Biofuel: Major Net Energy Gain From
Jan 14, 2008 - ScienceDaily
|Switchgrass grown in this study
yielded 93 percent more biomass per acre and an
estimated 93 percent more net energy yield than
previously estimated in a study done elsewhere.
(Credit: Image courtesy of University of Nebraska-Lincoln)
Switchgrass grown for biofuel production
produced 540 percent more energy than needed to grow,
harvest and process it into cellulosic ethanol, according
to estimates from a large on-farm study by researchers
at the University of Nebraska-Lincoln.
Results from the five-year study involving
fields on farms in three states highlight the prairie
grass' potential as a biomass fuel source that yields
significantly more energy than is consumed in production
and conversion into cellulosic ethanol, said Ken Vogel,
a U.S. Department of Agriculture-Agricultural Research
Service geneticist in UNL's agronomy and horticulture
The study involved switchgrass fields
on farms in Nebraska, North Dakota and South Dakota.
It is the largest study to date examining the net
energy output, greenhouse gas emissions, biomass yields,
agricultural inputs and estimated cellulosic ethanol
production from switchgrass grown and managed for
"This clearly demonstrates that switchgrass
is not only energy efficient, but can be used in a
renewable biofuel economy to reduce reliance of fossil
fuels, reduce greenhouse gas emissions and enhance
rural economies," Vogel said.
The joint USDA-ARS and Institute of
Agriculture and Natural Resources study also found
greenhouse gas emissions from cellulosic ethanol made
from switchgrass were 94 percent lower than estimated
greenhouse gas emissions from gasoline production.
In a biorefinery, switchgrass biomass
can be broken down into sugars including glucose and
xylose that can be fermented into ethanol similar
to corn. Grain from corn and other annual cereal grains,
such as sorghum, are now primary sources for ethanol
production in the U.S.
In the future, perennial crops, such
as switchgrass, as well as crop residues and forestry
biomass could be developed as major cellulosic ethanol
sources that could potentially displace 30 percent
of current U.S. petroleum consumption, Vogel said.
Technology to convert biomass into cellulosic ethanol
is being developed and is now at the development stage
where small commercial scale biorefineries are beginning
to be built with scale-up support from the U.S. Department
This study involved 10 fields of 15
to 20 acres each with four in Nebraska near Atkinson,
Crofton, Lawrence and Douglas; four in South Dakota
near Highmore, Bristol, Huron and Ethan; and two in
North Dakota near Streeter and Munich. Trials began
in 2000 and 2001 and continued for five years. Farmers
were paid for their work under contract with UNL and
documented all production operations, agricultural
inputs and biomass yields. The researchers used this
information to determine the net energy estimates.
Switchgrass grown in this study yielded 93 percent
more biomass per acre and an estimated 93 percent
more net energy yield than previously estimated in
a study done elsewhere of planted prairies in Minnesota
that received low agricultural inputs, Vogel said.
The study demonstrates that biomass energy from perennial
bioenergy crops such as switchgrass can produce significantly
more energy per acre than low input systems. Less
land will be needed for energy crops if higher yields
can be obtained.
Researchers point out in the study that
plant biomass remaining after ethanol production could
be used to provide the energy needed for the distilling
process and other power requirements of the biorefinery.
This results in a high net energy value for ethanol
produced from switchgrass biomass. In contrast, corn
grain ethanol biorefineries need to use natural gas
or other sources of energy for the conversion process.
In this study, switchgrass managed as
a bioenergy crop produced estimated ethanol yields
per acre similar to those from corn grown in the same
states and years based on statewide average grain
"However, caution should be used in
making direct ethanol yield comparisons with cellulosic
sources and corn grains because corn grain conversion
technology is mature, whereas cellulosic conversion
efficiency technology is based on an estimated value,"
Vogel said he does not expect switchgrass
to replace corn or other crops on Class 1 farm land.
He and his colleagues are developing it for use on
marginal, highly erodible lands similar to that currently
in the Conservation Reserve Programs. All the fields
in this study met the criteria that would have qualified
for this program. Using a conservation cellulosic
conversion value, researchers found that switchgrass
grown on the marginal fields produced an average of
300 gallons of ethanol per acre compared to average
ethanol yields of 350 gallons per acre for corn for
the same three states.
The researchers point out that this
was a base-line study. The switchgrass cultivars used
in this study were developed for use in pastures.
New higher yielding cultivars are under development
for specific use in bioenergy production systems.
Switchgrass yields continue to improve,
Vogel said. Recent yield trials of new experimental
strains in the three states produced 50 percent higher
yields than achieved in this study.
"Now, we really need to use an Extension
effort to let farmers know about this new crop," Vogel
Richard Perrin, UNL agricultural economist,
was the primary economic analyst for this study. Other
authors were Marty Schmer, USDA-ARS agricultural science
research technician and UNL doctoral student, and
Robert Mitchell, USDA-ARS agronomist at UNL.
Decades of switchgrass research at UNL
put scientists in the position to start studying the
crop as a biomass energy source in 1990.
"UNL and the USDA-ARS have been pioneers
in switchgrass research since the 1930s, domesticating
it as a pasture grass,"Vogel said.
Vogel has led research to develop switchgrass
cultivars for biomass production. The UNL-USDA team
also has developed recommendations for how best to
manage switchgrass to maximize biomass yields.
Future research will include further
studies of improving management practices including
work on improving establishment and harvesting methods,
improving biomass yield, and improving conversion
efficiency and net and total energy yields, Vogel
Switchgrass in this study employed UNL's
best management practices for switchgrass, including
no-till seeding, herbicides, weed control and adaptive
cultivars. This study was also based on farm fields
up to 20 acres instead of smaller research-scale plots
typically less than about 100 square feet.
Six cellulosic biorefineries that are
being co-funded by the U.S. Department of Energy also
are in the works across the U.S. that should be completed
over the next few years. These plants are expected
to produce more than 130 million gallons of cellulosic
ethanol per year, according to the U.S. Department
Researchers reported their findings
in the Proceedings of the National Academy of Sciences
Adapted from materials provided
by University of Nebraska-Lincoln.