Sulphur measurements made on soils in East Africa revealed the unexpected occurrence of sulphates in forest subsoils. Soil profiles from plantation and natural forests were analysed and a general pattern of sulphur distribution was found.
It has been found that in addition to the sulphur cycle dependent upon microbiological oxidation of organic sulphur there exists a cycle whereby sulphate is circulated as such between trees and soil.
The biological oxidation of organic sulphur in the soil is an extremely slow process compared with that of carbon and nitrogen. Treatment with calcium carbonate, nitrates and non-sulphur-containing amino acids had no effect upon the subsequent sulphate production. Incubation with either S-containing amino acids or with calcium sulphate however, resulted in an increased rate of soil-sulphur oxidation and this effect is being further investigated.
An aqueous extract of wattle leaves proved to inhibit nitrification in the soil for short periods and evidence is presented which suggests that methionine may be involved in this effect.