Soils - Overview
Overview
Why are soils important?
Soil is the main resource upon which the 'natural environment' and agricultural production depend. It provides many construction materials and is the foundation for our urban and recreational facilities.
Australian soils have been subject to extensive degradation due to such practices as overgrazing, over cultivation, tree clearing, and irrigation. A continuous cover of vegetation on the soil results in the most stable situation. However this is not possible for many land uses, particularly those in the agricultural sector.
Major forms of degradation:
- wind and water erosion
- reduced fertility because of nutrient loss
- physical breakdown of soil structure
- soil acidification
- salinisation
Managing the future of Australia's soil resources requires a knowledge and understanding of the resource: its distribution, condition and extent.
Australian agricultural soil characteristics
Australian soils tend to be:
- old
- salty
- clayey - except in the west of the continent where they tend to be sandy
- acidic
- nutritionally and organically impoverished
- structurally challenging
Compared with soils in the Northern Hemisphere, Australian soils have less organic matter and poor structure and tend to be quite clayey just below the surface, which restricts drainage and impedes root growth. Some of the clay characteristics cause problems for engineering and farming because of their 'shrink and swell' nature.
Australian soils mirror the continent's great age and consequently are products of environmental conditions throughout history (climate, organisms, topography, parent material and time). This means that large areas are affected by salt and have various nutrient and physical limitations for plant growth and agriculture.
The agricultural landscapes of Australia support a great range of soils. Most are ancient, strongly weathered and infertile. Others are younger and more fertile. This variety along with the natural limitations of many soils and their interactions with climate, have made it difficult to develop sustainable systems for agriculture. Limitations to productivity have also been induced through human impacts on soils. While some forms of degradation such as nutrient deficiencies can be corrected, others, such as soil erosion, are difficult to remedy.
The terminology of the Australian Soil Classification (Isbell 1996) is used here as a frame of reference because of its practical focus and descriptions of the ten main soil orders used for agriculture are provided below. A generalized map of soil orders is shown in the next section.
Australian soils have many distinctive features. Surface layers have low contents of organic matter and most are often poorly structured, a condition made worse by various agricultural practices. Subsurface layers with a sharp increase in clay content are widespread (Kurosol, Chromosol and Sodosol soil orders) and they can restrict drainage and root growth. In these soils, bleached layers with very low nutrient levels are also common. Soils affected by salt, either now or in earlier geological times, cover large portions of the arable lands of the continent (Sodosols) and they have various nutrient and physical limitations.
Australia is also notable because of the very large areas of cracking clays (Vertosols). These are relatively fertile but exhibit physical limitations. Soils formed in aeolian sands (Rudosols and Tenosols) fringe the southern cropping lands but are more extensive in the arid zone. Finally, the remaining ancient landsurfaces, particularly in northern Australia have very deep and strongly weathered soils (Kandosols) with very low levels of nutrients.
Soils with calcium carbonate: Calcarosols
These soils contain calcium carbonate as soft or hard fragments or as a solid layer. They occur in areas with low rainfall and are used for cereal growing and irrigated horticulture in the south and sparse grazing in the north. 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.
Acidic soils with an abrupt increase in clay: Kurosols
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 New South Wales to Tasmania. They are less common in southwest Western Australia. Some areas have been cleared and used for dairying on improved pastures. In the higher rainfall areas of New South Wales and Tasmania, Kurosols are used for forestry. Small areas in Western Australia are used for cereal growing and lower rainfall areas with woodland support sparse grazing.
Soils high in sodium and with an abrupt increase in clay: Sodosols
Sodosols have an abrupt clay increase down the profile and high sodium content, which may lead to clay dispersion and instability. Seasonally perched water tables 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 portion of Western Australia. Common land-uses include grazing of native or improved pastures for both dryland and irrigated agriculture, and forestry. These soils are usually very hard when dry and are prone to crust formation. The dispersive subsoil makes them prone to tunnel and gully erosion.
Soils with an abrupt increase in clay: Chromosols
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 New South Wales and Victoria. Land use in the tropics is mainly cattle grazing of native pastures. Many Chromosols have hardsetting surfaces with structural degradation caused by agricultural practices. These soils may have impeded internal drainage.
Structureless soils: Kandosols
Kandosols 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 New South Wales and southwest Western Australia. In the better-watered areas they are used for a range of horticultural crops. Most have low fertility and land use is restricted to grazing of native pastures. Grazing lands are susceptible to surface soil degradation such as hardsetting and crusting even though grazing intensity is low.
