Measurement of microbial sulfur in soil

A technique was developed to estimate the amount of sulfur held by the microbial population in soil. This method involves lysing the microbial cells with chloroform and measuring the S released to 10 mm CaCl₂ or 0.1 m NaHCO₃ extracts. Calculations of biomass-S were made from the experimentally determined proportion of cell S released. To determine this proportion, two species each of bacteria and fungi, which were grown at three concentrations of S, were added to the soil and treated with CHCl₃. The average values of 34.6% with CaCl₂ and 41.2% with NaHCO₃ were calculated for the proportion of microbial S extracted following CHCl₃ treatment. Biomass-S was found to represent approximately 2.3% of the total S in the soil.