Tissue Chemistry of Potential Bioenergy Grasses.

Fertilization, nutrient removal and tissue composition of bioenergy crops will be major considerations in the economics, energetics, and environmental sustainability of candidate biofuel cropping systems. This study was conducted to determine the tissue chemistry of six potential biofuel grasses (elephantgrass, energycane, Erianthus, giant reed, Miscanthus, and sugarcane) across 3 sites in Florida. Sites in North and Central Florida on sandy soils received 280 kg N ha^-1 yr^-1 and 70 kg P₂O₅ ha^-1, whereas no N and 44 kg P₂O₅ ha^-1 were applied on muck soils at South Florida. Total N and P removal were significantly affected by species and were generally related to overall dry matter yields, but were only marginally affected by site (P = 0.07). Total N removal ranged from 32 kg ha^-1 for Miscanthus to 246 kg ha^-1 for elephantgrass. Similarly, total P removal ranged from 7 kg ha^-1 for Miscanthus to 43 kg ha^-1 for elephantgrass. Despite similar dry matter yields for elephantgrass and energycane, whole plant concentrations of N and P were 26% and 47% greater, respectively, in elephantgrass compared to energycane. The ratio of N to P in harvested biomass was also significantly different across species.  Neutral detergent fiber (NDF) and acid detergent fiber (ADF) analysis were affected by species and had site by species interactions.  Sugarcane had the lowest ADF, NDF and hemicellulose values while Miscanthus and Erianthus had the highest. Overall, high yields were associated with high nutrient removal rates; however we found that species selection has the potential to mitigate nutrient removal and contribute to improved economics, energetic and environmentally sustainability of intensive biofuel cropping systems based on tissue chemistry. Additionally, further studies on nutrient dynamics are needed to see whether reduced nutrient removal by energycane compared to elephantgrass, for example, represents poor uptake efficiency or increased internal cycling.