Amending marginal sandy soils with biochar and lignocellulosic fermentation residual sustains fertility in elephantgrass bioenergy cropping systems
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Perennial grasses offer potential for high lignocellulosic biomass yields on marginal land that can be used for conversion to biofuels. However, fertilizer nutrient inputs are often required to maintain high yields. This study evaluated biochar and fermentation residuals as alternative supplemental nutrient sources for elephantgrass (Pennisetum purpureum (L.) Schum.) feedstock production. Treatments were (1) 50 kg N ha−1 (E50); (2) 50 kg N ha−1 + fermentation residual (E50FR); (3) 50 kg N ha−1 + biochar (E50BC); and (4) 250 kg N ha−1 (E250). The E50 treatment was not enough to sustain elephantgrass yields over time, as E250 biomass yields were greater in years 3 and 4 compared with E50. Residual amendments had little effect on yield. Plant N concentration in E250 (7.5 g kg−1) was twofold greater compared with all other treatments along with generally greater N removal. Residuals were largely unable to supply additional N, as they did not increase tissue N concentrations or N removal compared with E50. Across years, soil P and Ca levels were 59 and 46% lower, respectively, for E50 and E250 than for E50FR and E50BC, which maintained nearly constant levels throughout the study. Application of biochar (E50BC) increased soil concentrations of Mg, B, Zn, and Mn. Supplemental nutrients are needed to sustain long-term elephantgrass productivity on marginal land of the southeastern U.S. Bioenergy residuals may fill this role when combined with low fertilizer N and possibly K inputs. Identifying optimal amendment application rates will be important to prevent excess accumulation of some elements.
KeywordsSoil fertility Nutrient management Bioenergy Elephantgrass Residuals Biochar Nutrient cycling
Funding for this research was supported by the National Institute of Food and Agriculture, U.S. Department of Agriculture through competitive Grant Number 2012-67009-19596. We would also like to acknowledge Jeffrey Fedenko, Rezzy Manning, Danilo Quadros, and Andrew Schreffler for their assistance in the field and/or lab.
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