Biomass yield and changes in chemical composition of sweet sorghum cultivars grown for biofuel

This investigation was carried out in order to evaluate changes in biomass, carbohydrates, and calculated ethanol yield (CEY) from anthesis to 40 days after anthesis (DAA) of five sweet sorghum (Sorghum biocolor (L.) Moench) cultivars with a crop cycle length of 111–165 days in Beijing (39°56′N, 116°20′E). Aboveground dry weight (AGDW) and total soluble sugar yield (TSSY, 1.3–10.5 t ha−1) increased with time after anthesis and with crop cycle length. Cellulose and hemicellulose contents at anthesis varied between 205–277 g kg−1 and 187–232 g kg−1, respectively, and were significantly (p < 0.05) higher than either 20 DAA or 40 DAA. Cellulose and hemicellulose yields changed between 1.6 and 6.6 t ha−1 from anthesis to 40 DAA. The stems comprised major sinks of soluble sugar, with 79.4–94.6% of TSSY, and major sinks of insoluble sugar, with 55.9–75.9% of the total cellulose and hemicellulose yield. The hybrids exhibited higher TSSY, cellulose, hemicellulose and grain yield, and therefore also CEY than the inbred cultivars with a similar crop cycle length. Total CEY from the carbohydrates increased with time after anthesis and with crop cycle length, ranging between 4867 and 13032 L ha−1 on 40 DAA during the two years. It is concluded that the effects of each factor of year, harvest time, and genotype on biomass, carbohydrates yield, and CEY are highly significant. The interaction of genotype with year (environment) has significant effects on the total CEY. We recommend beginning the harvest of sweet sorghum upon the early maturity of the cultivars from around 20 DAA. This will result in a harvest period of around two months until grain maturity of the late cultivars for ethanol production in North China.