Converting Bahiagrass Pasture Land to Elephantgrass Biomass Cropping Systems Alters Nutrients Dynamics.

Conversion of pasture lands to lignocellulosic bioenergy cropping systems will potentially stress native low fertility of coarse-textured soil in the southeastern U.S. Therefore, high biomass productivity can only be achieved through supplementary fertilizer application, which increases feedstock production cost and represents environmental risks due to offsite nutrient movement. The goal of this study was to assess nutrient management practices for elephantgrass [Pennisetum purpureum (L.) Schum.] compared with low-input bahiagrass (Paspalum notatum Flüggé). Treatments evaluated were 1) bahiagrass + 50 kg N ha-1 [BHG]; 2) elephantgrass + 50 kg N ha-1 [E50]; 3) elephantgrass + 50 kg N ha-1 + fermentation residual [E50FR]; 4) elephantgrass + 50 kg N ha-1 + biochar [E50BC]; and 5) elephantgrass + 250 kg N ha-1 [E250]. Soil macro and micronutrients levels, biomass mineral composition, and nutrient removal rates were determined. Although BHG exhibited at least two times higher N tissue concentration, elephantgrass soil N removal ranged from 4 to 16 times more regardless of treatment. Soil P and K levels were reduced by 57 and 49% in the E250 compared with BHG, respectively. Across years, soil Ca levels were 46% lower in both E50 and E250, whereas elephantgrass amended with bioenergy residuals maintained soil Ca levels throughout the study. Application of biochar in the E50BC increased soil levels of Mg, B, Zn, and Mn. Application of materials such as synthetic fertilizer or bioenergy residuals will be necessary to sustain long-term elephantgrass biomass productivity in the southeastern U.S. Bioenergy residuals could provide additional plant nutrients beyond NPK that do not appear to be toxic to elephantgrass and build up native fertility of marginal land.