Screening for biofuel feedstock quality of perennial warm-season grasses in semiarid subtropical environments

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A Screening for Biofuel Feedstock Quality of Perennial
Warm-Season Grasses in Semiarid Subtropical Environments
Research Report 774
L.M. Lauriault, M.A. Marsalis, S.V. Angadi, F.E. Contreras-Govea,
D.R. Dreesen, and D.M. VanLeeuwen1
Agricultural Experiment Station • College of Agricultural, Consumer and Environmental Sciences
ABSTRACT
Cellulosic biofuel crops have not been evaluated for semiarid, subtropical environments, but commonly grown, taller-growing, perennial warm-season grasses may have merit. Desirable quality components [low crude protein (CP; <3.3%), low ash, high neutral de­tergent fiber (NDF), and high in vitro true digestibility (IVTD)] were estimated by near infrared spectroscopy (NIRS) for two replicates of 16 perennial warm-season grasses collected in eastern New Mexico post-frost in 2007 and 2008. Switchgrass (Panicum virgatum), which is the model perennial warm-season grass crop for cel­lulosic biofuel production, averaged 0.98, 6.83, 76, and 56.7% CP, ash, NDF, and IVTD, respectively. When averaged across years, big, little, and silver bluestem [Andropogon gerardii Vitman, Schizachyrium scoparium (Michx.) Nash, and Bothriochloa laguroides D.C., respec­tively]; Indiangrass [Sorghastrum nutans (L.) Nash]; and switchgrass had observed values that were in a desirable range, with CP consistently below 3.3%. Cane and yel­low bluestem [B. barbinodis (Lag.) Herter and B. isch­aemum, respectively], giant spike dropseed (Sporobolus contractus Hitch. or S. giganteus Nash), Kleingrass (P. coloratum), vine mesquite (P. obtusum H.B.K), and weeping lovegrass [Eragrostis curvula (Schrad.) Nees] had CP values both above and below 3.3%, but had desir­able values for ash, NDF, and IVTD. Giant sacaton and sand dropseed (S. wrightii Scribn. and S. cryptandrus Torr., respectively) had high CP, but were acceptable for the other components. High average CP and ash in plains bristlegrass [Setaria leucopila (Scribn. & Merr.) K. Schum.], purple threeawn (Aristida purpurea Nutt.), and sideoats grama [Bouteloua curtipendula (Michx.) Torr.] and low NDF for plains bristlegrass and sideoats grama lessen their value for cellulosic biofuel feedstock despite their fairly high IVTD. Several perennial warm-season grasses commonly grown in semiarid, subtropical re­gions may have potential as cellulosic biofuel feedstock. Further testing is needed to evaluate yield potential and to formally compare biofuel feedstock quality compo­nents in low-input systems.
INTRODUCTION
A goal throughout much of the developed world is to replace a considerable portion of petroleum fuel with biofuels, including those from cellulosic biomass sources (U.S. Department of Energy, 2006). Plant species that are more water-use efficient are preferred, and biofuel crops will be needed for each specific environment (Shu­bert, 2006). Cellulosic biomass crops have been identi­fied for most agro-ecoregions as defined by temperature, rainfall, and soil types, but few have been identified for semiarid, subtropical regions, such as the Southern High Plains of the USA, which is dominated by short, mixed, and tallgrass prairie (U.S. Department of Energy, 2006; Allen et al., 2008).
Perennial warm-season grasses are ideally suited for biomass production because they can generally be har­vested after seed production and senescence to optimize yield and cellulosic biofuel feedstock quality. This strat­egy also reduces energy and labor costs for harvesting and curing (Muir et al., 2001; Xiong et al., 2008) and improves feedstock quality through nutrient redistri­bution from aboveground plant parts to belowground plant parts (Mulkey et al., 2006; Parrish et al., 2008; Xiong et al., 2008).
These grasses also tend to be lower than some other forage species in crude protein (CP) and ash and higher in fiber and digestibility, which are desirable for bio­fuel feedstock (Sanderson et al., 1999; Mulkey et al., 2006; Parrish et al., 2008) and are already measured as components of forage nutritive value for livestock feed (Geber, 2002). Wolfrum and Sluiter (2008) found that near infrared spectroscopy (NIRS) estimates of fiber were highly correlated with wet chemistry evaluations
1Respectively, Forage Agronomist, Agricultural Science Center at Tucumcari, New Mexico State University (New Mexico State University Agricultural Science Center, 6502 Quay Rd AM.5, Tucumcari, NM 88401, USA; Telephone: 1-575-461-1620; Fax: 1-575-461-1631; Email: lmlaur@nmsu.edu); Extension Agrono­my Specialist, Agricultural Science Center at Clovis, NMSU; Crop Physiologist, Agricultural Science Center at Clovis, NMSU; Agronomist, Agricultural Science Center at Artesia, NMSU; Agronomist, USDA-NRCS Plant Materials Center, Los Lunas, NM; and Professor, NMSU Agricultural Biometrics Service, NMSU.