Harvest Method Effect On Sugar Composition of Sweet Sorghum.

Sweet Sorghum(Sorghum bicolor L. Moench.) is being evaluated as a biomass energy crop for conversion of its sugar  to ethanol. Maintaining the quantity and quality of sugars post harvest is important. Extraction and sugar composition over a 48+ h period was examined in south Florida in 2009 using two cultivars(‘Dale’ & ‘M81E’) harvested as whole plants, chopped into 25 cm long billets and chopped similar to corn silage into 1cm pieces at three harvest times. Percent juice extraction remained relatively constant over the 48 h period. Percent Brix remained relatively constant over the 48 h period for whole plant and billets but declined rapidly after 15-25 h with silage. HPLC profiles of individual sugars revealed that percent sucrose decreased rapidly after just a few hours post harvest with all three harvest methods. These results suggest that if silage harvesters are used to harvest sweet sorghum for ultimate sugar conversion to ethanol, biomass will need to be processed within about 15 hours or chemical or other treatments may be needed to reduce total sugar loss. The rapid conversion of sucrose may also require processing adjustments regardless of harvest method. This study suggests that genetic improvement in sugar physiology and metabolism could make sweet sorghum a even better crop for conversion to ethanol.