Production of Napiergrass (Pennisetum purpureum Schum) for Bioenergy Under Organic Versus Inorganic Fertilization In the Southeast USA.

Napiergrass (Pennisetum purpureum Schum.) is being considered for use as a feedstock for the emerging bioenergy industry in the Southeast USA.  Poultry litter is a readily available source of nutrients that could be used as a low cost fertilizer for biomass crops.  The purpose of this study was to compare biomass production and nutrient uptake of napiergrass fertilized with poultry litter, inorganic fertilizer, or unfertilized control.  Napiergrass cultivar Merkeron was planted in fall 2006 near Tifton, GA on gently sloping plots.  Metal dividers were placed between plots, and automated collection units were placed at the bottom of each plot to measure surface runoff.  Beginning in spring 2007 approximately 84 kg N/ha was applied as poultry litter or equivalent inorganic fertilizer yearly.  Inorganic P and K were also applied in amounts equivalent to the poultry litter (approximately 1:1:1 ratio).  Biomass was harvested each winter after senescence.  Biomass yields of the two fertilized treatments were not significantly different.  In the third and fourth seasons the unfertilized control plots yielded less than the fertilized treatments.   In only the first two harvests biomass N concentration was greater in the inorganic treatment than in the control.  Biomass C/N ratios of the control and poultry litter treatments were not different in any harvests, while the inorganic treatment had lower C/N ratio in the second and third harvests.  Soil cores were taken from each plot yearly to assess possible affects of fertilizer treatments on the soil.  No significant changes in soil C and N pools were observed, though a lower soil pH was measured in the 0–15 cm layer of the inorganically fertilized plots.  From 24 runoff events, the mean concentrations of NH₄ and NO₃ were greatest in runoff from the plots receiving poultry litter and least from the control plots.  The mean concentrations of PO₄ and Cl were greatest in runoff from the plots receiving inorganic fertilizer and least from the control plots.  Poultry litter can be used as a fertilizer for biomass crops in the Southeast.