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BIOLOGICAL SCIENCES / AGRICULTURAL SCIENCES
Net energy of cellulosic ethanol from switchgrass
*U.S. Department of Agriculture–Agricultural Research Service, University of Nebraska, 314 Biochemistry Hall, P.O. Box 830737, Lincoln, NE 68583-0737; and Agricultural Economics Department, University of Nebraska, 314A Filley Hall, Lincoln, NE 68583-0922
Edited by Pamela A. Matson, Stanford University, Stanford, CA, and approved November 21, 2007 (received for review May 21, 2007)
Perennial herbaceous plants such as switchgrass (Panicum virgatum L.) are being evaluated as cellulosic bioenergy crops. Two major concerns have been the net energy efficiency and economic feasibility of switchgrass and similar crops. All previous energy analyses have been based on data from research plots (<5 m2) and estimated inputs. We managed switchgrass as a biomass energy crop in field trials of 3–9 ha (1 ha = 10,000 m2) on marginal cropland on 10 farms across a wide precipitation and temperature gradient in the midcontinental U.S. to determine net energy and economic costs based on known farm inputs and harvested yields. In this report, we summarize the agricultural energy input costs, biomass yield, estimated ethanol output, greenhouse gas emissions, and net energy results. Annual biomass yields of established fields averaged 5.2 -11.1 Mg·ha–1 with a resulting average estimated net energy yield (NEY) of 60 GJ·ha–1·y–1. Switchgrass produced 540% more renewable than nonrenewable energy consumed. Switchgrass monocultures managed for high yield produced 93% more biomass yield and an equivalent estimated NEY than previous estimates from human-made prairies that received low agricultural inputs. Estimated average greenhouse gas (GHG) emissions from cellulosic ethanol derived from switchgrass were 94% lower than estimated GHG from gasoline. This is a baseline study that represents the genetic material and agronomic technology available for switchgrass production in 2000 and 2001, when the fields were planted. Improved genetics and agronomics may further enhance energy sustainability and biofuel yield of switchgrass.
agriculture | bioenergy | biomass | biomass energy | greenhouse gas
Author contributions: M.R.S., K.P.V., R.B.M., and R.K.P. designed research; M.R.S., K.P.V., R.B.M., and R.K.P. performed research; M.R.S. and K.P.V. analyzed data; and M.R.S., K.P.V., R.B.M., and R.K.P. wrote the paper.
This article is a PNAS Direct Submission.
This article contains supporting information online at www.pnas.org/cgi/content/full/0704767105/DC1.
To whom correspondence should be addressed. E-mail: ken.vogel{at}ars.usda.gov
© 2008 by The National Academy of Sciences of the USA
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