Weakly developed soils: Tenosols
Widespread in the eastern half of the continent where vast areas occur as red and yellow sand-plains. Large areas in Western Australia have red loamy soils with a red-brown 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 the grazing of native pastures. In the better-watered areas landform prevents cultivation, but limited areas support forestry (east coast and southwest Western Australia).
Structured soils: Dermosols
Dermosols occur as moderately deep and well-drained soils in the wetter areas of eastern Australia. They 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 including cattle and sheep grazing of native pastures, forestry and sugar cane. Cereal crops, especially wheat, are commonly grown on the more fertile Dermosols.
Iron rich soils: Ferrosols
Ferrosols have high free iron and clay contents. They occur along the eastern coastline, in northern parts of Western Australia and the Top End. In high rainfall zones they may be very deep and well drained. Land use includes dairying on improved pastures, horticultural crops, some plantation forestry, and sugar cane in Queensland. In northern Australia the shallow and stony soil types support beef cattle grazing. Despite being amongst 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.
Minimal soil development: Rudosols
Rudosols are a widespread and diverse group of 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 northwest Australia and support grazing of native pastures. In contrast, fertile variants formed in alluvium are used for cropping and improved pastures. Some dune soils of the Riverine Plain in the Murray-Darling Basin are irrigated for citrus and vines.
Shrink and swell clay soils: Vertosols
These soils shrink and swell, and crack as the soil dries. Vertosols are used for grazing of native and improved pastures, extensive dryland 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 part of many profiles.
Soil orders rarely used for agriculture:
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).
Which soils are where and how are they used?
Typically, maps are used to provide pictorial representations of the distribution of Australian soils, each map varying according to the specific soil classification scheme used.
The map below shows the soils of Australia classified using the Australian Soil Classification , which is the current national standard. Click here for more information on soil classification
The table below show the areas (hectares) of different soil types (ASC soil order) in each State and Territory.
| Qld | NT | NSW | WA | SA | Tas | Vic | |
|---|---|---|---|---|---|---|---|
| Calcarosol | 1108600 | 1862100 | 7458000 | 24900900 | 32000300 | 2953600 | |
| Chromosol | 7904700 | 545200 | 4198700 | 5452600 | 1756500 | 233100 | 2908000 |
| Dermosol | 3978600 | 534800 | 3245400 | 511000 | 42900 | 1373800 | 2496500 |
| Ferrosol | 2333100 | 535600 | 954800 | 1787400 | 357000 | 237200 | |
| Hydrosol | 5072100 | 2848200 | 248600 | 8145000 | 106200 | 91700 | |
| Kandosol | 42050100 | 27744200 | 21105800 | 29888400 | 6886600 | 76000 | |
| Kurosol | 1501300 | 2732200 | 491900 | 249000 | 853000 | 875800 | |
| Organosol | 28100 | 8800 | 2700 | 750600 | 35300 | ||
| Podosol | 610800 | 156000 | 1028300 | 150100 | 235100 | 524200 | |
| Rudosol | 13558900 | 36030400 | 1058700 | 34158700 | 22098900 | 112100 | 174400 |
| Sodosol | 24207300 | 2848900 | 17497600 | 28167000 | 17121100 | 1341500 | 8406800 |
| Tenosol | 21434100 | 48840700 | 4141100 | 113960800 | 10495200 | 1389900 | 1557000 |
| Vertosol | 48498700 | 12581700 | 17163900 | 3528900 | 4449700 | 16400 | 2180800 |
| Total | 172447100 | 134371800 | 80234800 | 252037500 | 98134600 | 6698600 | 22637500 |
Soils and land use
It seems obvious that soil type and properties should be fundamental in determining land use, particularly in agriculture. To some extent, this is true - a characteristic of the Australian landscape is that uncleared areas in the agricultural zone are often areas with poor soils. In practice, though, many other factors control agricultural land use - for example climate, water supply and proximity to markets. Areas with soils which are not highly suitable for agriculture are likely to be farmed if other factors are favourable.
In some cases, soil limitations can be managed - for example, application of fertilisers to soils of low fertility, and use of conservation farming techniques on soils with high erodibility. However, inappropriate land use is the major driving factor in land degradation. A better understanding of the distribution of land use relative to soil type is crucial in designing and implementing sustainable land use systems.
