More Sustainable Feedstock for Ethanol

Picture: Researcher Gregg Sanford stands before a plot of giant miscanthus at Arlington.

Gregg-Sanford

Perennial crop yields can compete with corn stover, study suggests
By Mark E. Griffin

A six-year Great Lakes Bioenergy Research Center (GLBRC) study on the viability of different bioenergy feedstocks recently demonstrated that perennial cropping systems such as switchgrass, giant miscanthus, poplar, native grasses and prairie can yield as much biomass as corn stover.

The study is significant for addressing one of the biofuel industry’s biggest questions: Can environmentally beneficial crops produce enough biomass to make their conversion to ethanol efficient and economical?

Since 2008, research scientists Gregg Sanford and Gary Oates, based in the lab of CALS agronomy professor Randy Jackson, have worked with colleagues at Michigan State University (MSU) to cultivate more than 80 acres of crops with the potential to become feedstocks for so-called “second-generation” biofuels, that is, biofuels derived from non-food crops or the nonfood portion of plants. They’ve grown these crops at the CALS-based Arlington Agricultural Research Station and at MSU’s Kellogg Biological Station.

“We understand annual systems really well, but little research has been done on the yield of perennial cropping systems as they get established and begin to produce, or after farmland has been converted to a perennial system,” says Oates.

To find out basic information about how well certain crops produce biomass, Sanford and Oates tested the crops across two criteria: diversity of species, and whether a crop grows perennially (continuously, year after year) or annually (needing to be replanted each year).

Highly productive corn stover has thus far been the main feedstock for second-generation biofuels. And yet perennial cropping systems, which are better equipped to build soil quality, reduce runoff, and minimize greenhouse gas release into the atmosphere, confer more environmental benefits.

Corn, when grain is included, proved to be most productive over the first six-year period of the study at the Wisconsin site, but giant miscanthus, switchgrass, poplar and native grasses were not far behind. At the MSU site, where soil is less fertile, miscanthus actually produced the same amount of biomass as corn (grain included) in the experiment, with poplar and switchgrass within range.

“All of this means that, at large scales and on various soils, these crops are competitive with corn, the current dominant feedstock for ethanol,” Sanford says.

Now in the midst of the study’s eighth year, Sanford says the study will continue for the foreseeable future.

“We know that perennial systems can prevent negative impacts such as soil erosion and nitrate leaching, and that they also provide habitat for native species that provide beneficial ecosystem services,” Sanford says. “But there are still a lot of questions we want to answer about soil processes and properties— questions that take many years to answer.”