Cultivation of biomass sorghum for second generation ethanol production

Sorghum (Sorghum bicolor L.) is a very interesting biofuel feedstock crop. With C4 photosynthesis and drought tolerance, it is suitable for cultivation in water limited environments and could be a key crop in a warmer and unpredictable global climate. Furthermore, sorghum can be used for ethanol production from both 1st and 2nd generation technologies (using sweet/grain genotypes or biomass genotypes, respectively). The potential use of commercial sorghum genotypes for the production of 2nd generation ethanol was investigated in a two year project in Northern Italy. Fields trials were carried out for two years in two locations on a selection of genotypes to optimize agronomical technique, identifying in particular the effect of plant density, irrigation, fertilization, time of harvesting on crop yield. Biomass compositions were analysed for all genotypes while ethanol yield was estimated on three genotypes at harvest and after conservation. Pretreatment, hydrolysis and fermentation were carried out with the innovative technology developed by Chemtex. Biomass yield was on average 22.6 Mg ha-1, with large differences among genotypes, environments and cultivation techniques so that extreme yield of 10.6 and 38.4 Mg ha-1 were measured. Percentage of fermentable sugars on dry matter in the genotypes under trial varied from 47% to 60%, and glucans were on average 63% of the fermentable sugars in both years. Average Klason lignin and acetyl content were, respectively, 12.8% and 1.7%. Biomass composition varied significantly among genotypes. The test carried out on biomass preserved by on field drying or silage showed that the latter method results in high ethanol yield reduction and is therefore not a suitable option for sorghum conservation. In general biomass sorghum can be considered an interesting crop for 2nd generation ethanol production. Keywords: Sorghum bicolor, 2nd generation ethanol, cultivation, processing, conservation.