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United States Department of Agriculture

Agricultural Research Service

Research Project: Genetic Enhancement and Management of Warm-Season Species for Forage, Turf and Renewable Energy

Location: Crop Genetics and Breeding Research

Title: Harvest management of 'Tifton 85' bermudagrass for cellulosic ethanol production

Authors
item Knoll, Joseph
item Johnson, Jennifer -
item Lee, R. Dewey -
item Anderson, William

Submitted to: BioEnergy Research
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: March 12, 2014
Publication Date: March 25, 2014
Citation: Knoll, J.E., Johnson, J.M., Lee, R., Anderson, W.F. 2014. Harvest management of 'Tifton 85' bermudagrass for cellulosic ethanol production. BioEnergy Research. DOI: 10.1007/s12155-014-9449-1.

Interpretive Summary: Bermudagrass (Cynodon spp.) is a common perennial summer forage crop in the Southeastern USA that could also be used for production of cellulosic ethanol, which is produced from whole-plant biomass, rather than from starch. Bermudagrass does not produce as much biomass as some other species that are being studied as biomass crops, but it can be harvested during the summer months, unlike most of these other grasses. This could allow for a more steady supply of biomass for cellulosic ethanol refineries. This study was conducted at Midville, GA to assess biomass yields, nutrient utilization, and cellulosic ethanol production from bermudagrass. The crop was grown with or without irrigation, and harvested either once (fall), twice (midsummer and fall), or three times (June, midsummer, and fall) over two years (2010 and 2011). Irrigation did not affect biomass yields in 2010 when ample rain was received, but in 2011, which was much dryer, the two- and three-cut systems under irrigation out-yielded the other treatments. The concentrations of nitrogen (N), phosphorous (P), and potassium (K) in harvested biomass were slightly affected by irrigation, but the age of the crop and harvest timing had much larger effects on nutrient concentrations. Multiplying the biomass yield by nutrient concentration in the biomass allows us to calculate how much of a particular nutrient was removed by harvesting. Total N removal was greatest in the three-cut system under irrigation, particularly in 2011. Biomass fiber composition was also affected by harvest timing, but these data did not show correlations with ethanol yield as we would expect. Ethanol production was measured by a bench-scale procedure in which finely ground biomass was subjected to dilute sulfuric acid at high temperature (pretreatment), followed by enzymatic breakdown to sugars and fermentation to ethanol by yeast. This procedure is called simultaneous saccharification and fermentation, or SSF. Some variation in ethanol production was observed between harvest treatments. Under dryland production a single fall harvest appears to be the most economical system for producing cellulosic ethanol from bermudagrass. Under irrigation two cuts should be possible, one in summer and one in the fall. A three-cut system could yield slightly more biomass under irrigation, but much more N would be removed in the biomass, and would thus be less economical.

Technical Abstract: Bermudagrass (Cynodon spp.) is a common perennial summer forage crop in the Southeastern USA that could also be used for cellulosic ethanol. This study was conducted at Midville, GA to assess biomass yields, nutrient utilization, and cellulosic ethanol production from bermudagrass. The crop was grown with or without irrigation, and harvested either once, twice, or three times over two years (2010 and 2011). Irrigation did not affect dry matter (DM) yields in 2010, but in 2011 the two- and three-cut systems under irrigation out-yielded the other treatments. The concentrations of N, P, and K in harvested biomass changed with age of the crop and harvest timing, and to a lesser extent were affected by irrigation as well. Total N removal was greatest in the three-cut system under irrigation, particularly in 2011. Biomass neutral and acid detergent fiber concentrations (NDF and ADF) and in-vitro dry matter digestibility (IVDMD) were also affected by harvest timing, but these data did not show correlations with ethanol yield. Ethanol production was measured by subjecting biomass to dilute-acid pretreatment and simultaneous saccharification and fermentation (SSF) at bench-scale in the laboratory. Some variation in ethanol production was observed between treatments. Under dryland production a single fall harvest appears to be the most economical system for producing cellulosic ethanol from bermudagrass. Under irrigation two cuts should be possible, one in summer and one in the fall. A three-cut system could yield slightly more biomass under irrigation, but much more N would be removed in the biomass.

Last Modified: 9/22/2014
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