There have been three main classification systems used in Northern Territory and Australia to describe soils. Great Soil Groups (for eg. Red Earths and Yellow Earths) were used along with a factual key (for eg. Gradational and Duplex Soils) from the 1970’s through to the 1990’s. Old reports will refer to these soils. Since 1996 all States and Territories have adopted The Australian Soil Classification.
The Australian Soil Classification describes fourteen soils orders across Australia with further subdivision under these broad groups. Some of these have not been described in the NT. The major soil orders across the Territory are listed below.
For further information on the Australian Soil Classification refer to the Australian Collaborative Land Evaluation Program website.
Australian Soil Classification (Isbell 2003)
Soil Orders Common across the NT
Soils that are massive and earthy (formerly red, yellow and brown earths). Throughout the NT; widespread across the Top End, Sturt plateau, Tennant Creek regions and Central Australia.
Very shallow soils or those with minimal soil development. Includes very shallow rocky and gravely soils across rugged terrain such as the Arnhem Plateau and also the sands of the Simpson Desert.
Weakly developed or sandy soils. Commonly shallow (slightly more developed than Rudosols), although they can include the deep sand dunes of beach ridges, granitic soils and sand dunes of deserts. Soils show some degree of soil profile organisation (minor colour or soil texture changes in subsoil).
Seasonally wet soils. Throughout the NT on floodplains, swamps, drainage lines but more common in higher rainfall areas. Includes mangrove and salt marsh environments.
Soils with an abrupt increase in clay content below the top soil. Restricted to small occurrences across plains and relict alluvial plains.
Soils with highly developed structural characteristics. Common across the Tindal area and also in the Daly River Basin.
Soils with calcium carbonate often formed on limestone. Restricted to small pockets in Central Australia, Victoria River District including Gregory National Park and Katherine and Mataranka Districts.
Iron rich soils generally formed on basalt. Restricted to volcanic landscapes of the Victoria River District and to a smaller extent in the Roper River Catchment.
Cracking clay soils which may or may not be poorly drained. Common across coastal floodplains of the Top End, the Barkly Tableland and alluvial plains of the Victoria River District.
Soil Orders less common across the NT
Soils high in sodium with an abrupt increase in clay content from the top soil to subsoil. Dispersive. Restricted to small occurrences in the southern region.
Soils resulting from human activities. Common in urban environments, industrial areas and mine sites
Soils with an abrupt increase in clay content from the top soil to subsoil and are strongly acid at depth.
Soils with high organic matter. Restricted to very small occurrences in peat swamps of some Top End floodplains. One known occurrence is on the edge of a back swamp of the Finniss River.
Soils with organic materials and aluminium with or without iron. Restricted to coastal heath areas along the Australian coastline.