Sugar Yield of Sweet Pearl Millet and Sweet Sorghum as Influenced by Harvest Dates and Delays Between Biomass Chopping and Pressing

Sweet pearl millet [Pennisetum glaucum (L.) R.Br] and sweet sorghum [Sorghum bicolor (L.) Moench] have been identified as possible ethanol feedstocks because of their high biomass yield and concentration of readily fermentable sugars, but the effects of harvest dates and delays between biomass harvest and pressing on sugar yield and concentration are poorly known. The objective of this study was to determine the effects of two species, two harvest dates (August and September), and four delays between chopping and pressing (0.5, 2, 4, and 6 h) on yields and concentrations of nonstructural carbohydrates [NSC = water-soluble carbohydrates (WSC) + starch] of the biomass, bagasse, and extracted juice. An experiment was conducted at two contrasted sites in Qu,bec, Canada [Saint-Augustin-de-Desmaures, 2,300-2,500 corn heat units (CHU); and Sainte-Anne-de-Bellevue, 2,900-3,100 CHU], in 2010. Sweet sorghum had lower biomass yield (15.8 vs. 20.4 Mg dry matter (DM) ha(-1)), but greater biomass NSC concentration (242 vs. 128 g kg(-1) DM), extracted juice NSC concentration (61 vs. 42 g L-1) and yield (2.8 vs. 2.2 Mg ha(-1)) than sweet pearl millet. Delaying harvest increased biomass yield (+7 Mg DM ha(-1)), NSC concentrations of biomass (+97 g kg(-1) DM), bagasse (+70 g kg(-1) DM), and extracted juice (+38 g L-1), and NSC yield from the extracted juice (+1.6 Mg ha(-1)). The maximum extracted juice NSC yield (3.9 Mg ha(-1)) was obtained with sweet sorghum harvested in September. Delaying pressing the biomass up to 6 h after chopping did not affect NSC concentration and yield of the extracted juice.