Partitioning of the Effects of Plant Trash on Sweet Sorghum Biomass Yield, Fiber Content and Juice Quality Parameters

The objectives of this research were to measure the amounts of biomass and sugar yields and proportionality of sugars in juice of sweet sorghum (Sorghum bicolor (L.) Moench) harvested and processed with different sources of vegetative material, i.e., stalks with panicles and leaves intact; stalks with only leaves intact; stalks with only panicles intact; and stalks with leaves and panicles removed. Early- and medium-maturity hybrids planted at the optimum time provided plant material for sampling at the hard-dough stage of seed maturation. Data were recorded for juice brix and purity, sugars in juice, fiber, ash and weight of juice, biomass and total fermentable sugar. Increasing levels of trashy material generally resulted in higher fiber, but lower brix and purity. Clean samples and samples with just panicles produced lower fresh and dry weight and juice yield compared to the trashier samples. Fermentable sugar yield did not vary among treatments. While treatment differences for fermentable sugar yield in Mg ha(-1) were not significant, comparisons made on a g of sugars in juice g drywt(-1) basis produced sizeable reductions in total fermentable sugar. Samples of stalks with both panicles and leaves intact contained 25.6% less total fermentable sugar than stripped stalks. Sucrose was the dominant sugar for both clean and trashy stalks. Levels of glucose and fructose were considerably lower than that of sucrose. In general, the order in which trash adversely affected juice quality parameters was stalks with leaves and panicles > stalks with leaves > stalks with panicles > stripped stalks.