Rhodanese converts S2O32− to SO32−, both of which are intermediates during the oxidation of elemental sulfur (S°). AI though rhodanese activity has been detected in soils, its role in S° oxidation is not well understood. This study investigated the effects of time, temperature, and water potential on rhodanese activity in S° amended soils. Air drying decreased or increased S° oxidation depending on soil type, whereas air drying decreased rhodanese activity in all four soils tested. The relationship of S° oxidation to rhodanese activity was not consistent among all soil types. The Woodburn soil (Aqultic Argix-eroll) had high S° oxidation potential but low rhodanese activity, whereas the Amity soil (Argiaquic Xeric Argialboll) had high rhodanese activity but low S° oxidation. The rate of S° oxidation reached a maximum after 7 or 14 days depending on soil type, but rhodanese activity decreased with time up to 28 days in all soils. In three of the four soils tested the addition of K2SO4 or Na4SO4 (450 mg SO42− – S kg−1 soil) suppressed rhodanese activity after 28 days incubation at 23°C, indicating that the end product of S° oxidation (SO42−) has a potential role in suppressing rhodanese activity. We conducted an experiment including a complete factorial of five temperatures (10, 20, 25, 30, and 40°C) and five water potentials (ranging from approximately −0.005 to −10 megapascal (MPa) to determine the influence of these parameters on S° oxidation and rhodanese activity in five soils. Optimum temperature for S° oxidation ranged from 25 to 30°C, and optimum water potential was −0.02 MPa in three silty clay or silt loam soils, −0.01 MPa in a sandy loam soil, and −0.1 MPa in a sandy soil (Quincy). Unlike the other four soils, the course-textured soil (Quincy), high in sand content (>89% sand), exhibited increased rhodanese activity with increasing water potential at temperatures ranging from 10 to 30°C, but at 40°C rhodanese activity decreased with increasing water potential. We found no direct relationship between S° oxidation and rhodanese activity in this study. © 1990 Williams and Wilkins.
