Abstract
Field experiments were conducted in marginal lands, i.e., sub-humid climate and saline-land (SHS) and semi-arid climate and wasteland (SAW), to evaluate ethanol potential based on the biomass yield and chemical composition of biomass type (var. GN-2, GN-4, and GN-10) and sweet type (var. GT-3 and GT-7) hybrids of energy sorghum [Sorghum bicolor (L.) Moench] in comparison with sub-humid climate and cropland (SHC) in northern China. Results showed that environment significantly (p < 0.05) influenced plant growth, biomass yield and components, and subsequently the ethanol potential of energy sorghum. Biomass and theoretical ethanol yield of the crop grown at SHS (12.2 t ha−1 and 3,425 L ha−1, respectively) and SAW (8.6 t ha−1 and 2,091 L ha−1, respectively) were both statistically (p < 0.001) lower than values at the SHC site (32.6 t ha−1 and 11,853 L ha−1, respectively). Higher desirable contents of soluble sugar, cellulose, and hemicellulose were observed at SHS and SHC sites, while sorghum grown at SAW possessed higher lignin and ash contents. Biomass type sorghum was superior to sweet type as non-food ethanol feedstock. In particular, biomass type hybrid GN-10 achieved the highest biomass (17.4 t ha−1) and theoretical ethanol yields (5,423 L ha−1) after averaging data for all environmental sites. The most productive hybrid, biomass type GN-4, exhibited biomass and theoretical ethanol yields >42.1 t ha−1 and 14,913 L ha−1, respectively, at the cropland SHC site. In conclusion, energy sorghum grown on marginal lands showed a very lower ethanol potential, indicating a considerable lower possibility for being used as commercial feedstock supply when compared with that grown on regular croplands. Moreover, screening suitable varieties may improve energy sorghum growth and chemical properties for ethanol production on marginal lands.
Highlights
Industrial-scale cultivation of non-food energy crops for biofuels production is generally recognized as a positive step toward preventing energy shortages and decreasing greenhouse gas emissions (Qin et al, 2011; Sanscartier et al, 2014)
This study revealed environmental stress affecting biomass yield to guide future development of promising sorghum hybrids adapted to growth on marginal lands
As part of a larger sustainable agro-industrial framework, biomass type sorghum feedstock should be encouraged for industrial scale ethanol production due to its high productivity, adaptation to marginal growth conditions, and desirable qualities that facilitate efficient conversion of its biomass to ethanol
Summary
Industrial-scale cultivation of non-food energy crops for biofuels production is generally recognized as a positive step toward preventing energy shortages and decreasing greenhouse gas emissions (Qin et al, 2011; Sanscartier et al, 2014). As part of China’s comprehensive energy plan, its bioenergy industry is vigorously accelerating cellulosic ethanol fuel production and diversifying feedstock supplies to include new crops such as cassava and sweet sorghum. As part of the overall plan, biofuel feedstock production will be limited to marginal lands to avoid land-use competition with food crops to maintain greater food security (Zhuang et al, 2011). Energy sorghum, including biomass and sweet type varieties, has recently gained favor as bioethanol feedstock amongst numerous candidate crops (Rooney et al, 2007; Tew et al, 2008; Xie, 2012). Cellulosic biomass is optimally converted to ethanol when lignin content is low (Weng et al, 2008). High ash content may reduce efficiency of thermochemical conversion of biomass to fuel (Cassida et al, 2005)
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