John Maxwell grows corn south of Nevada, IA, and has been working with DuPont since 2012 to study the sustainable harvest of corn stover as a cellulosic ethanol feedstock. In a webinar on cellulosic ethanol supply chains hosted by Biofuels Digest  this week, Maxwell cited several agronomic benefits of removing corn stover: reducing tillage (and associated labor and fuel costs), warming the soil for spring planting, reducing the number of overwintering insects and improving corn yield. Maxwell added that he applies hog manure on the corn to improve organic matter levels.
Maxwell and other corn growers in north central Iowa will be supplying corn stover to the DuPont Industrial Bioscience biorefinery in Nevada, IA. John Pieper, corn stover feedstock workstream lead, DuPont, said that the facility (which will have a nameplate capacity of 30 million gallons per year when construction is completed) will annually collect 375,000 tons of corn stover from approximately 190,000 acres. This represents about 25 percent of the corn acres within a 30-mile radius of Nevada.
Andy Hegenstaller, agronomic research manager, DuPont Pioneer, showed the accompanying chart, which illustrates how much cover stover should be retained in fields to prevent soil erosion from exceeding tolerable levels. This chart (developed from several years of USDA studies) also shows that tillage practices and crop rotation both have significant effects on how much stover can be harvested sustainably.
A two-ton per acre stover harvest would be sustainable for continuous corn production. Most of Maxwell’s production is currently corn-on-corn on relatively flat ground. In a corn-soybean rotation, Hegenstaller said that the frequency of stover harvest should be reduced.
Hegenstaller pointed out that fields averaging 170 bushels of corn per acre would produce about four tons of stover per acre. Fields averaging 210 bushels per acre would produce about five tons per acre, and fields producing as high as 295 bushels of corn per acre would translate to about seven tons per acre.
Tillage is currently the primary means of residue management. By collecting corn stover, growers could eliminate or greatly reduce tillage. Forty percent of the farmers in the DuPont stover collection program reduced their tillage intensity last year or were expected to do this year.
DuPont and Iowa State University studied eight Iowa fields in 2012 and six fields in 2013. They found that partial (~ 50 percent) corn stover removal improved corn yields by about 5.2 bushels per acre in more than 90 percent of the fields.
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