Sweet sorghum is being investigated as a feedstock for ethanol production in semi-arid countries. It can be grown with fewer inputs than other energy crops. In Iran, due to long growing season, ethanol is produced from both sweet sorghum stem and grain. In other countries, ethanol is not produced from sweet sorghum grain due to low grain yield or short growing season. The purpose of this study was to maximize ethanol production from both stem and grain of sweet sorghum. Four planting dates (July 5, July 14, July 25 and August 4) and three nitrogen levels (50, 100 and 150 kg/ha urea) were assigned to the main and subplots, respectively. Plants were harvested at physiological maturity. Stem measurements were: stalk height, stalk diameter, stalk fresh yield, brix value, sucrose content, total sugar and ethanol yield and grain measurements were: number of grain per panicle, 1000 grain weight, grain yield, biological yield, harvest index and ethanol yield. Stem measurements were highest in July 5 planting and lowest in August 4 planting, while grain measurements were highest and lowest in August 4 and July 5 plantings, respectively. Stem and grain measurements in July 15 and July 25 were intermediate. More grain yield, 1000 grain weight and number of grain/panicle were obtained with the application of 150 kg/ha urea than the other two nitrogen levels. Based on the results, in order to obtain the highest ethanol yield from both stem and grain, it is suggested to plant sweet sorghum as early as possible and apply 150 kg/ha urea.
Key words: Sweet sorghum, temperature, planting date, ethanol production, nitrogen levels.
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