Soil Carbon and Macronutrient Changes Following Four Years of Bioenergy Sorghum Production.

Soil is the fundamental resource in agricultural systems and maintaining soil quality is key to sustainable production. Productivity and soil quality may be affected by cropping sequence complexity, fertilization, and residue removal. The goal of this research was to optimize crop management and soil quality in high biomass (bioenergy) sorghum [Sorghum bicolor (L.) Moench.] systems. The ongoing field study near College Station, Texas, utilizes a factorial treatment allocation within a randomized block design. There are four replications of the factors: Rotation: continuous bioenergy sorghum vs. biannual rotation with corn (Zea mays L.); 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 was a high-yielding photoperiod-sensitive hybrid. Other practices were those commonly used for production. Sorghum was harvested for yield and total concentrations of C, N, P and K. Soil samples were taken at the beginning of the study in 2008, with additional samples being collected before each subsequent growing season. Rotation, fertilization, and residue return affected several soil quality parameters (p < 0.05). Sorghum sequestered more soil organic carbon (OC) and total nitrogen (TN) to a depth of 90 centimeters. However, continuous sorghum production reduced Mehlich III extractable of soil P and K from 30 to 90 centimeters of depth compared to biannually rotated corn-sorghum systems. Near the soil surface, 50% biomass return had significantly higher OC, TN, and extractable P and K than 0 or 25% return.