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Acid sulfate soil

What are acid sulfate soils?

Acid sulfate soils are naturally occurring sediments and soils containing iron sulfides (principally pyrite) and/or their precursors or oxidation products. The exposure of the sulfides to oxygen by drainage or excavation leads to the generation of sulfuric acid.

‘Acid sulfate soils’ include actual acid sulfate soils and potential acid sulfate soils. Actual and potential acid sulfate soils are often found in the same soil profile, with actual acid sulfate soils generally overlying potential acid sulfate soil horizons.

‘Actual acid sulfate soils’ are soils containing highly acidic soil horizons or layers resulting from the oxidation of soil materials that are rich in sulfides, primarily pyrite. This oxidation produces acidity in excess of the sediment's capacity to neutralise the acidity resulting in soils of pH4.0 or less.

‘Potential acid sulfate soils’ are soils that contain iron sulfides or sulfidic material that has not been exposed to air and oxidised. The field pH of these soils in their unoxidised state is more than 4.0. They may be neutral or slightly alkaline.