Biomass yield, chemical composition and theoretical ethanol yield for different genotypes of energy sorghum cultivated on marginal land in China

Energy sorghum [Sorghum bicolor (L). Moench] is potentially of great significance for bioethanol production because of its high biomass and wide adaptability. In this study, a field experiment was conducted on a semiarid marginal land in Inner Mongolia (39°10′N, 109°53′E), China, to assess the effects of genotypes with similar growth duration and biomass yield levels on chemical composition and theoretical ethanol yield (TEY) in both leaves and stems of four genotypes each of sweet and biomass sorghum in 2013 and 2014. Among all varieties, no significant variation was observed in the biomass yield of leaf (1.81–2.55 Mg ha−1) and stem (3.73–4.87 Mg ha−1), which was relatively low due to the marginal land with low temperature conditions. By contrast, considerable variation was detected in soluble sugars, ash and hexose contents of leaves and stems among the sweet sorghum varieties over two years. Compared with the sweet type, biomass sorghum varieties exhibited significantly lower soluble sugars content but higher cellulose, hemicellulose, and lignin contents in both leaf and stem tissues, resulting in significantly lower hexose and higher pentose contents. Moreover, stems exhibited significantly higher total content of hexose and pentose (725.4 g kg−1) than leaves (642.3 g kg−1) across all varieties, leading to significantly higher TEY of stems than that of leaves. Despite the slightly higher TEY of sweet sorghum, biomass sorghum varieties exhibited particularly stable chemical components and TEY across both experimental years, resulting in greater potential for industrial bioethanol production in this study. Overall, varietal selection was effective in improving the biomass feedstock quality of energy sorghum for biochemical conversion. The findings of this study will help to facilitate industrial bioethanol production from dedicated bioenergy crops.