Effect of agronomics on production and conversion quality of Napiergrass

Napiergrass (Pennisetum purpureum (L) Schum) is being developed as a bioenergy crop for production in the southeastern United States.  An important criterion for selecting a crop is establishing a consistent and dependable source of feedstock.  In this study, we considered the effects of fertilizer application and cutting regimes on production yield, chemical composition and theoretical ethanol yields, and enzymatic sugar conversion efficiencies.  The sample set consisted of two year established plots (Shellman, GA) with three treatments, where were selected to maximize production yields, and replicated 4-fold.  Production yields were 29.2 – 38.7 Mg/ha of dry matter.  Samples were analyzed for soluble sugars, starch, structural carbohydrates, uronic acids, and Klason lignin.  Glucan and total structural carbohydrate contents were 303 - 362 and 516 -610 g/kg, db, respectively.  Acid Insoluble lignin contents were 123 – 182 g/kg, db.  Low-moisture ammonium hydroxide (LMLA) was selected as the pretreatment strategy to prepare the biomass for enzymatic conversion.  Pretreatment conditions were optimized for enzymatic sugar conversion using a central composite design and a single selected sample; these were: 20% g ammonium per g biomass, 110°C for 2 days.  The enzyme formulation consisted of commercial celluases (5 FPU/g), xylanases (130 IU/g), and pectinase (15 IU xylanase/g).  Glucose and xylose enzymatic conversion efficiencies were 91 – 109% glucose (only accounting for cellulose) and 67-77% xylose. In summary, conversion efficiencies were observed to vary enough to warrant their consideration when formulating biomass production strategies.