Stover refers to stalks, leaves and cobs that remain in corn fields after the grain harvest. Farmers leave it there to revitalize the soil and prevent erosion. Now, thanks to scientific and technological advances, farmers face the prospect of harvesting stover for cellulosic sugars that can be fermented into ethanol.
However, this presents a quandary, notes Wally Wilhelm, a plant physiologist in the Agricultural Research Service's (ARS) Agroecosystem Management Research Unit at Lincoln, Neb.
On the one hand, harvesting stover for sugars to make ethanol may lessen dependence on crude-oil imports. On the other hand, leaving stover in place may help prevent soil erosion caused by strong winds or intense rainfall. It also replaces lost nutrients and sequesters carbon in the soil, lessening CO2 accumulation in the atmosphere as a greenhouse gas and its contribution to global climate change.
This summer marks the second season of field studies under a five-year project that Wilhelm is coordinating to determine where, when and how much stover can be harvested for ethanol uses without harming the soil. His collaborators on the Renewable Energy Assessment Project (REAP), as it's called, include scientists from 12 other ARS locations, state universities and the U.S. Department of Energy.
For his part, Wilhelm has teamed with ARS Lincoln scientist Gary Varvel to conduct a 100-acre study on a privately run farm to examine the effect stover harvesting has on organic matter content, grain yield and carbon sequestration on high-, medium- and low-productivity soils.
Other REAP scientists include John Baker in St. Paul, Minn. There, together with colleagues, Baker is conducting experiments with winter cover crops and living mulches like kura clover to determine whether they could help maintain soil health and productivity when stover is harvested.
According to Wilhelm, REAP aims to establish stover-management guidelines that will help farmers, ethanol producers and action agencies strike a balance between environmental stewardship and bioenergy production needs.
ARS is the U.S. Department of Agriculture's chief scientific research agency.
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