Soils what are we talking about?
GroundCover™ Issue: 40
The GRDC uses the terminology of the Australian Soil Classification (Isbell, 1996) as a standard frame of reference to soil type, because of its practical focus and clear descriptions of the ten main types found in Australia. The terms used in the ASC are the national standard, and provide a more definitive description of soil types and their properties than terms such as 'sandy loam '. The ASC terms will initially be unfamiliar to many growers (except perhaps for the well-known 'Vertosol'), but will gradually become the standard terms used in soil research and field trials. Below you'll find a list of the main ASC soil type names, together with a brief description. These images reflect soil types most likely encountered by farmers.
These soils contain calcium carbonate (as limestone, calcrete or other forms) as soft or hard fragments or as a solid layer. They occur in areas with low rainfall. Limitations for agriculture include shallow depth , low water retention and wind erosion on the sandier forms. High salinity, alkalinity and sodicity may also be a problem. Soil fertility deficiencies are widespread. Also known as solonised brown soils; grey-brown and red calcareous soils; calcareous sanlis.
Chromosols have an abrupt increase in clay content down the soil profile - they do not have high levels of sodium and are not strongly acidic in the subsoil. They occur in most districts and are common in the cereal belt of southern NSW and Victoria. Many Chromosols have hard setting surfaces with structural degradation caused by agricultural practices. These soils may have impeded internal drainage. Also known as non-calcic brown soils; some red-brown earths and a range of podzolic soils; some ironstone gravel soils.
Dermosols occur as moderately deep and well-drained soils in the wetter areas of eastern Australia. They are structured soils and may be strongly acid in the high-rainfall areas or highly alkaline if they contain calcium carbonate. Dermosols support a wide range of land uses, and cereal crops, especially wheat, are commonly grown on the more fertile examples. Also known as prairie soils; chocolate soils; some red and yellow pocizolic soils.
Ferrosols have high free iron and clay contents. They occur along the eastern coastline, in northern parts of WA and the Top End. In high-rainfall zones they may be very deep and well drained. They are not found widely in grain cropping regions. Despite being among the best soils for a wide range of agricultural pursuits, Ferrosols may be degraded by erosion and compaction caused by cropping practices and may also suffer from acidification. Also known as krasnoszems; chocolate soils.
Kandosols have uniform or gradual texture trends down the soil profile. They are mostly well drained, permeable soils, although some yellow and most grey forms have impeded subsoil drainage. They are common in all States except Victoria and Tasmania. Kandosols are used for extensive agriculture in the wheatbelt of southern NSW and south-west WA. Most Kandosols have low fertility and arc susceptible to surface soil degradation such as hard selling and crusting. Also known as red, yellow and grey earths; calcareous red earths.
These are strongly acid soils with an abrupt increase in clay down the soil profile. They extend from southern Queensland, through coastal and sub-coastal NSW to Tasmania, mainly in higher-rainfall areas. They arc less common in south-west WA, where small areas are used for cereal growing. Also known podzolic soils; texture contrast soils.
Rudosols are a widespread and diverse group of very young soils. Most have few commercial land uses because of their properties or occurrence in arid regions, or both. The largest areas occur in the desert regions of arid central and north-west Australia. In contrast, fertile variants formed in alluvium arc used for cropping. Also known as lithosols; alluvial soils; calcareous and siliceous sands; shallow stony soils; deep sands.
Sodosols have an abrupt clay increase down the profile and high sodium content, which may lead to clay dispersion and instability. Seasonally perched watertables are common because of the structure of the subsoil. These soils are usually associated with a dry climate and they are widely distributed in the eastern half of Australia and the western pOrlion of WA, where they are used extensively for grain crops. These soils are usually very hard when dry, are prone to crust formation and have subsoil constraints to root growth. The dispersivc subsoil makes them prone to tunnel and gully erosion. Also known as red-brown earths; desert soils; texture contrast soils.
Widespread in the western half of the continent where vast areas occur as red and yellow sandplains. Large areas in WA have red loamy soils with a redbrown hardpan at shallow depths. Due to their poor water retention, almost universally low fertility and occurrence in regions of low and erratic rainfall, Tenosols are mainly used for grazing of native pastures rather than cropping. Also known as lithosols; some alluvial soils; shallow stony soils; deep sands.
These soils shrink and swell, and crack as the soil dries. extensive dry land agriculture where rainfall is adequate, and irrigated agriculture. Problems of water entry are usually related to tillage practices and adverse soil physical conditions at least partly induced by high sodium in the upper parl of many proliles. Also known as black earths; grey, brown and red clays; cracking cluys.
Several other soil types are less commonly used for agriculture. They include Hydrosols (seasonally wet or permanently wet soils), Organosols (organic soils mainly in coastal or alpine regions), Podosols (usually infertile sandy soils with organic materials and aluminium, with or without iron) and Anthroposols (soils resulting from human activity).
Isbell, R.F. (1996) The Australian Soil Classification (CSIRO Publishing: Melbourne).
Isbell, R.F., McDonald, W.S. and Ashton. L.J. (1997) Concepts and Rationale oj the Australian Soil Classification (ACLEP, CSIRO Land and Water: Canberra).
Peverill, K.I., Sparrow, L.A. and Reuter, D.J. (eds) (1999) Soil Analysis: An Interpretation Manual (CSIRO Publishing: Melbourne).
A large coloured wall poster showing the main soil types of Australia is available from CSIRO Publishing. Useful web sites include: http:// www.publish.csiro.au/(go to the soil science category); and www.grdc.com.au.
A forthcoming CSIRO Land and Water publication, Australinn Soil by Neil McKenzie, Ray Isbell, David Jacquier and Katharine Grown, is due for release later this year.