A Comparison of Sweet Sorghum Cultivars and Maize for Ethanol Production

Abstract

Sweet sorghum [Sorghum bicolor (L.) Moench] is a potential feedstock for ethanol production in many regions of the world. The objective of this study was to compare sweet sorghum cultivars with maize (Zea mays L.) as alternatives for ethanol production in the northern Corn Belt. Thirteen sweet sorghum cultivars were compared with an adapted maize hybrid grown on clay loam soils (Aquic or Typic Ha-pludols) in a randomized complete block design in 1987 and 1988. The fermentable carbohydrate content, or Brix (°B), of sorghum stalk sap was measured with a refractometer, and ethanol yields were calculated assuming 14.7 pounds fermentable carbohydrate per gallon ethanol. Ethanol yield from maize was calculated from the harvested grain assuming 22.4 lb maize grain per gallon of ethanol. Sorghum cultivars varied significantly in dry matter production, °B, fermentable carbohydrate yield, and ethanol yield. The best sorghum cultivars (Keller, Dale, and Smith) produced more ethanol than maize in 1988, a dry year, and were similar to maize in 1987, a more normal year. Averaged over both years, public cultivars Keller, Dale, and Smith were superior to most other sorghum cultivars or hybrids. Lodging was most severe for the sweet sorghum cultivars with the highest fermentable carbohydrate yields. Sweet sorghum appears to be a viable alternative source of ethanol compared with maize for the northern Midwest, but high fermentable carbohydrate, lodging resistant cultivars are needed.