Impact of harvest time and switchgrass cultivar on sugar release through enzymatic hydrolysis

Authors: Serapiglia, Michelle; Dien, Bruce; Boateng, Akwasi; Casler, Michael

Submitted to: BioEnergy Research
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 11/29/2016
Publication Date: 5/9/2017
Citation: Serapiglia, M., Dien, B.S., Boateng, A.A., Casler, M.D. 2017. Impact of harvest time and switchgrass cultivar on sugar release through enzymatic hydrolysis. BioEnergy Research. 10:377-387.

Interpretive Summary: Switchgrass is a promising bioenergy crop within the United States for biofuels production. Previously we reported that the time the switchgrass is harvested can have a significant effect on the biomass yield potential and the biomass quality of the crop. We found that delaying the harvest of switchgrass resulted in decreased yields of switchgrass biomass and reduced amounts of ash and nutrients in the biomass. The current study further evaluated how harvest time impacted changes in biomass composition and potential conversion of the biomass to ethanol. Delaying harvest until after a frost or allowing the biomass to over-winter and harvest in the spring resulted in an increase in the concentration of structural carbohydrates (cellulose and hemicellulose) and lignin content in the biomass. Conversely, delaying harvest time lowered the amounts of ash and soluble sugars present in the biomass. Delaying harvest until after frost improved ethanol production potential and the value of the harvested biomass. These results will be critical in improving management strategies for switchgrass bioenergy crops to maximize crop yields, biomass quality, and conversion potential.

Technical Abstract: Switchgrass (Panicum virgatum L.) is a native North American prairie grass being developed for bioenergy production in the central and eastern USA. The objective of this study was to identify the impacts harvest time and switchgrass cultivar had on sugar release variables determined through enzymatic hydrolysis. Previously we reported that delaying harvest of switchgrass until after frost and until after winter resulted in decreased yields of switchgrass but it reduced the amount of ash and nutrients in the biomass. The current study used near-infrared reflectance spectroscopy (NIRS) to broaden an existing set of calibration equations designed to predict composition and sugar release variables of switchgrass. These updated calibrations were then applied to the full set of samples from a multi-year and multi-location switchgrass harvest-management study. Composition and processor sugar yields were significantly affected by location, year, cultivar, and harvest date of which harvest date was the most important. Delaying the time of harvest until after frost or post-winter increased the concentration of structural carbohydrates from 500 g per kg to 570 g per kg in the biomass and lignin content from 160 g per kg to 200 g per kg. Conversely, delaying harvest time lowered the amounts of ash and soluble sugars. The later harvest dates also yielded more sugars following processing with yields increasing over 20% from the first harvest. Increased sugar yields are attributable to both increased concentration of sugars in the biomass upon harvest and reduced biomass recalcitrance. Based upon processed sugar yields, it is estimated that a biorefinery producing 20 million gal. of ethanol per year would require 229-373 square kilometers of land cultivated with switchgrass.