Finding Balance: Agricultural Residues, Ethanol, and the Environment

Crop residues like wheat straw and corn stover—i.e. stalks and leaves—have been proposed as a sustainable feedstock for a “next-generation” cellulosic ethanol industry in the United States. However, use of agricultural residues should not be considered to have low environmental impacts simply because they are a by-product of an existing use of the land. Such residues currently replenish and protect soils on working agricultural lands, and their removal is unlikely to be sustainable unless accompanied by adoption of agricultural best management practices such as no-till production, cover crops, and precision fertilizer management.

Key Findings

1. Even moderate corn stover harvest increases erosion and depletes soil carbon on working lands.
2. The increased fertilizer application and increased erosion associated with harvest of corn stover leads to increased nutrient losses from the field, which will exacerbate critical surface and coastal water issues like the Gulf of Mexico’s “dead zone.”
3. A conversion to reduced tillage production can help protect against soil loss due to erosion, but it is relatively ineffective at protecting against the depletion of soil carbon.
4. Other best management practices such as winter cover crops are effective at capturing nutrients and replacing harvested residues as a source of soil enrichment, but are not widely used by farmers in practice.

Policy Recommendations

1. All federal and state policies providing support for biofuel production (such as the Renewable Fuels Standard and the Volumetric Ethanol Excise Tax Credit) should include environmental performance requirements that ensure the adoption of best management practices to offset the environmental impacts of feedstock production.
2. Federal biomass research programs should be fully funded. Both USDA and USDOE should invest greater resources into research on the long-term sustainability of using biomass and agricultural residues for biofuel production.
3. All projects receiving federal funds to explore crop use for biofuel production should be required to explicitly address the soil, water, and greenhouse gas implications of the new crop varieties or production methods.
4. USDA should increase investment in research on obstacles and opportunities for adoption of agricultural best management practices, particularly cover crops and conservation tillage, and support programs and/or policies to overcome them.
5. In federal evaluations of biomass availability, the criteria for “sustainable” residue supply systems must be broadened beyond a consideration of erosion to include other ecosystem services provided by agricultural land such as soil carbon sequestration and water quality considerations.