Tables below broadly shows the current (1996/97) land use on different soil types nationally.
| Conservation and natural environments | Production from native environments | Dryland agriculture and plantations (excluding horticulture) | Horticulture | Irrigated agriculture and plantations (excluding horticulture) | Built environment | Other | Total area | % of Australian land surface | |
| Calcarosol | 23873700 | 41868100 | 3655400 | 53600 | 41800 | 84200 | 706700 | 70283500 | 9.2% |
| Chromosol | 2782000 | 15588300 | 4328500 | 35500 | 59100 | 148700 | 56700 | 22998800 | 3.0% |
| Dermosol | 3640400 | 7300600 | 943400 | 24400 | 61200 | 134600 | 78400 | 12183000 | 1.6% |
| Ferrosol | 1584300 | 3929700 | 552100 | 21500 | 21100 | 75800 | 20600 | 6205100 | 0.8% |
| Hydrosol | 5256500 | 6515100 | 357900 | 8200 | 17400 | 91600 | 4265100 | 16511800 | 2.2% |
| Kandosol | 31913500 | 89899600 | 5085700 | 21200 | 114300 | 223300 | 493500 | 127751100 | 16.7% |
| Kurosol | 1963800 | 3435900 | 1007100 | 24500 | 34800 | 209400 | 27700 | 6703200 | 0.9% |
| Organosol | 669300 | 47900 | 13000 | 300 | 1100 | 10800 | 83100 | 825500 | 0.1% |
| Podosol | 987900 | 898700 | 576100 | 9100 | 15300 | 139200 | 78200 | 2704500 | 0.4% |
| Rock | 34100 | 55700 | 200 | 0 | 300 | 90300 | 0.0% | ||
| Rudosol | 64371700 | 41731200 | 421100 | 4200 | 9500 | 109800 | 544600 | 107192100 | 14.0% |
| Sodosol | 12206500 | 68677000 | 16318500 | 67500 | 995400 | 700900 | 624400 | 99590200 | 13.0% |
| Tenosol | 108760800 | 88825500 | 2746100 | 15700 | 48700 | 362900 | 1059100 | 201818800 | 26.3% |
| Vertosol | 5912400 | 74889200 | 5211900 | 35300 | 512100 | 91200 | 1768000 | 88420100 | 11.5% |
| Total | 264077100 | 443893300 | 41240800 | 321600 | 1932400 | 2385400 | 12711300 | 766561900 |
What is soil and how do we describe them?
Gardeners, farmers, engineers, builders, hydrologists, conservationists, geomorphologists, geologists, pedologists all have their own take on soil. The gardener or farmer sees the soil as a medium for growing plants and is mainly interested in obtaining the best possible plant growth from a particular soil. The degree to which soil will absorb or shed rainfall or transmit water across a landscape is what matters to a hydrologist. Soil is seen as a construction material or foundation by engineers and builders but to the pedologist, geomorphologist or geologist, soils are primarily the unconsolidated materials at the earth's surface, derived from particular parent materials and influenced by various physical and chemical processes. Conservationists view soil as a fragile resource to be conserved because it is often degraded when used beyond its capacity. [Based on Murphy, B.W. (1991) The nature of soil. In Soils their properties and management: a soil conservation handbook for New South Wales. Sydney Uni Press.]
Soils are developed by physical, chemical and biological processes including the weathering of rock and the decay of vegetation. Soil materials include organic matter, clay, silt, sand and gravel, mixed together to form a medium in which most plants grow. Soil typically comprises several layers (called horizons), more or less parallel to the earth's surface, which together make up the soil profile.
Soil profiles and soil horizons
Soils are often described in terms of the soil profile (see example below) - that is, a vertical section of soil in which various soil properties can be observed.
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Photograph of a typical profile from Southern Murray Mallee, South Australia. Photograph acknowledgment: Primary Industries and Resource South Australia, Site MM035 |
A soil horizon is a layer of soil with morphological properties different from layers that are below or above it in the profile. The major types of horizons are as follows (definitions from the Australian Soil and Land Survey Field Handbook)
- O Horizons
- A Horizons - A1, A2, A3
- P Horizons
- B Horizons - B1, B2, B3
- C Horizons
- D Horizons
- R Horizons
Soils are often discussed in terms of topsoil and subsoil. These terms are not rigorously defined, but denote:
- topsoil - the surface zone, including the zone of accumulation of organic material (usually the A horizons). Topsoil can be modified by management practices, such as ploughing and addition of fertilisers
- subsoil - underlying layers (B and C horizons), which cannot usually be modified except by drainage.
