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 degrees 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 3d. 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 SO42- oxidisers, or microorganisms were present that could oxidise S2O32- to SO42-, but not S4O62- to SO42-. (C) 1998 Published by Elsevier Science Ltd. All rights reserved.