Agronomic Practices for Production of Ethanol from Sweet Sorghum

Abstract

Sweet sorghum [Sorghum bicolor (L.) Moench] is a potential alternative feedstock for ethanol production, but its viability will depend upon knowledge of cultural practices which optimize energy yield. Several field studies were conducted in 1987 and 1988 to evaluate the influence of planting date, harvest date, N fertilizers, and plant density on performance of sweet sorghum for ethanol production in the northern Corn Belt. Four sweet sorghum cultivars were planted in late April, early May, mid-May, and late May of 1987 and 1988 at Waseca, MN. Percent fermentable carbohydrate (°Brix or °B) and stalk moisture content were measured at two week intervals from August through October and stalk dry matter and ethanol yields were determined at harvest In mid-October. Dry matter yields ranged from 8 to 10 tons/acre and ethanol yields from 326 to 423 gal/acre with the best cultivar, ‘Keller’. Dry matter yield decreased as planting date was delayed, but °B and stalk moisture were only slightly affected by delayed planting. Fermentable carbohydrate and ethanol yields were about 13% higher at earlier planting dates than at later planting dates. Keller, a late-maturing cultivar, had greater °B and ethanol yields than three other cultivars, but was nearly 100% lodged at harvest. Maximum stalk °B was produced mid- to late September. Neither N fertilizers nor seeding rate significantly affected fermentable carbohydrate or ethanol yield. Early planting dates and late-maturing cultivars with high °B levels are recommended for sweet sorghum, when grown for ethanol in the upper Midwest.