The level of soil moisture most favourable to the oxidation of elemental sulfur was found to be around the field moisture capacity; the oxidation rate decreased at lower and higher moisture levels. 2. The rate of oxidation increased with the clay content of the soils from sandy loam to clay loam. 3. Although S-oxidation could be found already at 10 degrees C, it increased markedly up to a maximum at 35 degrees C and then decreased again at higher temperatures. 4. Increasing the salt content of the soil (NaCl) reduced the rate of oxidation up to a concentration of 9 g salt/100 g soil; at a concentration of salt of 11 g/100 g soil no S-oxidation occurred. 5. Inoculation of the soil with Thiobacillus thiooxidans accelerated the S-oxidation, especially when organic matter was added. 6. In all experiments, S-oxidation was accompained by a decrease in pH.
