Miscanthus outperforms current biofuels sources — by a lot, say University of Illinois researchers.
Using the giant perennial grass as a feedstock for ethanol production in the U.S. could significantly reduce the acreage dedicated to biofuels while meeting government biofuels production goals, the researchers report.
Using corn or switchgrass to produce enough ethanol to offset 20% of gasoline use — a current White House goal — would take 25% of current U.S. cropland out of food production, according to the report. Getting the same amount of ethanol from miscanthus would require only 9.3% of current agricultural acreage.
“What we've found with miscan-thus is that the amount of biomass generated each year would allow us to produce about 2½ times the amount of ethanol we can produce per acre of corn,” says crop scientist Stephen Long, who led the study. Long is the deputy director of the BP-sponsored Energy Biosciences Institute, aimed at finding low-carbon or carbon-neutral alternatives to petroleum-based fuels.
In trials across Illinois, switchgrass, which like miscanthus requires fewer chemical and mechanical inputs than corn, produced only about as much ethanol feedstock per acre as corn, Long says.
“It wasn't that we didn't know how to grow switchgrass, because the yields we obtained were actually equal to the best yields that had been obtained elsewhere,” he says. Corn yields in Illinois are also among the best in the nation.
“One reason why miscanthus yields more biomass than corn is that it produces green leaves about six weeks earlier in the growing season,” Long says. It also stays green until late October in Illinois.
Switchgrass' growing season is comparable to that of miscanthus, but it is not as efficient at converting sunlight to biomass, Frank Dohle-man, a graduate student and study co-author, found.
“One of the criticisms of using any biomass as a biofuel source is it has been claimed that plants are not very efficient — about 0.1% efficiency of conversion of sunlight into biomass,” Long says. “On average, miscanthus is in fact about 1% efficient, so about 1% of sunlight ends up as biomass.”
Field trials also showed that miscanthus is tolerant of poor soil quality, Long says.
“Our highest productivity is actually occurring in the south, on the poorest soils in the state,” he says. “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.”
Miscanthus is not without its challenges, Long says. It's a sterile hybrid and must be propagated by planting rhizomes. Initially a laborious process, mechanization now allows the team to plant about 15 acres a day. In Europe, where it has been grown for more than a decade, patented farm equipment can plant about 50 acres of rhizomes a day, he says.
If harvested in December or January, after nutrients have returned to the soil, it requires little fertilizer.
At least a dozen companies are building or operating plants in the U.S. to produce ethanol from lignocellulosic feedstocks, the non-edible parts of plants, and companies are propagating miscanthus rhizomes for commercial sale, Long says.