Management, Productivity and Nutrient Relationships in Biomass Sorghum Systems.

Bioenergy sorghum (Sorghum bicolor L. Moench.) productivity and nutrient uptake may be affected by management practices. The goal of this research was to optimize the efficiency and sustainability of high biomass (bioenergy) sorghum production systems. Results are reported for the last three years (2010, 2011, and 2012) of a four-year field study conducted near College Station, Texas. The study utilized a complete factorial design with four replications of the following factors: Rotation: continuous biomass sorghum vs. biannual rotation with corn (Zea mays L.); Stover Return: 0, 25, or 50% of the sorghum biomass and all corn stover; and N Rate: 0 vs. non-limiting N. The bioenergy sorghum used was a high-yielding photoperiod-sensitive hybrid. Sorghum was harvested for yield, and C, N, P K, Ca, Mg, Mn, Zn, Fe, and Cu concentrations and contents were determined. All three study factors affected plant growth, yield, and nutrient uptake (p < 0.05). Total yields and tissue concentrations of C, N, P, Ca, Mg, Mn, Zn, Fe, and Cu in sorghum biomass were significantly (p < 0.05) affected by rotation and N fertilization. Rotation and N fertilization increased sorghum yield, but variably affected elemental composition. Not returning any sorghum residue in previous years decreased continuous sorghum yield in 2011 and 2012. Highest yields in 2012 were seen under the 25% return rate (p < 0.05). A regression equation was developed relating sorghum biomass yield and rotation, nitrogen fertilization rate, and soil total N and extractable P in the surface 15 cm (R² = 0.75).