Effect of nutrients and elemental sulfur particle size on elemental sulfur oxidation and the growth of Thiobacillus thiooxidans

Abstract

Elemental sulfur (S) has many attractions as a fertiliser but it must be oxidised to sulfate before it is plant available. Two laboratory incubation experiments with a high S sorbing basaltic soil (Haplohumult) from Walcha, New South Wales, are reported here. The first experiment was conducted to study the effect of – P and other nutrients on the oxidation of elemental S and the growth of Thiobacillus thiooxidans. The second experiment studied the effect of phosphorus (P) rate, elemental S particle size, and elemental S form on the oxidation of elemental S at different times.

There were significant differences between treatments in the percentage and amount of elemental S oxidised, with the lowest oxidation occurring during the 6-week incubation in the P treatment, which represented 1·8% of the applied S compared with 16·0% when all nutrients were supplied. There was a significant linear relationship between T. thiooxidans population at the end of the incubation period and the amount of elemental S oxidised.

The oxidation of elemental S was higher when fine (50–150 µm) particle size elemental S was used, compared with coarse (150–250 µm) elemental S. There was no clear difference in oxidation rate between ground and recrystallised elemental S. The S oxidation rates recorded in these experiments were compared with those predicted by an S oxidation model and found to be in close agreement.