THIOSULFATE AND TETRATHIONATE OXIDATION IN ARABLE SOILS

Oxidation of thiosulphate (S2O32-) and tetrathionate (S4O62-), added a t 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 w ithin 3d. In contrast, S4O62- was oxidised to SO42- much more slowly. Oxidation of S4O62- varied with soil type, being slower in a loamy soi l (pH 5.8) than in three other soils (clay loam, silty clay loam and l oamy sand, pH 6.2-7.0). An incubation experiment using autoclaved Roth amsted soil indicated a large abiotic component in the oxidation of S2 O32- to S4O62-, whereas the oxidation of S4O62- to SO42- was of a biol ogical nature. Production of SO42- was more rapid from the S2O32- amen dment than from the S4O62- amendment, which suggested that either S2O3 2- primed the SO42- oxidisers, or microorganisms were present that cou ld oxidise S2O32- to SO42-, but not S4O62- to SO42-. (C) 1998 Publishe d by Elsevier Science Ltd. All rights reserved.