Lignocellulosic Theoretical Ethanol Production of Potential Bioenergy Sorghum Genotypes.

The lignocellulosic ethanol yield of a feedstock is dependent on both biomass yield and compositional characteristics. Sorghum bicolor (L.) Moench have been bred to have genotypes with contrasting compositions. The objective of this study was to evaluate the influence of stover composition differences on overall theoretical ethanol yield of differing sorghum genotypes. Composition differences were analyzed within each genotype by N application rate and environment. The trade-off between lignin content and ethanol yield were also discussed based on N application rate. Five sorghum (Sorghum bicolor (L.) Monech genotypes; commercial, sweet, photoperiod sensitive, forage and forage with BMR trait sorghums,  and a maize hybrid (Zea mays L.) control were evaluated for grain and stover yield and stover composition over four N application rates (0, 67, 135, and 202 kg N ha^-1) over two years  (2008 and 2010) locations. Grain and stover theoretical ethanol yield was estimated by using standard industry based stoichiometric conversion ratios to hexose and pentose sugars converted from non-structural sugars and starches and hemicellulose and cellulose which were determined from post-harvest analyses. Lignin and ash concentrations were also determined in the same way. A two-way ANOVA and regression analysis were used to interpret the effects of genotype, N- application rate, and environment on above ground composition and TEY. Sorghum genotypes varied in concentration of total non-structural sugars but showed no significant difference in fibers. However there were significant differences in total content of sugars and fibers in the stover. Sorghum had lower lignin concentration and higher carbohydrate concentrations overall in comparison to maize. Nitrogen application rates did not have significant impact on of stover component concentration.