A WORLD PERSPECTIVE ON ACID SULFATE SOILS

Generalizations about the morphology and genesis of acid sulphate soil s at a regional scale are derived from a review of extensive though pa tchy soil survey data. A general sequence of sedimentation, accumulati on of sulphides and burial of sulphitic material by peat or alluvium o f low sulphide content, and a parallel sequence of soil profile develo pment are illustrated by examples of unripe sulphitic soils under a na tural tidal regime, artificially drained raw acid sulphate soils and r ipe acid sulphate soils at various stages of development. The world pa ttern has been driven mainly by postglacial sea level change but each regional pattern is determined by its unique sedimentary and geomorpho logical history. Distinctive patterns occur in deltas and estuaries, a nd in humid and seasonally dry climates. Very extensive areas of ripe acid sulphate soils in areas that are not known to have experienced fa lls in relative sea level are ascribed to human activity: forest clear ance and soil erosion in catchments causing lower dry season river flo ws, and piecemeal clearance of peat over the floodplains permitting th e dry season water table to fall. The implications for further agricul tural development in other comparable areas include the absolute neces sity to know the extent of potential acid sulphate soils and to mainta in their water table above the sulphide datum. Most effective systems of management have been developed by farmers themselves but the sustai nability of these systems is often doubtful due to their detrimental e ffects on the aquatic ecosystem.