A team of investigators have found that the giant perennial grass Miscanthus x giganteus outperforms current biofuel sources. Using Miscanthus as a feedstock for ethanol production in the U.S. would reduce the acreage dedicated to biofuels while meeting government production goals, they report.
The findings, from researchers at the University of Illinois, appear this month in the journal Global Change Biology. Crop sciences professor Stephen P. Long, Ph.D., led the study and is also the editor of Global Change Biology.
“What we’ve found with Miscanthus is that the amount of biomass generated each year would allow us to produce about two and a half times the amount of ethanol we can produce per acre of corn,” says Dr. Long, who is also the deputy director of the BP-sponsored Energy Biosciences Institute, a multiyear, multiinstitutional initiative aimed at finding low-carbon or carbon-neutral alternatives to petroleum-based fuels.
Using corn or switchgrass to produce enough ethanol to achieve the White House’s goal of a 20% offset in gasoline use would take 25% of current U.S. cropland out of food production, according to the scientists. Getting the same amount of ethanol from Miscanthus, however would require 9.3% of current agricultural acreage, they add.
Switchgrass, which like Miscanthus is a perennial grass, requires fewer chemical and mechanical inputs than corn. In trials across Illinois, however, switchgrass produced only about as much ethanol feedstock per acre as corn, Dr. Long says.
“One reason why Miscanthus yields more biomass than corn is that it produces green leaves about six weeks earlier in the growing season,” Dr. Long explains. Miscanthus also stays green until late October in Illinois, while corn leaves wither at the end of August.
The growing season for switchgrass is comparable to that of Miscanthus but it is not nearly as efficient at converting sunlight to biomass, according to Frank Dohleman, a graduate student and co-author on the study.
A common criticism against using any biomass as a biofuel source is that plants are not very efficient, Dr. Long notes. They achieve about 0.1% efficiency of conversion of sunlight into biomass, he adds. “What we show here is on average Miscanthus is in fact about 1 percent efficient.”
Field trials also showed that Miscanthus is tolerant of poor soil quality, Dr. Long reports. “Our highest productivity is actually occurring in the south, on the poorest soils in the state. So that also shows us that this type of crop may be very good for marginal land or land that is not even being used for crop production.”
Using Miscanthus in an agricultural setting has not been without its challenges, Dr. Long concedes. Because it is a sterile hybrid, it must be propagated by planting underground stems, or rhizomes. This was initially a laborious process, Dr. Long points out, but mechanization allowed his team to plant about 15 acres a day. In Europe, where Miscanthus has been grown for more than a decade, patented farm equipment can plant about 50 acres of Miscanthus rhizomes a day, he adds.
Companies have begun to propagate Miscanthus rhizomes for commercial sale, Long says. Although research has led to improvements in productivity and growers are poised to begin using it as a biofuels crop on a large scale, Miscanthus is in its infancy as an agricultural product, he continues.
“Keep in mind that this Miscanthus is completely unimproved, so if we were to do the sorts of things that we’ve managed to do with corn, where we’ve increased its yield threefold over the last 50 years, then it’s not unreal to think that we could use even less than 10 percent of the available agricultural land.”