Factors affecting oxidation rates of elemental sulphur in a soil under a ryegrass dominant sward

Abstract

Field and laboratory experiments were used to determine the effects of two consecutive applications of elemental sulphur (S°) on the S° oxidation rates and numbers of thiobacilli in a soil under a ryegrass dominant sward. The S° in soil samples were extracted into chloroform and analysed by a high performance liquid chromatography procedure. The rate of S° oxidation in the field experiment, expressed as the time in days required to oxidise 70% of added S°, decreased with decreasing diameter of S° particles because of the larger surface area of fine S° particles available for oxidation. Oxidation rates of S° also increased when S° was reapplied in autumn and spring because of the presence of large numbers of thiobacilli remaining from the first S° application and the higher soil temperatures and moisture conditions. These field observations were confirmed in laboratory experiments. Scanning electron microscopy of the S° particles showed that most were irregularly shaped with uneven, perforated surfaces. Spherical particles occurred infrequently and had smooth surfaces.