EVALUATION OF METHODS TO ESTIMATE THE SOIL MICROBIAL BIOMASS AND THE RELATIONSHIP WITH SOIL TEXTURE AND ORGANIC-MATTER

Three methods to estimate soil microbial biomass, CHCl3 fumigation-incubation (CFI), CHCl3 fumigation-extraction (CFE), and substrate-induced respiration (SIR), were compared with each other and with arginine ammonification and basal respiration using soils over a wide range of textural classes and organic matter content. Biomass and activity of the soil microflora were significantly related to clay, soil organic C and especially to total N content. Values for microbial biomass C as estimated by CFI, CFE and SIR were highly correlated and not affected by soil texture. Only the estimation of biomass C by CFE was slightly influenced by soil organic matter including the two peat soils into the regression analysis. While the absolute values for biomass C deviated considerably when estimated by CFI, CFE and SIR, the ranking of the soils was the same for all these methods. These differences were usually not caused by the abiotic soil conditions we examined. The factors to convert the additional amount of organic C extracted after CHCl3 fumigation or the substrate-induced respiration to microbial biomass C are discussed.