Soils nearly always have some degree of layering. The layering may be inherited from the parent material; for example, soils on alluvial flats with regular flooding often have clear sedimentary layers. Inherited layering can also be due to other forms of sedimentation or reflect patterns in the rock from which the soil has formed.
Various soil-forming processes create and destroy layers and it is the balance between these competing processes that will determine how distinct layers are in a given soil. Some of the more common processes include the actions of soil fauna (worms, termites etc), and the depletion and accumulation and constituents including clay, organic matter and calcium carbonate.
Soil layer definitions are as numerous as the layers themselves. The following have been adapted from the Australian Field Handbook (McDonald et al. 1990) and are well accepted.
O Horizons are dominated by organic matter that has accumulated on the surface of the soil. O horizons are subdivided according to the degree of organic material decomposition. These horizons are not common and are mostly restricted to moist or cool environments (eg. alpine areas, swamps, rainforests)
A Horizonsconsist of one or more surface mineral horizons with some accumulation of organic materials (less than O horizons). A horizons are usually darker than underlying horizons but they may also be horizons that are lighter coloured or have a lower content of clay when compared to underlying horizons. There are three types of A horizon:
- The A1, which is a mineral horizon at or near the soil surface that has some accumulation of organic matter. It is usually darker than the underlying horizons and it is the zone of maximum biological activity.
- The A2, which is a mineral horizon that has less organic matter, sesquioxides or clay than the horizons above or below. It is a pale horizon and is common throughout Australia. Various degrees of bleaching are recognized with white or near white layers being referred to as sporadically or conspicuously bleached depending on its extent.
- The A3 which is a transitional horizon between A and B horizons.
P Horizons are dominated by organic materials in various stages of decomposition that have accumulated in either under water or in very wet areas. They are often referred to as peat layers.
B Horizons have one or more of the following:
- concentration of clay, iron, aluminium or organic material;
- a structure or consistence unlike the A horizon above and different to the horizons below; or
- stronger colours than the horizons above or below.
- The B1 horizon is a transitional layer between the A and B horizons but it is more like the B horizon. Similarly, a B3 horizon is a transitional layer to the underlying material.
C Horizons are layers below the A and B horizons that are composed by consolidated or unconsolidated materials. These materials are usually partially weathered and geological features are often evident. C horizons can be dug by hand when they are moist.
D Horizons are soil layers below the A and B horizons that differ in general character and are not C horizons. They cannot be reliably described as buried soils but have a contrasting pedological organization to the overlying horizons.
R Horizons are continuous masses of rock that are usually too strong to dig with hand tools.
Soil properties
Various easily recognisable properties - such as depth, texture, pH, nutrient status, colour and structure - are used to differentiate soils. Characteristic properties may be:
By analysing a soil's properties - usually by means of a soil profile - it is possible to determine how suited it is to particular uses or remediation strategies. For most practical problems, it is very important to understand how soil properties and soil profiles vary across the landscape.
Morphological properties - the look and feel of a soil
Soil morphological properties are those that can be seen, felt, sometimes heard, and occasionally smelt or tasted. They include the:
- thickness of soil layers (horizons),
- texture,
- colour,
- shape and size of soil aggregates, and
- accumulations of particular compounds such as organic matter.
Morphological properties can be described in the field using relatively simple methods and with careful interpretation, a good quality description of a soil profile's morphology can provide useful insights into:
- how the soil has formed;
- current landscape processes (eg. whether waterlogging occurs);
- land suitability for a range of uses;
- current soil condition; and
- limitations and hazards of use.
Chemical properties
Chemical properties contribute to the status of the soil solution - the water in soil with its varying quantities of ions. The soil solution contains nutrients necessary for plant growth, the products of weathering and other soluble salts. The chemical properties of soil largely depend on the chemical composition of the parent materials and on the nature of the processes of formation. Through the recycling of organic matter as part of the soil formation process, vegetation also contributes to soil chemical properties.
Chemical properties of soil which are routinely analysed include:
- soil nutrients (for example, nitrogen, phosphorus, potassium)
- cation exchange capacity (CEC)
- acidity / alkalinity (pH)
- sodicity
- trace elements (for example, copper, manganese).
Understanding soil chemical properties can provide useful insights into:
- the nature and management of soil salinity, fertility and acidity
- diagnosing the constraints to plant growth
- making decisions about the application of fertilisers and soil conditioners for agricultural production.
