Water Stress Effects on Ethanol Yield and Water Use Efficiency of Sweet Sorghum

With the increasing costs of fossil fuels both economically and environmentally, new methods of generating renewable fuels need to be researched and developed. This study was undertaken to assess the effects of water stress on the physiological characteristics and ethanol yield of Sweet Sorghum (Sorghum bicolor (L.) Moench). Three stress regimes (depletion of plant available water at 35, 50, and 65% volumetric soil water content) were established and applied before and after anthesis in a three by three factorial, allowing nine different treatments to be assessed. Soil type was a Gila very fine sandy loam (coarse-loamy, mixed, superactive, calcareous, thermic Typic Torrifluvent) and effluent irrigation water was applied by sub-surface drip irrigation with soil moisture being assessed by use of a Neutron Probe (CPN). Theoretical ethanol yield was calculated by multiplying total fermentable sugars determined from HPLC by 0.51 (conversion efficiency). For the pre-anthesis irrigation treatments, ethanol yield was highest at 50% depletion (3,189 L ha^-1), lowest at 65% depletion (2,535 L ha^-1), and intermediate at 35% depletion (2,862 L ha^-1). Ethanol yield was not affected by post-anthesis irrigations or by the interaction of pre- and post-anthesis irrigation treatments. Water use efficiency (water used divided by water applied) was highest in the post-anthesis 65% water depletion (85), intermediate at 50% depletion (81), and lowest at 35% (78). From this first season research it doesn't appear that post-anthesis water stress increases ethanol yield as found in other crops.