Main soil types in Australia

Summary

This article describes ten of the most common soil types in Australia.

Introduction

The three most important factors for determining soil types are parent material, annual rainfall and topography. Parent material is the material that soil develops from such as rock, or material that has been deposited by wind or water. The characteristics of the parent material are important in determining the physical and chemical properties of the soil. Other factors that determine a soil’s characteristics include climate, organic activity and time. Ten of the common Australian soils with some of their characteristics are described in this article.

Podosol

Parent material is extremely siliceous with rainfall over 700mm and sites either well-drained (mid and upper slopes) or poorly drained (footslopes and flats). The B horizon of a Podosol is dominated by compounds of organic matter, Al and/or Fe (generally highly sandy and acidic). Generally, podosols have very low agricultural potential with very low chemical fertility, structure and water-holding capacity. However groundwater contamination is a potential problem due to high permeability.

Tenosol

Parent material of Tenosols is extremely or highly siliceous with rainfall from 0 to 1400mm on well-drained sites or 0 to 1100mm on poorly drained sites. Tenosols have a weak soil profile which is typically very sandy with surface soils often very acidic. Generally, tenosols have a very low agricultural potential with very low chemical fertility, poor structure and low water-holding capacity. However ground-water contamination can be a potential problem due to the high permeability of these soils. Tenosols have strong texture contrast with strongly acid B horizon which may or may not be sodic. (Sodic soils are high in sodium, easily lose their structure when wet.) The surface soils are often acidic.

Kurosol

Parent materials of Kurosols range from highly siliceous, siliceous to intermediate in composition, with rainfall from 50 to 1350mm in poorly drained sites or 750 to 1300mm on well-drained sites. They have a strong texture contrast with strongly acid B horizon which may or may not be sodic. The surface of Kurosol soils are often acidic. They generally have very low agricultural potential with high acidity (pH < 5.5) and low chemical fertility. Kurosols commonly have low water- holding capacity and are often sodic.

Sodosol

Parent materials of Sodosols range from highly siliceous, siliceous to intermediate in composition. Sodosols are only found in poorly drained sites with rainfall between 50mm and 1100mm. Sodosols show strong texture contrast with highly sodic B horizon but they are not highly acidic (pH > 5.5). Generally, sodosols have very low agricultural potential with high sodicity leading to high erodability, poor structure and low permeability. These soils are have low to moderate chemical fertility and can be associated with soil salinity.

Chromosol

The parent material of Chromosols ranges from highly siliceous, siliceous to intermediate in composition. These soils are found in imperfectly drained sites (yellow and grey chromosol) with rainfall between 250mm and 900mm. They are also found in well-drained sites (brown and red chromosol) with rainfall between 350mm and 1400mm. Chromosols have strongly contrasting texture. They are not strongly acidic or sodic in the upper B horizon. 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.

Kandosol

Parent material of Kandosols ranges from highly siliceous, siliceous to intermediate in composition. These soils are found in poorly drained sites (yellow and grey kandosol) with rainfall between 300mm and 1400mm and in well-drained sites (brown and red kandosol) with rainfall between 250mm and 1400mm. Kandosols do not have a strong texture contrast. Thy are massive or weakly structured B horizon and are not calcareous. Generally, Kandosols are low to moderate in agricultural potential with moderate chemical fertility and water-holding capacity.

Calcarosol

Parent material ranges from highly siliceous, siliceous to intermediate in composition. Found in imperfectly drained sites with rainfall between 0mm and 400mm and in well-drained sites with rainfall between 250mm and 500mm. Calcarosols are calcareous throughout and do not have a strong texture contrast. Generally, 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.

Dermosol

The parent material or dermosols ranges in composition from siliceous, intermediate and mafic (rich in Mg and Fe, as well as in many other nutrients), generally dark and very hard. Found in imperfectly drained sites (yellow and grey dermosols) with rainfall between 550mm and 1350mm and in well- drained sites with rainfall between 450mm and 1200mm. These soils do not have strong texture contrast. They have a well structured B2 horizon containing low levels of free iron. Dermosol generally have high agricultural potential with good structure and moderate to high chemical fertility and water-holding capacity with few problems.

Ferrosol

The parent material of ferrosols is intermediate or mafic in composition. These soils are only found in well-drained sites with rainfall between 700mm and 1450mm. They do not have a strong texture contrast. Their B2 horizon has high free iron oxide (Fe >5%). Mostly, they are well structured. Ferrosols have high agricultural potential because of their good structure and moderate to high chemical fertility and water-holding capacity. Their high rainfall equivalents (Krasnozems) may suffer from acidification and nutrient leaching. They also have potential for structural decline.

Vertosol

The parent material of Vertosols ranges from intermediate, mafic and ultramafic in composition. These soils are found in imperfectly drained sites (black vertosol) with rainfall between 0mm and 1150mm and in well-drained sites (red vertosol) with rainfall between 0mm and 900mm. Verticols have a uniform texture, clay- rich soils (>35%). They have the potential for strong cracking and slickensides. 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 required to improve their structure. Heavy plastic clays can be difficult to cultivate especially when they are wet. Shrink-swell phenomena also creates problems for foundations of buildings build on Verticols.

Reference

Gray JM, Murphy BW and Chapman GA (2002). Predicting Soil Distribution, Joint DLWC and ASSSI Technical Poster, DLWC, Sydney.

 

 

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