Measurement of the oxidation rate of elemental sulfur in soil

Abstract

Equations have been derived for surface reaction rates for various shaped particles of known size distribution, assuming that the reaction rate per unit area was constant and that the effect of reaction products on the rate was negligible. These have been applied to the oxidation of elemental sulfur (So) in soil, assuming that the S° particles were either highly porous or were blocky shaped. Published incubation data for some New Zealand soils under pasture from five soil groups over a 70 day period and with up to 98% oxidation of added So were fitted with R2 of 95%. The average rate constants for the soil groups ranged from 48 to 76 S µg cm-2 day-1. These were similar to a value for an Australian soil, but 10-15 times greater than values for Canadian soils. The higher rate possibly resulted from the greater activity of thiobacilli, the reduction of lag time errors by long incubation times, and the avoidance of possible loss of oxidation products by direct determination of residual So. The addition of phosphate rock (50 g kg-1) gave an increase in rate for mineral soils, but not for organic soils, of 15 µg cmW2 day-1, and was attributed to enhanced aeration through better soil porosity.