Physical properties
Soil physical properties are at least as important as soil chemical properties in determining soil fertility. They determine the soil-water regime, aeration, ease of root growth (strength x water content) and temperature (less important). Unlike soil chemistry, there have been no routine programs of measurement for soil physical properties because they are more difficult to measure (undisturbed soil cores are usually required and laboratory measurements can take months). Consequently there are no databases available to provide reliable maps of soil physical properties - instead, indirect methods are used to estimate soil physical properties such as permeability, soil water storage and aeration. This requires understanding concepts about the soil's particle size and distribution, its bulk density and air and water storage characteristics, and impediments to root growth.
Important physical properties include:
- particle size distribution
- bulk density / strength characteristics
- water holding capacity
- permeability
Particle size distribution strongly influences the physical and chemical behaviour of soil. The particle size distribution indicates the relative proportions of mineral particles of various sizes (i.e. clay, silt and sand). These influence the surface area and charge characteristics of soils which in turn determine a range of soil properties including fertility, bearing strength, permeability, erodibility and susceptibility to pollution. Although an approximate estimate of particle size distribution can be obtained from field texturing, reliable determination requires laboratory analysis.
Bulk density is a measure of soil porosity and is needed to calculate soil water and nutrient content. A low bulk density indicates high pore space and greater potential to store water. Roots extend more readily through a soil of low bulk density. Root growth can be impeded when soil is too strong or there are insufficient cracks or pores to allow root extension. The strength of soil is very dependent on water content and it increases as the soil dries. In many Australian soils, excessive strength impedes root growth at water contents above the wilting point. As a result, roots cannot grow and extract water even though the soil layer is above wilting point. Subsoil compaction caused by heavy machinery can make this problem worse and it reduces the water use efficiency of agricultural systems. There are few data on the strength characteristics of Australian soils. However, impedance to root growth occurs when soil strength exceeds a penetration resistance of 3.5 MPa. As a guide, this is roughly the maximum pressure that can be applied by the palm of the hand when pushing a pencil into soil.
The capacity of a soil to supply air and water is determined by its porosity and ability to retain water. The water retention ability of a soil is measured by the suction and water content relationship. The maximum suction that roots can apply before a plant wilts due to inadequate water is very similar between species. In sandy soils, very little water will be left in the soil at wilting point because the pores between sand grains are large and the water can be extracted more readily. In clay soils, the pores are much smaller and capillary forces result in more water being retained when plants wilt. The physical fertility of a soil is heavily influenced by the balance between the size of the water store and the proportion of air filled pores at field capacity.
The permeability of a soil, in conjunction with its water storage capacity, is fundamental to controlling the soil water regime which, in turn, controls ecosystem processes and land suitability for a range of purposes. The hydraulic conductivity of a soil is a measure of its permeability: soils with a slow hydraulic conductivity at or near the soil surface (e.g. less than 30 mm/hr) cannot transmit water from heavy showers of rain and this can lead to excessive runoff and erosion. Runoff also represents a loss of water that could have otherwise been available to plants. Subsoil layers are nearly always less permeable than surface layers because of the lower rates of biological activity. Soils with sharp texture contrasts and well developed A2 horizons often have a sharp reduction in hydraulic conductivity with depth and drainage of water is often impeded and periodic saturation of water can occur. Hydraulic conductivity is in large measure controlled by the texture and structure of a soil layer. Therefore sandy soils are nearly always very permeable but the converse is not true. Some clay soils can be more permeable than sands (e.g. Red Ferrosols) because of their strongly aggregated structure. Other clay soils (e.g. most Vertosols and the B horizons of Sodosols) are very impermeable.
Biological properties
A vast assemblage of organisms naturally resides in soils are well known for performing a wide range of functions that are essential to sustain soil health. For example, soil micro-organisms decompose organic matter, release nutrients into plant-available forms, and degrade toxic residues. They also form symbiotic associations with roots (facilitating nitrogen fixation or phosphate uptake), act as antagonists to pathogens, influence the weathering and solubilisation of soil minerals, and contribute to the maintenance of soil structure. Larger soil organisms, such as earthworms, contribute to soil health through mixing and decomposing organic residues within the soil and forming biopores.
However, root disease pathogens, have detrimental effects reducing plant productivity and hence the efficient use of nutrients and water in the soil. There are well documented examples of the major effects of the root pruning disease, Rhizoctonia, on wheat yield and nutrient uptake. It has also been shown that the disease left large quantities of unused water and nitrate within the soil profile at harvest. Such effects may respectively accelerate regolith water recharge and lead to groundwater contamination.
