By Scott Jamieson
Oct 25, 2011, West Lafayette, Ind - Purdue University researchers are studying how poplars might be turned into cellulosic ethanol in a large-scale field trial.
In May a
team of researchers led by Rick Meilan, associate professor of forestry
and natural resources, began a five-year study to determine the
viability of poplar species as an ethanol feedstock and cash crop for
Indiana farmers. The study includes trial plots at Pinney-Purdue
Agricultural Center east of Valparaiso and Southwest-Purdue Agricultural
Center just north of Vincennes.
Findings from the research could help propel the fledgling cellulosic ethanol industry, Meilan said.
biofuel production we're principally using the sugars in corn that are
fermented to produce alcohol that's then blended with petroleum
products," he said. "What we'd like to do is use cellulosic feedstocks,
including not just corn stover but also wood chips."
considered the next frontier in ethanol production. The process
involves extracting sugars from the cell walls of plant material, or
what is commonly known as biomass. Because most plants contain so much
more biomass than grain, cellulose potentially could provide more
ethanol than grain. With trees, the biomass volume is even larger than
it is with most row crops.
The Purdue study is looking at 69
varieties of poplar species within the genus Populus and how they
perform under different soil and climatic conditions, disease and insect
pressure, and fertilization and watering regimes. The varieties all are
cottonwoods, not tulip tree or yellow poplar, which aren't true
Poplars are already used in energy production. Wood is
burned at some power plants to create steam to turn turbines for
generating electricity. Meilan said the trees also offer advantages over
other species as a cellulosic ethanol feedstock.
is that poplars can be vegetatively propagated," he said. "That is, we
can take a stem segment and just shove it into the ground and it will
spontaneously produce roots in the portion of the stick that's beneath
the ground, and buds above ground will lead to the production of leaves
At both Purdue research farms, Meilan's team
hand-planted about 2,000 poplar sticks on three-acre tracts. The sticks
measured about 8 inches long and three-eighths inch in diameter.
advantage is that these trees are so efficient at photosynthesis,"
Meilan said. "They are capable of very rapid growth. We have some
varieties that, when fertilized and irrigated, are capable of growing up
to 15 feet a year in other locales. Some harvested trees are 90 feet
tall at 6 years of age."
By early October some of the trees at Pinney-Purdue and Southwest-Purdue already were more than 15 feet tall.
poplars are a multiyear crop, they might not be as management-intensive
as annual crops such as corn and soybeans, Meilan said. With a
multiyear crop the ground isn't disturbed each year by planting and
harvesting. And unlike row crops, poplars could be harvested at any time
of the year and sent directly to ethanol plants, allowing growers to
avoid drying and storage.
Meilan hopes Purdue research also can
address three challenges to growing poplar as an ethanol feedstock:
removing the sugars from cell walls and large-scale planting and
Extracting sugar from cellulose is more difficult
than it is with grain because of the presence of lignin, an organic
polymer within the cell walls of biomass. Sugars must be separated from
lignin before being converted into alcohol. Meilan is working with other
Purdue researchers to develop genetically modified poplar varieties
that have altered lignin composition and content.
Purdue researcher Patrick T. Murphy of the Department of Agricultural
and Biological Engineering are tackling the planting and harvesting
issues. Meilan believes it might be possible to modify conventional farm
machinery to conduct harvesting operations without requiring farmers to
make sizable investments in new equipment. Harvest would involve
cutting down trees a few inches above the ground. New trees then would
grow from the stems.
"If specialized equipment is needed for
harvest, maybe the farmer will only be responsible for growing the crop
and will, in turn, hire a contractor to come in and do the harvesting,"
Meilan said. "A lot of that goes on right now with corn."
Cellulosic ethanol production is not far away, Meilan said. Whether poplar will be part of the mix is uncertain.
are two important criteria when evaluating a potential bioenergy crop,"
he said. "One is how much biomass it produces. The other, which is
equally important, is how efficiently the sugars contained in the
biomass can be converted into fuel. As the technology develops it will
become even more profitable for growers."
partnered with Purdue on the poplar research. ArborAmerica Inc. of West
Point and GreenWood Resources Inc. of Portland, Ore., donated poplar
sticks, while Hoosier Energy of Bloomington provided financial support.