Lincoln, Nebraska
January 9, 2008
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 highlights 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 department.
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
biomass fuel.
"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.
Researchers reported their findings in this week's (Jan.7-11)
Proceedings of the National Academy of Sciences. The research
paper is available online.
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 U.S.
ethanol production.
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 of Energy.
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 their 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 yields.
"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.
Vogel said that 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 stains 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 said.
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
said.
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 of
Energy. |
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