Various agricultural practices directly and indirectly influence the maintenance of soil biological health. For example, building up organic matter through conservation tillage or under green cane harvesting directly and indirectly conserves the organ material in the soil - hence maintaining soil as a store of nutrients and water. There are no national soil biology or biological health data sets for Australia - surrogates often used include organic carbon content and carbon to nitrogen ratios.
Soil organic matter - a key biological property
Soil organic matter in soil is a key property, having essential functions in the physical, chemical and biological health of soils. The property confers a capacity to buffer against and resist impacts induced by changed soil conditions. It thus provides vital resilience to soil health.
Organic matter reserves of soils vary appreciably between soil types and topsoils are more enriched than subsoils. The reserves reflect the balance between carbon (C) inputs from plant growth (C capture through photosynthesis)and C losses caused by soil microbial respiration and high removal of C in harvested products.
In natural ecosystems, soil organic matter tend towards a unique equilibrium value, determined by the balance between C inputs and losses. Generally, the values obtained reflect climatic conditions of the ecosystem: rainfall affecting the C inputs from photosynthesis, and temperature affecting both the rate of C inputs (via plant biomass) and C losses (via microbial respiration).
When soils are developed for agriculture and cultivated, the natural equilibrium state is disturbed, and large C losses initially occur. These losses can be further and progressively exacerbated by frequent soil cultivations (eg. conventionally tilled long fallows), but downward trends can be partially reversed by pasture phases (where C gains exceed C losses) and by reduced tillage.
Therefore soil organic matter reserves in agricultural soils attain new, long-term, equilibrium status dictated by climate and soil management practices. Along the way, annual fluctuations in C fluxes contribute to the level reached and rate at which the new equilibrium C is reached by affecting net C balance. The new status achieved affects the capacity of each soil to respond to changed soil conditions, through the combined impact that soil organic matter has on the physical, chemical and biological functions and soil processes.
Soil classification
Soil classification serves as a framework for organising our knowledge of Australian soils and provides a means of communication among scientists, and between scientists and those who use the land. Commonly used classification schemes in Australia include:
- the Australian Soil Classification (ASC), the current preferred standard
- Great Soil Groups
- the Northcote Factual Key
- standard soil descriptions used within state agencies, for example Western Australian Soil Groups and South Australian Soil Groups
- local soil names.
Click here for more information on soil classification.
Atlas of Australian Soils
The Atlas of Australian Soils (Northcote et al, 1960-68) was compiled by CSIRO in the 1960?s to provide a consistent national description of Australia?s soils. It comprises a series of ten maps and associated explanatory notes, compiled by K.H. Northcote and others. The maps are published at a scale of 1:2,000,000, but the original compilation was at scales from 1:250,000 to 1:500,000.
Mapped units in the Atlas are soil landscapes, usually comprising a number of soil types. The explanatory notes include descriptions of soils landscapes and component soils. Soil classification for the Atlas is based on the Factual Key.
A generalised map of the soils of Australia using the principal profile form (Factual key) based on the Atlas of Australian Soils is shown below.
Digital Atlas of Australian Soils
In 1991, a digital version of the Atlas was created by the Bureau of Rural Science from scanned tracings of the published hardcopy maps. The Digital Atlas of Australian Soils is available as an ARC/INFO coverage. The lookup table provided with the Digital Atlas only gives one (dominant) soil type for each landscape.
Three lookup tables are currently available on the BRS web site for the Digital Atlas of Australian Soils (the 'Digital Atlas'). They are:
- Soil properties that affect land management
- Interpreted typical land use
- Interpreted A1 horizon organic content
These lookup tables provide additional interpreted attributes for each map unit in the Digital Atlas. Since the soil type in each soil landscape is somewhat variable, the lookup tables should be used cautiously.
For more information, see the BRS web site
Associated soils in the mapped units can be as important as the dominant soil, or more so, depending on the application. For Australian Soil Resources Information System , an additional lookup table was used. This table, compiled by Leahy (1993), lists all soil types identified in each map-unit, and their relative proportions within the unit. This allowed estimates of soil properties for the unit to be based on all soil types within the unit, rather than just the dominant soil type (see Australian Soil Resources Information System section for details).
