Bioenergy Sorghum Management Affects Yield, Nutrient Uptake and Soil Quality.

Management strategies including rotation, fertilization and residue return may help optimize sustainable biomass sorghum production systems. The goals of this research were to optimize crop management and soil and environmental quality in high biomass (bioenergy) sorghum systems. The ongoing field study near College Station, TX utilizes a factorial design with four replications of the following factors: Rotation: continuous biomass sorghum vs. biannual rotation with corn; Biomass Return: 0, 25, 50% of the sorghum biomass and all corn stover; and N Rate: 0 vs. non-limiting N. The bioenergy sorghum used in all studies was a high-yielding photoperiod-sensitive hybrid.  All other inputs and practices were those commonly used. Sorghum was harvested for yield, with concentrations of C, N, P, K, and other nutrients being determined.  Soil samples were taken with depth at the beginning of the study, with additional samples collected before subsequent growing seasons. Soil samples were analyzed for quality parameters including total soil organic C (SOC) and nitrogen (TN), residual nitrate (NO₃^-) and other available nutrients. Rotation was the dominant factor, significantly influencing (p < 0.05) sorghum yield, content of C, N, P and K, and extractable soil NO₃^-, P, and K and SOC and TN. Nitrogen fertilization also increased (p < 0.05) yield, sorghum tissue N concentration, and soil NO₃^-. Residue return significantly (p < 0.05) impacted sorghum yield, with mean yields increased by biomass return. Biomass return also significantly increased (p < 0.05) SOC, TN, and extractable soil P and K, while decreasing soil NO₃^- to a depth of at least 15 cm. A regression equation was developed relating biomass yield to rotation, nitrogen fertilization rate, and soil total N and extractable P in the surface 15 cm (R² = 0.75).