Sweet sorghum as a bioenergy crop: Literature review

• Adaptation to diverse growing conditions is the virtue of sweet sorghum for bioenergy.
• Potential dedicated biomass–bioenergy crop with a slight effect on the food chain.
• It is a high net energy ratio crop with about 2 units recovered for each units used.
• Storage and transport of biomass to processing facilities remains the major hurdle.
• Developing perennial varieties may improve seasonality of biomass availability.

Sweet sorghum (Sorghum bicolor L. Moench) is a widely adapted sugar crop with high potential for bioenergy and ethanol production. Sweet sorghum can yield more ethanol per unit area of land than many other crops especially under minimum input production. Sweet sorghum is well-adapted to marginal growing conditions such as water deficits, water logging, salinity, alkalinity, and other constraints. Sweet sorghum potential exists for ethanol yield of 6000 L ha−1 with more than three units of energy attained per unit invested. Traditionally, sweet sorghum has served as a syrup crop and its culture and production are well understood. Sweet sorghum is genetically diverse and variations exits for characteristics such as Brix % (13–24), juice sucrose concentration (7.2–15.5%), total stalk sugar yield (as high as 12 Mg ha−1), fresh stalk yield (24–120 Mg ha−1), biomass yield (36–140 t ha−1) and others indicating potential for improvement. Transitioning sweet sorghum to a bioenergy crop is hampered by inadequate technology for large-scale harvest, transport and storage of the large quantities of biomass and juice produced, especially where the harvest window is short. Conversion of sweet sorghum to ethanol can be achieved by fermenting juice expressed from stems or directly fermenting chopped stalks. Integration of the fermentation and distillation of sweet sorghum juice in corn ethanol plants has not yet been achieved.