EXTRACTABLE SULFATE IN 2 SOILS OF CONTRASTING PH AFFECTED BY APPLIED TOWN REFUSE COMPOST AND AGRICULTURAL WASTES

The effects of applied town refuse compost and two agricultural wastes on extractable SO42- were compared in one acid and one basic soil in an incubation experiment. The effects of addition of the wastes on elemental sulphur oxidation were also investigated. Town refuse compost added considerable amounts of SO42- to both soils in the earliest periods of study. Subsequent data, however, failed to show significant changes in the acid soil, thus indicating that the organic fraction of compost does not enhance sulphur mineralization. This behaviour was similar to that recorded for the low-sulphur agricultural waste. In the basic soil, SO42- values following the application of compost rose significantly in response to the mineralization process, parallelling to a certain extent that caused by the high-sulphur agricultural waste. Overall, the compost led to a significantly greater increase in SO42- than either of the two agricultural wastes throughout the experiment. The addition of compost or agricultural wastes to the acid soil increased the rate of elemental S oxidation. In general terms, both agricultural wastes significantly inhibited S oxidation in the basic soil, while town refuse compost failed to produce significant changes. Joint addition of agricultural wastes together with elemental S led to a drop in pH in both soils, which was especially notable in the acid soil. No such fall in pH occurred following the addition of town refuse compost and sulphur. © 1990.