Interpretative tables of soil properties for the Atlas of Australian Soils
McKenzie et al (2000) compiled tables estimating typical ranges for soil properties associated with each principal profile form (PPF) of the Factual Key. These tables were intended for use with the Atlas of Australian Soils, to provide estimates of specific soil properties for each map-unit.
Interpretations for each soil type were based on the range observed in approximately 7000 soil profiles held within the CSIRO National Soil Database, with ancillary data from Northcote et al. (1975). The systematic structure of the Factual Key makes interpolation between soil classes relatively straightforward. Soil properties were estimated using a simple two-layer model of the soil consisting of an A and B horizon. The following properties have been estimated for both the A and B horizon: horizon thickness, texture, clay content, bulk density, grade of pedality and saturated hydraulic conductivity. The estimates of thickness, texture, bulk density and pedality have been used to estimate parameters that describe the soil water retention curve - these allow calculation of the available water capacity for each layer. Interpretations relating to the complete soil profile are presence or absence of calcrete and gross nutrient status.
Caveats on the use of these interpretative tables to predict soil properties spatially are discussed by McKenzie et al (2000). A very large proportion of soil variation within a region occurs over short distances and cannot be resolved by reconnaissance scale maps. The qualitative nature of the Atlas and restrictions associated with the classification scheme and structure of the soil-landscape model impose further constraints.
McKenzie et al (2000) were not able to provide estimates for all soil properties for all PPFs. Carlile et al (2001) added some additional attribute values to the look-up tables based on data from the ASRIS point database.
These interpretative tables were used in ASRIS to provide estimates of soil properties for polygon based modelled surfaces of soil properties.
technical document describing the development of the database and models.(PDF 9.1 MB)
Further Information
- Exit to more information on the Australian Soil Classification from the Australian Collaborative Land Evaluation Program website.
- Exit to download the Digital Atlas of Australian Soils
- technical document detailing the development of soil property prediction using soil maps (PDF 9.1 MB)
- technical document detailing estimation of particle size distribution (PDF 1.3 MB)
- spreadsheet detailing laboratory methods used and number of samples (MS Excel 86 KB)
- table detailing land use classes used in Australian Soil Resources Information System modelling (MS Word 32 KB)
- statement on data quality for South Australian data (MS Word 24 KB)
- statement on data quality for Western Australia data (MS Word 24 KB)
Proposed Polygon Standards
- technical document detailing the polygon data standard for land resource data sets (MS Word 77 KB)
- technical document detailing the polygon attributes proposed as part of the polygon standard for land resource data sets (MS Word 24 KB)
References
The Australian Soil and Land Survey Handbook Series provides guidelines to promote consistent methods and standards for soil and land resource surveys and analysis in Australia. The series includes:
- Australian Soil and Land Survey Field Handbook (The Yellow Book): specifies methods, standards and terminology for the description of sites in the field.
- Australian Soil and Land Survey Handbook - Guidelines for Conducting Surveys (The Blue Book): provides guidelines to promote the development and implementation of consistent methods and standards for conducting soil and land resource surveys in Australia.
- Australian Soil and Land Survey Handbook - Australian Laboratory Handbook of Soil and Water Chemical Methods (The Green Book): promotes standardisation of soil and water analysis, and provides guidance on the choice and application of analytical methods, field sampling and the pre-treatment and preservation of samples.
- Soil Physics Handbook: due to be published in 2001, it will provide descriptions for soil physical measurements and guidelines on the interpretation of results and integration with land resource assessment.
For more information (references below) visit the Australian Collaborative Land Evaluation Program website at http://www.clw.csiro.au/aclep/
Further reading
ACLEP (1997): Soil Information Transfer and Evaluation System: Version 1.2. ACLEP Technical Report No.5
AUSLIG (1997) Australia?s river basins. metadata hosted by Geoscience Australia
BRS (2000) Digital Atlas of Australian Soils
Cresswell, H. P., McKenzie, N. J. and Paydar, Z. (1999). Strategy for determination of hydraulic properties of Australian soil using direct measurement and pedotransfer functions. In "Characterization and Measurement of the Hydraulic Properties of Unsaturated Porous Media." (Eds. M. Th. Van Genuchten, F. J. Leij and L. Wu). (University of California, Riverside).
Bui, EN, Moran, CJ and Simon, DAP (1998) New geotechnical maps for the Murray-Darling Basin. CSIRO Land and Water Technical Report 42/98. http://www.clw.csiro.au/publications/technical
Gunn, RH, JA Beattie, RE Reid, RHM van de Graff (eds) (1988) Australian Soil and Land Survey Handbook: Guidelines for Conducting Surveys. Inkata Press, Melbourne.
