Lower nitrogen losses with perennial biofuel crops
Perennial
biofuel crops such as miscanthus, whose high yields have led them to be
considered an eventual alternative to corn in producing ethanol, are now shown
to have another beneficial characteristic -- the ability to reduce the escape
of nitrogen in the environment. In a 4-year University of Illinois study that
compared miscanthus, switchgrass, and mixed prairie species to typical
corn-corn-soybean rotations, each of the perennial crops were highly efficient
at reducing nitrogen losses, with miscanthus having the greatest yield.
"Our results clearly demonstrate that environmental nitrogen fluxes from
row-crop agriculture can be greatly reduced after the establishment of
perennial biofuel crops," said U of I postdoctoral research associate
Candice Smith."Because of the establishment variability, we were able to
compare annual row crops with perennial crops. Although in the first two years,
nitrate leaching remained high in the non-established miscanthus crop, once a
dense, productive crop was established in the second year of growth, nitrate
leaching in tile drainage quickly decreased."
Smith said
that this ability to reduce the loss of nitrogen into the environment will
prove to be greatly beneficial.
"Intensive
corn production with large fertilizer inputs leads to large losses of nitrogen
into the environment, both through gas emissions of nitrous oxide and leaching
of nitrate to surface waters through tile drainage systems," added Mark
David, U of I biogeochemist. "Nitrous oxide is a greenhouse gas, and
nitrate can contaminate drinking water supplies and leads to coastal ocean problems.
The hypoxic zone that forms each summer in the Gulf of Mexico is a result of
nitrate leaching from the tile-drained Corn Belt of the midwestern United
States -- a likely location for biofuel production," he said.
In the
study, funded by the Energy Biosciences Institute, miscanthus, switchgrass, and
mixed prairie species were compared against a typical corn-corn-soybean
rotation. Harvested biomass and nitrogen, nitrous oxide emissions, and nitrate
leaching in the mid-soil profile and through tile drainage lines were all
measured.
The
researchers found that the perennial crops quickly reduced nitrate leaching in
the mid-soil profile as well as from tile lines. "By year four each of the
perennial crops had small losses," Smith said. "Nitrous oxide
emissions also were much smaller in the perennial crops--including switchgrass,
which was fertilized with nitrogen, while prairie and miscanthus were not.
Overall, nitrogen levels were higher for the corn and soybean treatment as well
as switchgrass, but were lower for prairie and miscanthus. Prairie and
miscanthus levels were lower due to harvest of the plant biomass (and nitrogen)
each winter, with no fertilizer nitrogen additions to replace it, as occurred
in corn and switchgrass," she said.
David
added that the miscanthus and mixed prairie also had very wide
carbon-to-nitrogen ratios in the harvested material -- as much as 257 to 1 for
miscanthus. "Miscanthus efficiently moved nitrogen from leaves to root and
rhizome systems after the growing season, where it could be used again the next
year," David said. "The lower nitrogen level suggests that the small
amount of nitrogen removed by harvest in prairie and miscanthus came from the
large pool of soil nitrogen and/or nitrogen fixation. If the soil is the
source, this could lead to depletion of this resource without fertilization. If
microbial fixation supplied the nitrogen, this would be a more sustainable
input," he said.
David
said that although more research is needed to fully understand the nitrogen
cycle in these new and exciting biofuel crops such as miscanthus, results from
this study clearly show these crops have the potential to quickly and greatly
reduce nitrogen losses that have important environmental effects, while
providing a large biomass harvest.
"Reduced Nitrogen Losses after Conversion of Row Crop
Agriculture to Perennial Biofuel Crops" was published in an issue of the Journal of Environmental Quality. In
addition to Smith and David, Corey Mitchell, Michael Masters, Kristina
Anderson-Teixeira, Carl Bernacchi, and Even DeLucia contributed to the
research.
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Posted by Unknown
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