December 8, 2006
Fuels made from prairie biomass
reduce carbon dioxide levels in atmosphere
Diverse mixtures of native prairie
plant species have emerged as a leader in the quest to identify
the best source of biomass for producing sustainable, bio-based
fuel to replace petroleum.
A new study led by David Tilman, an ecologist at the
University of Minnesota, shows
that mixtures of native perennial grasses and other flowering
plants provide more usable energy per acre than corn grain
ethanol or soybean biodiesel and are far better for the
environment. The research was supported by the
National Science Foundation
(NSF) and the University of Minnesota Initiative for Renewable
Energy and the Environment.
"Biofuels made from high-diversity mixtures of prairie plants
can reduce global warming by removing carbon dioxide from the
atmosphere. Even when grown on infertile soils, they can provide
a substantial portion of global energy needs, and leave fertile
land for food production," Tilman said.
The findings are published in the Dec. 8, 2006, issue of the
The is study based on 10 years of research at Minnesota's Cedar
Creek Natural History Area, one of 26 NSF long-term ecological
research (LTER) sites. It shows that degraded agricultural land
planted with diverse mixtures of prairie grasses and other
flowering plants produces 238 percent more bioenergy on average
than the same land planted with various single prairie plant
species, including switchgrass.
"This study highlights very clearly the additional benefits of
taking a less-intensive management approach and maintaining
higher biodiversity in the process," said Henry Gholz, NSF LTER
program director. "It establishes a new baseline for evaluating
the use of land for biofuel production."
Tilman and his colleagues estimate that fuel made from this
prairie biomass would yield 51 percent more energy per acre than
ethanol from corn grown on fertile land. Prairie plants require
little energy to grow and all parts of the plant above ground
Fuels made from prairie biomass are "carbon negative," which
means that producing and using them actually reduces the amount
of carbon dioxide (a greenhouse gas) in the atmosphere. Prairie
plants store more carbon in their roots and soil than is
released by the fossil fuels needed to grow and convert them
into biofuels. Using prairie biomass to make fuel would lead to
the long-term removal and storage of from 1.2 to 1.8 U.S. tons
of carbon dioxide per acre per year. This net removal of
atmospheric carbon dioxide could continue for about 100 years,
the researchers estimate.
In contrast, corn ethanol and soybean biodiesel are "carbon
positive," meaning they add carbon dioxide to the atmosphere,
although less than fossil fuels.
Switchgrass, which is being developed as a perennial bioenergy
crop, was one of 16 species in the study. When grown by itself
in poor soil, it did not perform better than other single
species and gave less than a third of the bioenergy of
"Switchgrass is very productive when it's grown like corn in
fertile soil with lots of fertilizer, pesticide and energy
inputs, but this approach doesn't yield as much energy gain as
mixed species in poor soil nor does it have the same
environmental benefits," said paper co-author Jason Hill, also
of the University of Minnesota.
To date, all biofuels, including cutting-edge nonfood energy
crops such as switchgrass, elephant grass, hybrid poplar and
hybrid willow, are produced as monocultures grown primarily in
The researchers estimate that growing mixed prairie grasses on
all of the world's degraded land could produce enough bioenergy
to replace 13 percent of global petroleum consumption and 19
percent of global electricity consumption.
The practice of using degraded land to grow mixed prairie
grasses for biofuels could provide stable production of energy
and have additional benefits, such as renewed soil fertility,
cleaner ground and surface waters, preservation of wildlife
habitats, and recreational opportunities.
The National Science Foundation
(NSF) is an independent federal agency that supports fundamental
research and education across all fields of science and
engineering, with an annual budget of $5.58 billion. NSF funds
reach all 50 states through grants to nearly 1,700 universities
and institutions. Each year, NSF receives about 40,000
competitive requests for funding, and makes nearly 10,000 new
funding awards. The NSF also awards over $400 million in
professional and service contracts yearly.