Thiosulphate and tetrathionate oxidation in arable soils

Oxidation of thiosulphate (S2O32−) and tetrathionate (S4O62−), added at 300 mg S kg−1 soil, was studied in four arable soils at 25°C, over incubation periods of 0, 3, 7, 10, 20 and 30 d. Thiosulphate was oxidised rapidly to S4O62−, with most of the oxidation occurring within 3 d. In contrast, S4O62− was oxidised to SO42− much more slowly. Oxidation of S4O62− varied with soil type, being slower in a loamy soil (pH 5.8) than in three other soils (clay loam, silty clay loam and loamy sand, pH 6.2–7.0). An incubation experiment using autoclaved Rothamsted soil indicated a large abiotic component in the oxidation of S2O32− to S4O62−, whereas the oxidation of S4O62− to SO42− was of a biological nature. Production of SO42− was more rapid from the S2O32− amendment than from the S4O62− amendment, which suggested that either S2O32− primed the S4O62− oxidisers, or microorganisms were present that could oxidise S2O32− to SO42−, but not S4O62− to SO42−.