IMPACT OF ELEMENTAL SULFUR FERTILIZATION ON AGRICULTURAL SOILS. II. EFFECTS ON SULFUR-OXIDIZING POPULATIONS AND OXIDATION RATES

Abstract

Effects of elemental sulfur fertilization on sulfur-oxidizing populations, rhodanese activity, total sulfur content and sulfur oxidation rates in the 0- to 15-cm zone of two Grey Luvisolic soils were assessed. Heterotrophic sulfur oxidizers were the most abundant sulfur oxidizers detected in both soils. Elemental sulfur fertilization caused an increase in populations of autotrophic thiosulfate-oxidizing micro-organisms, and a threefold increase in rhodanese and sulfur-oxidizing activity in a Waitville soil. In contrast, sulfur fertilization did not stimulate autotrophic thiosulfate oxidizers in a Loon River soil and the greatest increase in rhodanese and sulfur oxidation rates was only 31%. The response to sulfur application was biphasic however, and subsequent additions of sulfur fertilizer resulted in a decline in oxidation rates. Total sulfur content of sulfur-treated soils indicated that most of the sulfur applied was still present in the sampled zone. These results imply that prediction of sulfate release and fertilizer efficiency will be difficult to assess. Key words: Sulfur (elemental), S-oxidation, oxidation rates, rhodanese, sulfur-oxidizing micro-organisms