Hard Setting Soils

The problem of hardsetting soils is increasingly being recognized as a widespread form of land degradation in Australia and overseas. Hardsetting is a characteristic of soil horizons, usually cultivated seedbeds, which contain unstable soil aggregates. The instability of surface horizons in Australia is usually related to low levels of soil organic matter and/or high levels of exchangeable sodium (often remaining from when the profile was affected by salinity). Under rapid wetting by either rainfall or irrigation, the aggregates collapse, the seedbed slumps, and upon drying a hard, structureless mass of soil results. In surface horizons, it causes problems with infiltration, aeration, and seedling emergence. Lower in the profile, it causes problems of root elongation and waterlogging. This entry discusses the occurrence of hardsetting soils and the soil properties and processes that lead to the phenomena of hardsetting. Methods for the assessment and management of hardsetting soils are also presented.