residues like corn stover for ethanol use threatens to significantly increase erosion and emissions of greenhouse gases from the agricultural sector when looking at the national level,” Marshall said.
Many farm production practices exist that can help control some of the negative impacts of stover removal, including reduced intensity of tillage, more precise and customized application of fertilizer, and the introduction of winter cover crops to replace the stover and perform its role as erosion protection and soil supplement. However, the WRI analysis suggests that the current system of government incentives is not sufficient to induce farmers to voluntarily adopt such practices in conjunction with stover harvest. Additional incentives or requirements will likely be needed to ensure that stover harvest is accompanied by the changes in farm production that are necessary to protect against negative side effects of harvest.
Cellulosic feedstocks, including corn stover, are projected to be on the commercial market within three to five years. The U.S. Department of Agriculture and Department of Energy have suggested that with aggressive breeding and technology advancement, corn stover could supply the energy equivalent of 9-14 percent of our current gasoline use at stover harvest rates that avoid significant increases in soil erosion. WRI’s analysis finds these numbers highly optimistic and notes that carbon emissions were not analyzed in the government’s 2005 study.
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