Can Biochar and Fermentation Residual Enhance Biomass and Soil Carbon in Elephantgrass Grown for Bioenergy.

Conventional food, feed, and fiber agricultural landscapes are already being converted to biofuel cropping systems, and this is expected to intensify as demand for bioenergy grows. However, the implications of this conversion for agroecosystem services are not well understood. The objectives of this project were to quantify and compare the effects on shoot production, root production, and soil carbon between a bahiagrass (Paspalum notatum) pasture system (T1) and elephantgrass (Pennisetum purpureum) biofuel cropping systems with different C and N inputs, including 50 kg fertilizer N ha^-1 alone (T2), with evaporated fermentation residual (T3), with biochar (T4), and 250 kg fertilizer N ha^-1 alone (T5), all established in fall 2012 at Citra, Florida. During the first growing season (2013) following establishment, dry shoot biomass yield was greater for elephantgrass compared to bahiagrass, but the elephantgrass yields were similar (> 40 Mg ha^-1) across all treatments. Elephantgrass shoot yields were also similar across treatments for the second growing season (about 25 Mg ha^-1), but lower than year one.  After establishment, bahiagrass root production was similar to elephantgrass in the upper soil profile (0-20 cm) and greater in the lower soil profile (20-40 cm). Increased root production in the upper soil was seen for T3 compared to the other elephantgrass treatments, which were similar. After two growing seasons, bahiagrass and elephantgrass amended with biochar had the greatest enhancement in soil C with increases at all measured soil depths compared to initial conditions. Elephantgrass with evaporated fermentation residual (10-40 cm) and T5 (0-40 cm) negatively affected soil C in the upper soil. Compared to bahiagrass, high shoot yields of elephantgrass for bioenergy conversion are possible, but with potentially adverse consequences for soil C accumulation, which could be offset by biochar amendment, but not with addition of the evaporated fermentation residual.