ATTEMPTS TO DETERMINE AVAILABLE CARBON IN SOILS

The size of the C pool that is readily available to microorganisms affects important N transformations that occur in soils, e.g., denitrification and N immobilization. In the present work, the C content of soil extracts, the C in water displaced from soil and biomass C were compared as indicators of available C. A comparison of C measured by the anthrone method and a total organic-C analysis of extracts indicated that only a small portion of C was in carbohydrates. The substrate-induced respiration method of measuring biomass in conjunction with the Wright-Hobbie model was used as an additional determination of available C. Total organic-C analysis of a 1 N H2SO4 extract gave the highest C values (500-1700 mg C kg-1 soil) and the substrate-induced respiration method gave the lowest (1-5 mg glucose equivalents kg-1 soil). The C values closest to the C turnover measured in long-term incubation studies were obtained by the substrate-induced respiration method using the Wright-Hobbie model. © 1990 Springer-Verlag.