OXIDATION OF ELEMENTAL SULFUR UNDER FIELD CONDITIONS IN CENTRAL SASKATCHEWAN

Abstract

A field study was conducted at 4 sites in central Saskatchewan to examine the oxidation rate of elemental S and its influence on soil pH. Finely divided S (approximately 7-μm diameter) was applied at a rate of 200 kg ha−1 to soil cores in aluminum cylinders. Three entire cores from each site were removed and analyzed for sulfate content and soil pH four times during a 16-mo period. All four soils exhibited significant oxidative activity. Twenty-three to forty-five percent of applied S was recovered as sulfate 10 wk after application. Sulfate concentrations recovered in the soil profiles declined after approximately 1 yr, partly due to leaching losses. Fertilizer-derived sulfate was most persistent in soils of finer texture. In the coarse-textured soils, most of the fertilizer-derived sulfate was apparently leached from the soil profile by the end of the 16-mo period. Soil pH was marginally reduced by oxidation following the application of elemental S but differences were no longer statistically significant at the last sampling time. Field incubation with elemental S substantially enhanced subsequent oxidative activity in three of the soils, suggesting that an initial application of elemental S fertilizer would enhance the effectiveness of subsequent applications. Substantial oxidation activity occurs in Saskatchewan soils even under the less than ideal conditions prevalent in this climatic region. It was concluded that elemental S in a finely divided form has strong potential as an effective fertilizer S source if appropriate fertilization strategies are adopted to maximize oxidation rate or compensate for delays in plant-available S release. Key words: Elemental S, pH, leaching, sulfate, immobilization