Evaluation of sweet sorghum planting density and minimal nitrogen input, under irrigated and non-irrigated conditions, for bioethanol feedstock production

Abstract

ABSTRACTSweet sorghum is a feedstock for bioethanol and is grown on a few hectares in the USA. Research was conducted to optimize the cultural management recommendations for sweet sorghum-based bioethanol production. Experiments were conducted using the ‘Top 76-6’ cultivar to evaluate the effect of nitrogen rate (84 and 168 kg N ha−1) and seeding rate (114, 143, 191, 286 and 571 kg ha−1) or population density (41,000, 51,100, 68,200, 10,2500 and 205,000 plants ha−1) on biomass and sugar yield with or without irrigation. In 2012, we evaluated seeding rate and nitrogen effects. With irrigation, the lowest seeding rate produced the most biomass (44,588 kg ha−1), equivalent to 3.25 Mg ha−1 sugar. Biomoass increased with more nitrogen across seeding rates. Without irrigation, neither seeding rate nor N rate impacted biomass or sugar yield. In 2013 and 2015, biomass ranged from 49,000 to 92,000 kg ha−1 with irrigation and 45,000 to 54,000 kg ha−1 without irrigation. The greatest biomass (∼49,000 to 54,000 kg ha−1) was obtained at the two highest population densities. Applying more N had no effect on biomass regardless of population density, except in 2013 without irrigation. With irrigation, optimum productivity can be achieved at low population density with minimum nitrogen input.