Effect of Agronomic Management Practices On Soil Microbial Biomass Carbon and Nitrogen Under Bioenergy Sorghum Production.

Growing demands for domestic biofuel production have launched aggressive efforts to investigate suitable crops for fuel production. Bioenergy sorghum is one source of biomass feedstock which is being examined in Texas and throughout the southern U.S. Soil and crop management practices associated with production of bioenergy sorghum can influence soil biological activity and overall soil health. Soil microbial biomass (SMB) carbon (C) and nitrogen (N) are labile components of soil organic matter which are critical to nutrient cycling and valuable indicators of overall soil health. The aim of this study was to understand the effects of crop rotation, N fertilization, and residue return rate on SMB C and N pools in a bioenergy sorghum cropping system in central Texas. Soil samples were collected after crop harvest, in November 2011, at two depths for analysis. The chloroform fumigation-extraction method was utilized for removal of SMB C and N followed by combustion analysis. Preliminary results indicated residue return increased SMB C and N compared to not returning residue. Microbial populations may have been able to proliferate to higher concentrations where residue was added because of  more organic C in these treatments. Results also suggested that residue return promoted greater nutrient cycling and overall soil health. Further investigation is needed to determine effects of different agronomic practices and to quantify the magnitude of difference between practices.