Utilization of Annual Warm-Season Grasses As Biofuel Source and Feedstock by-Product.

Annual warm-season grasses such as forage sorghum, sorghum x sudangrass hybrid and sundangrass are highly productive and valuable feed crops (rotational crop and silage).  Many of these crops could also be used as possible biofuel crops.  Sugar in the stems of these warm-season grasses can be extracted and fermented, while the cellulose in the bagasse (pressed stalk) can be used for feedstock or cellulosic ethanol, making these very versatile crops.  The objective of the study was to determine the use of warm-season grasses in a dual biomass production system.  The experimental design was a randomized complete block, replicated four times.  The study included 12 annual warm-season grasses which included forage sorghums, sudangrass, sorghum x sundangrass hybrid and pearl millet.  All plots were planted at seeding rate of 28 kg ha^-1 in a 1.82 m x 3.35 m plot.  Plots were harvested when 50% of the plots were in the boot stage.  Plots were fertilized with 56 kg N ha^-1 using urea ammonium sulfate.  Prior to harvest, plant population measurements were taken using two 1m² quadrats placed sequentially in the middle of each plot.  Eight stalks were randomly cut at a height of 7.5 cm from the ground for sap extraction; fresh weight (including leaves and stems) was recorded.  Sap was extracted from whole plant using a sugar cane press and sap weight, volume and °Brix were recorded.  A 50 mL sample of sap was frozen for further sugar analysis using HPLC at the Mississippi State University Chemical Laboratory.   Half of the bagasse was processed for silage and half was oven dried at 66 °C and analyzed for nutritive value.  Plots were harvested (chopped) for total yield and a subsample was collected for dry matter determination and ensiling.  Data was analyzed using the SAS program Proc GLM.  Piper sudangrass had lower dry matter yield and sap production.  There was no significant difference in °Brix among the different varieties.  Dry matter yields were lower than expected, affected by late planting and droughty conditions.