The ASC is Australia’s national system of soil classification. The ASC divides the soils of Australia into the following classes, known as Orders:
Anthroposols result from human activities which cause significant modification, mixing, truncation or burial of original soil layers, or creation of new soil materials. This anthropic disturbance excludes normal agricultural operations, and sealing or semi-sealing of surfaces, such as roads and hardstanding
Calcarosols are soils that contain significant amounts of carbonate and have significantly more clay in their subsoils than in their topsoils. These soils are naturally alkaline, particularly in the subsoil. The carbonates in the soil may be formed from shell deposits, from fragments of underlying rock such as limestone, or from soft nodules, hard nodules or pans.\n\nGenerally, they have low to moderate agricultural potential with low chemical fertility and water-holding capacity. They often have high salinity levels, alkalinity and boron toxicity.
Chromosols are soils with significant increase in clay content between topsoil and subsoil, but are not strongly acidic or sodic (see Sodosols). These soils are found in imperfectly drained sites (Yellow and Grey Chromosol) where rainfall is between 250–900 mm. They are also found in well-drained sites (Brown and Red Chromosols) with rainfall between 350–1400 mm. These soils have moderate agricultural potential with moderate chemical fertility and water-holding capacity. They can be susceptible to soil acidification and soil structure decline. Red Chromosols are amongst the most widespread soils used for agriculture in Australia.
Dermosols are soils with structured subsoils and without a strong increase in clay content between topsoils and subsoils. These soils are found in imperfectly drained sites (Yellow and Grey Dermosols) with rainfall between 550–1350 mm and in well-drained sites with rainfall between 450–1200 mm. Dermosols generally have high agricultural potential with good structure, and moderate to high chemical fertility and water-holding capacity with few issues relating to their use or management.
Ferrosols are soils with high levels of free iron oxide in their subsoils, and without a strong increase in clay content between topsoils and subsoils. These soils have high agricultural potential because of their good structure and moderate to high chemical fertility and water-holding capacity. Ferrosols with high rainfall (formerly classified as Krasnozems) may suffer from acidification and nutrient leaching. They also have potential for structural decline. The soils developed on basalt and similar basic volcanic rocks in north-east NSW are examples of Ferrosols.
Hydrosols are soils that are seasonally or permanently waterlogged, involving saturation of the soil with water for at least 2–3 months in most years. These soils may or may not experience reducing (anoxic) conditions while saturated, whilst some Hydrosols, such as those found in mangrove swamps, are highly organic.
Kandosols are soils without a strong increase in clay content between topsoil and subsoil, without strong structure in the subsoil, and which are not calcareous (see Calcarosols). These soils are found in poorly drained sites (Yellow and Grey Kandosols) with rainfall between 300–1400 mm and in well-drained sites (Brown and Red Kandosols) with rainfall between 250–1400 mm. Generally, Kandosols have low to moderate agricultural potential with moderate chemical fertility and water-holding capacity.
Kurosols are soils with a strong increase in clay content between topsoil and subsoil, and with strongly acidic subsoils. This inherent acidity can also result in other chemical issues, such as high magnesium, sodium and aluminium concentrations, that can inhibit plant growth. Kurosols generally have very low agricultural potential with high acidity (pH less than 5.5) and low chemical fertility. Kurosols commonly have low water-holding capacity and are often sodic.
Organosols are soils dominated by organic materials, with either at least 0.4 m of organic materials within the uppermost 0.8 m of the profile or at least 0.1 m of organic materials directly overlying the substrate.
Podosols are soils dominated by the accumulation of compounds of organic matter, aluminium and/or iron, and are typically very deep and sandy, with one or more subsoil layers showing strong accumulation of these materials (e.g., iron or coffee rock pans). Generally, Podosols have very low agricultural potential with very low chemical fertility, structure and water-holding capacity. Groundwater contamination is a potential problem due to high permeability.
Rudosols are relatively young soils in which soil-forming processes (such as chemical weathering, erosion or deposition) have had little time to modify them. This classification includes soils with a wide variety of textures and depths, as they may have been formed by very different processes.
Sodosols are soils with a strong increase in clay content between topsoil and subsoil, and subsoils that are not strongly acidic and have high sodium content. Such ‘sodic’ soils tend to have poor structure which limits or prevents water infiltration and impedes drainage, and which tend to be highly dispersive and vulnerable to soil erosion. They can be acidic, neutral or alkaline and may also be highly saline (containing hazardous amounts of salt, inhibiting plant growth and productivity). Sodosols are only found in poorly drained sites with rainfall between 50–1100 mm. Generally, they have very low agricultural potential where high sodicity leads to high erodibility, poor structure and low permeability. These soils have low to moderate chemical fertility and can be associated with soil salinity.
Tenosols are soils with only weak development of soil layers apart from their topsoils, but are otherwise quite variable. Generally, Tenosols have a very low agricultural potential with very low chemical fertility, poor structure and low water-holding capacity. Groundwater contamination can be a potential problem due to the high permeability of these soils.
Vertosols are clay-rich soils with shrink-swell properties (clays that swell when wet and shrink again as they dry out) and exhibit strong cracking when dry. These soils have high agricultural potential with high chemical fertility and water-holding capacity, but they require significant amounts of rain before water is available to plants. Gypsum and/or lime may be used to improve their structure. They can be difficult to cultivate especially when wet. The clays swell when wet and shrink when dry, which can lead to problems for foundations of buildings. The highly productive ‘black soils’ of the Liverpool Plains in northern NSW are a good example of Vertosols.
For more information about the ASC, see soilscienceaustralia.org.au/asc. More maps and information about soil types in NSW are available on eSPADE at espade.environment.nsw.gov.au