Differential extraction of radiocarbon associated with soil biomass and humus

To detect the humification of organic compounds in soil that bypasses bioma ss incorporation, selective extraction procedures for radiocarbon from soil biomass and humus were! evaluated. Following the incubation of C-14-glucos e and C-14-benzoate in soil, fumigation-0.5 M K2SO4 extraction and 0.15 M N a4P2O7 extraction selectively removed biomass-associated and humus-associat ed radiocarbon, respectively. Applying the recovery correction of 3.4X to b iomass and 3.5X to humus, radiocarbon balances of 95 to 107% were obtained during a time window following the degradation of these substrates. Negligi ble overlap between the extractions renders the technique suitable for inve stigating the fate of organics that, through cometabolism, attain unusual r adiocarbon distributions in soil.