Oxidation of Elemental Sulfur in Soils

Abstract

Studies of oxidation of elemental S in soils showed that thiosulfate and tetrathionate are produced during S oxidation in soils. In this work, unamended and elemental S‐amended soils were incubated (30°C) under aerobic conditions for various times. The amounts of S₂O_3‐, S₄O_6‐, and SO_4‐S produced during incubation were determined. Results showed that S₂O₃^2‐ was produced within the first few days of incubation and that S₄O₆^2‐ accumulated in some soils. The rate of S oxidation increased with increasing incubation temperature (5, 15, and 30°C) and with increasing the rate of S application (50, 100, and 200 µg S/g soil). For 100 µg S/g soil, the rates of oxidation of elemental S in 10 Iowa surface soils ranged from 39 to 75 µg S/g soil after incubation at 30°C for 70 days; rates were more rapid in alkaline soils than in acid soils. There was little change in pH of soils even when the S application rate was increased from 50 to 200 µg S/g soil. The rate of S oxidation was lower in air‐dried soils than in field‐moist soils.