Abstract
Switchgrass (Panicum virgatum L.), a warm-season perennial grass, is an important bioenergy crop candidate because it produces high biomass yields on marginal lands and on reclaimed surface mined sites. In companion studies, dry matter (DM) yields for Cave-in-Rock, Shawnee, and Carthage cultivars varied from 4.2 to 13.0 Mg ha−1averaged over 6 years at the reclaimed Hampshire site, and fertilization increased yields of Cave-in-Rock at Black Castle and Coal Mac sites from 0.3 to 2 Mg ha−1 during the first 3 years. The objective of these experiments was to compare the impacts of cultivar and soil amendments on biomass quality and theoretical ethanol production of switchgrass grown on surface mines with differing soil characteristics. Biomass quality was determined for fiber, ash, lignin, digestibility, and carbohydrate contents via near-infrared reflectance spectroscopy, and carbohydrates were used to calculate theoretical ethanol yield (TEY; L Mg−1) and multiplied by biomass yield to calculate theoretical ethanol production (TEP; L ha−1). Cultivars at the Hampshire site did not differ in TEY and ranged from 426 to 457 L Mg−1. Theoretical ethanol production from Cave-in-Rock at Hampshire was 7350 L ha−1, which was higher than other cultivars because of its greater biomass production. This TEP was higher than in other studies which predicted 4000 to 5000 L ha−1. At the Black Castle and Coal Mac sites, fertilizer applications slightly affected biomass quality of switchgrass and TEY, but provided greater TEP as a function of increased yield. Similar to other findings, total switchgrass biomass production has more impact than compositional differences on TEP, so maximizing biomass production is critical for maximizing potential biofuel production. With appropriate soil substrates, fertilization, planning, and management, large areas of reclaimed surface mines can be converted to switchgrass stands to produce high biomass quality and yields to support a bioethanol industry.
Highlights
Switchgrass is a model crop for cellulosic ethanol because of high biomass production potential and compositional characteristics [8]
To determine compositional differences among three switchgrass cultivars in experiment 1, biomass samples were collected for near-infrared reflectance spectroscopy (NIRS) analysis from Hampshire, a site where annual biomass dry matter (DM) yields were up to 19 Mg ha−1
In spite of few to no differences among cultivars for theoretical ethanol yield (TEY) at Hampshire, Cave-in-Rock had significantly higher theoretical ethanol production (TEP) due to its higher biomass production compared to Shawnee and Carthage
Summary
Switchgrass is a model crop for cellulosic ethanol because of high biomass production potential and compositional characteristics [8]. Simple conversion calculations can be used to predict ethanol yield using the hexose (glucose, mannose, and galactose) and pentose (xylose and arabinose) sugars from hydrolyzed switchgrass biomass cell walls [6, 35]. Within-field variation and small changes in soil properties do not seem to affect switchgrass composition because individual fields are subject to similar temperatures, precipitation, and harvest management [29]. This is useful in practice because biorefineries can run fewer analyses of switchgrass if shipments come to the refinery from harvests of the same fields. Wet chemical analysis to determine carbohydrate characteristics of biomass samples is expensive and time-consuming. A second objective was to determine the effect of fertilizer applications on Cave-in-Rock switchgrass composition, TEY, and TEP from reclaimed surface mine sites
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