AbstractWater‐soluble sulphate and total sulphide levels were determined during 0, 3, 6 and 12 weeks' incubation (30°) of soil at varying moisture contents (0–133% mwhc) with and without addition of 1 % organic materials (cellulose, compost and dwarf peas, all in a finely ground state). With added peas, conditions were apparently anaerobic at all moisture contents, since immobilisation of sulphate and accumulation of sulphide occurred. Where cellulose or compost were added, sulphide accumulated only at 80% mwhc and higher moisture contents, and increased with moisture content. In unamended soil and soil + compost only sulphate accumulated at 20–60 % mwhc and accumulation increased with moisture content in this range. Where cellulose was added sulphate immobilisation occurred and was less at 20–60% mwhc than at higher moisture levels. At 80% mwhc or more anaerobic effects were predominent. The optimum moisture contents for the accumulation of sulphate and sulphide were 60% and 133% mwhc respectively.