Hall, J.A., Maschmedt, D.J., Billing, N.B., Cichon, C.S. and Sandland, A. (in prep) Soils of South Australia?s Agricultural Districts. PIRSA, Adelaide.
Henderson, B, Bui, E, Moran, C and Johnston, R (2001) Continental-scale soil property modelling from a national soils database. Abstract submitted to Pedometrics 2001.
Isbell, R. F. (1996). The Australian Soil Classification. CSIRO Publishing, Melbourne.
Isbell, R.F., McDonald, W.S., Ashton, L.J (1997) Concepts and rationale of the Australian Soil Classification. ACLEP, CSIRO Land and Water, Canberra
Jacquier, DW, McKenzie, NJ, Brown, KL, Isbell, RF and Paine, TA (2000) The Australian Soil Classification - an Interactive Key. CSIRO Publishing. (CD-ROM).
Leahy, S. (1993). Atlas of Australian Soils: Map Units and Component Soils. National Resources Information Centre, Parkes, ACT.
Maher, JM and Martin, JJ (1987) Soils and Landforms of south-western Victoria. Research Report No. 40. Victorian Department of Agriculture and Rural Affairs.
McDonald, RC. Isbell, R.F., Speight, J.G. Walker, J. Hopkins, M.S. 1990: Australian Soil and Land Survey - Field handbook Second edition. Inkata Press, Melbourne
McKenzie, N.J., Jacquier, D.W., Ashton L.J. and Cresswell, H.P. (2000) Estimation of Soil Properties Using the Atlas of Australian Soils. CSIRO Land and Water Technical Report 11/00.
McKenzie, N. J. and Hook, J. (1992). Interpretations of the Atlas of Australian Soils. Consulting Report to the Environmental Resources Information Network (ERIN). CSIRO Division of Soils Technical Report 94/1992.
Northcote, K. H. with Beckmann, G. G., Bettenay, E., Churchward, H. M., Van Dijk, D. C., Dimmock, G. M., Hubble, G. D., Isbell, R. F., McArthur, W. M., Murtha, G. G., Nicolls, K. D., Paton, T. R., Thompson, C. H., Webb, A. A. and Wright, M. J. (1960-1968). Atlas of Australian Soils, Sheets 1 to 10. With explanatory data (CSIRO Aust. and Melbourne University Press: Melbourne).
Northcote, K. H., Hubble, G. D., Isbell, R. F., Thompson, C. H. and Bettenay, E. (1975). A Description of Australian Soils. (CSIRO: Melbourne).
Northcote, K.H. (1979) A Factual Key for the Recognition of Australian Soils. 4th edn., Rellim Technical Publishers, Glenside, SA.
NSW DLWC (1999a) Soil and Regolith Attributes for CRA/RFA Model Resolution (Upper North-east and Lower North-east CRA Regions). Dept of Urban Affairs and Planning, Sydney.
NSW DLWC (1999b) Soil and Regolith Attributes for CRA/RFA Model Resolution (Southern Regions). Dept of Urban Affairs and Planning, Sydney.
NLWRA (2001) Australian Agricultural Assessment 2001. Draft Final Report, Agricultural Productivity and Sustainability. National Land and Water Resources Audit. Canberra.
Peverill, KI, Sparrow, LA and Reuter, DJ (1999) Soil Analysis: an interpretation manual 369 pp. CSIRO Publishing, Melbourne.
Rayment, GE and FR Higginson (1992) Australian Soil and Land Survey Handbook - Austrlian Laboratory Handbook of Soil and Water Chemical Methods. Inkata Press, Melbourne.
Rowan, J. (1990) Land Systems of Victoria (Version 2). Land Conservation Council of Victoria.
Schoknecht, N.R. (2001) Soil Groups of Western Australia. A guide to the main soils of Western Australia. Resource Management Technical Report No.193, Second edition. Agriculture Western Australia
Stace, HCT, Hubble, GD, Brewer, R, Northcote, KH, Sleeman. JR, Mulcahy, MJ and Hallsworth, EG (1968) A Handbook of Australian Soils. Rellim Technical Publishers, Glenside, SA.
Walker, PJ (1991) Land Systems of Western New South Wales. Soil Conservation Service of NSW Technical Report No. 25.
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