Varietal Differences and the Impact of Drought Stress On Bioenergy Traits of Forage and Sweet Sorghum.

Biofuels are positioned to play an important role in our sustainable energy future, but the impacts they have on water and land resources must be carefully evaluated.  Sorghum is considered a multi-purpose energy crop, and although it is drought and heat tolerant compared with other crops, little research has evaluated the impacts of drought stress on sorghum production and bioenergy traits. Using 17 varieties, we measured traits contributing to qualitative and quantitative biomass accumulation in dryland and irrigated conditions at three sites. We assessed growth, biomass, cell-wall composition, sap brix and physiological traits. Additionally, because sorghum can be used for forage, we assessed nutritional value with in-vitro neutral detergent fiber which correlates to dry matter intake, ruminal fermentation, and milk production in early lactation dairy cows. The 2012 season was hot and dry: two sites (Akron and Walsh) had 66 and 71 days, respectively, over 32 °C and extreme conditions (drought, heat, wind, weed pressure) and limited irrigation capabilities resulted in poor and variable yields at these locations. The third site (Fort Collins) had fewer hot days and higher irrigation availability which resulted in higher overall yields. Yield and brix were both strongly influenced by water treatment: brix was higher in dryland treatments, but total juice volumes were greatly reduced.  Total yields were strongly correlated to Stem Harvest Indexes.  Total biomass yields in the field were positively correlated with photosynthesis and stomatal conductance in the greenhouse, but negatively correlated to instantaneous water use efficiency (WUE).