DETERMINATION OF MICROBIAL MINERALIZATION ACTIVITY IN SOIL BY MODIFIED WRIGHT AND HOBBIE METHOD

The Wright and Hobbie (1966) procedure, originally proposed for measurements of microbial activity in water, was adapted for soil studies. It was critically assessed, both for technical details and for the theoretical background of the isotope dilution principle. The heterogeneity of the soil microbial community was taken into account by introducing a double Michaelis-Menten equation instead of the simple Michaelis-Menten form. More complicated models were unsuitable because the kinetic parameters were not sufficiently stable in view of fluctuations of the experimental data within the measurement error. An integrated form of kinetic equation was preferable to a differential one, and a non-linear regression was better than a linear analysis of transformed data. In grey forest soil the heterotrophic potential of microorganisms was estimated to be 1.31 and 4.26 mg C h-1 kg-1 of soil for oligotrophic and copiotrophic components, respectively. The turnover time of indigenous, readily available, soil organic matter was 2.82 h.