A COMPARISON OF METHODS FOR ESTIMATING SOIL MICROBIAL BIOMASS CARBON

Soil microbial biomass is an important ecological parameter because it acts as a source-sink in nutrient cycling processes and regulates many organic matter transformations. Appropriate methodologies must be developed to measure the microbial pools in natural and man-managed (agroeco-systems) systems. Our objective was to compare and contrast the conventional chloroform fumigation incubation method (CFIM) with the chloroform direct extraction method (CFEM) using automated analyses of total organic carbon for determining microbial biomass carbon. Fresh soil samples were taken at 0-5- and 5-15-cm depths from two sites with different clay contents in the Georgia Piedmont and analyzed by both methods simultaneously. Both methods gave the same general trends of reduced microbial carbon with depth even when using different k(c) or k(ec) values. At 0-5 cm, each method gave different results for the high-clay (HC) sites. This further emphasizes the need to independently determine k(c) or k(ec) values for characteristically high clay soil in the Piedmont. The variability between replicates for CFIM was greater than CFEM. These preliminary results suggest that the CFEM using the total organic carbon (TOC) analyzer may be more appropriate for evaluating soil microbial biomass carbon, especially where a large number of samples are processed.