ARS | Publication request: Temporal and spatial variation in switchgrass biomass composition and theoretical ethanol yield

Submitted to: Agronomy Journal
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: October 7, 2011
Publication Date: November 23, 2011
Citation: Schmer, M.R., Vogel, K.P., Mitchell, R., Dien, B.S., Jung, H.G., Casler, M.D. 2012. Temporal and spatial variation in switchgrass biomass composition and theoretical ethanol yield. Agronomy Journal. 104:54-64.

Interpretive Summary: Switchgrass is a perennial grass that is being developed as a bioenergy feedstock for the United States. Switchgrass will likely be converted into biofuels to meet growing transportation fuel demands. We collected switchgrass samples from fields in North Dakota, South Dakota, and Nebraska to determine cell wall components that will be converted to ethanol using near-infrared reflectance spectroscopy technology. We then estimated the potential ethanol yield from individual fields. In addition we compared theoretical yield with switchgrass biomass yield from each field to estimate the amount of ethanol produced per hectare. Results show that ethanol yields were variable across years and across fields which were partially caused by weather factors and management practices. Total theoretical ethanol production ranged from 420 to 887 gallons per acre across fields. Switchgrass biomass composition from farmer fields can be expected to have significant annual and field-to-field variation in a production region, and this variation will significantly affect ethanol or other liquid fuel yields per tonne or hectare. Cellulosic biorefineries will need to consider this potential variation in biofuel yields when implementing their biochemical conversion technology.

Technical Abstract: Information on temporal and spatial variation in switchgrass (Panicum virgatum L.) biomass composition as it affects ethanol yield (L Mg-1) at a biorefinery and ethanol production (L ha-1) at the field scale has previously not been available. Switchgrass biomass samples were collected from a regional, on-farm trial and biomass composition was determined using newly developed near-infrared reflectance spectroscopy (NIRS) prediction equations and theoretical ethanol yield (100% conversion efficiency) was calculated. Total hexose (cell wall polysaccharides and soluble sugars) concentration ranged from 342 g kg-1 to 398 g kg-1 while pentose (arabinose and xylose) concentration ranged from 216 g kg-1 to 245 g kg-1 across fields. Theoretical ethanol yield varied significantly by year and field, with 5 yr means ranging from 381 L Mg-1 to 430 L Mg-1. Total theoretical ethanol production ranged from 1749 L ha-1 to 3691 L ha-1 across fields. Variability (coefficient of variation) within established switchgrass fields ranged from 1% to 4% for theoretical ethanol yield (L Mg-1) and 14% to 38% for theoretical ethanol production (L ha-1). Most fields showed a lack of spatial consistency across harvest years for theoretical ethanol yield or total theoretical ethanol production. Switchgrass biomass composition from farmer fields can be expected to have significant annual and field-to-field variation in a production region, and this variation will significantly affect ethanol or other liquid fuel yields per tonne or hectare. Cellulosic biorefineries will need to consider this potential variation in biofuel yields when developing their business plans.