About Soil

Soils are a vital part of the natural environment

They are very complex, with different types occuring across Australia. The different properties of soils influence the types of plants and animals that thrive on them, and the ways in which we may use them.

State Soils

Our branches each selected a State Soil - similar to having a State animal and flower

New South WalesRed Chromosol
Northern TerritoryKandosol
QueenslandVertosol
South AustraliaCalcarosol
TasmaniaFerrosol
VictoriaMottled Brown Sodosol
Western AustraliaYellow Chromosol

Soil contains amazing species diversity

A teaspoon of soil is estimated to contain several thousand species of micro-organisms, and other invertebrates such as nematodes (round worms), annelids (earth worms), and microarthropods (springtails and mites). One square metre of soil can contain more species in it than a square kilometre of rainforest. These soil organisms play very important roles such as breaking down organic matter and providing nutrients to plants.

Clay is kind of phenomenal

Cracking clays (Smectites) crack when they dry and swell when they are wet. They can expand/contract as much as 30% during wetting and drying, which can be devastating for road and building foundations, but highly important for agricultural production.

One teaspoon of a cracking clay soil has the surface area of a football field, whereas one teaspoon of a rigid clay (kaolinite) has a surface area of only 10 to 20m².

Sporting soils

Soil science is integral to developing sporting fields and golf courses that are playable in our variable climatic conditions.

Swelling and shrinking are very important properties for cricket wickets. These properties allow the typical black cracking clays to restructure after compaction.

For example, the Adelaide Oval pitch, widely regarded as the best in the world, is made of Athelstone soil, a black cracking clay. The soil has been used since the first Test Match was played at Adelaide Oval in 1884 and legendary retired curator Les Burdett said it’s still the soil of choice, 126 years on:

From that day forward, from the history I’ve researched, it’s always come from there. In Sydney they have Bulli soil from an area called Bulli, in Melbourne they have Mary Creek soil from Mary Creek ... and in Adelaide we have Athelstone soil from Athelstone”. (see source article in the Adelaide Advertisor)

Soils and Greenhouse gases

Organic carbon (C), present in soil organic matter, is an important global carbon pool, estimated to be 1550 Gt (1 gigatonne = 100 million tonnes). The soil organic C pool (to a depth of 1 m) is approximately three times larger than the amount of C stored in vegetation and twice the amount stored in the atmosphere [1] . 

Mainly because of our dry climate, organic C stocks in Australian soils are much lower than the global average, and are estimated to be about 50 Gt [2].

Soil cultivation and soil degradation result in losses of organic carbon which is released as carbon dioxide into the atmosphere. 

Agricultural soils, mainly through the use of nitrogen fertilisers, are also significant emitters of nitrous oxide, a greenhouse gas more potent than carbon dioxide. 

Emissions of greenhouse gas from Australian agricultural soils accounted for 19 million tonnes of carbon dioxide equivalents in 2003, or about 3% of the national greenhouse gas total emissions for that year [3].

Land clearing and overgrazing also contribute to the loss of soil carbon.

Improved soil management strategies such as revegetation, conservation cropping and reducing grazing pressure have the potential to increase the store of soil C, thereby acting as sinks for atmospheric C.

Issues affecting soils and management costs

Safeguarding the health of our soils is vital to Australia's future, from environmental, social and economic perspectives. There are many issues that affect our soils and landscapes including salinity, acidity, compaction, erosion, fertility decline and loss of biodiversity.

Managing soils appropriately is very important as the costs from degraded soils and their management can be very high and affect agricultural producers, commerce and industry, urban users, and the natural ecosystem.

Costs to the community associated with soil salinisation in Australia are very large, estimated to be in excess of $300 million dollars per year in the Murray-Darling Basin alone [4]. Salinisation occurs when the water table rises, bringing natural salts to the soil surface which can accumulate and become toxic to most plants. A primary cause of surface soil salinisation in Australia has been extensive land clearing, predominantly for agricultural purposes. This has allowed saline groundwater tables to rise, bring salt closer to the surface. In the early 2000s, 5.7 million hectares of Australia were assessed as having a high potential to develop salinity with 20,000 farms and 2 million hectares of agricultural land showed actual signs of salinity [5]. Predictions indicate that unless effective solutions are implemented, the area affected could increase to 17 million hectares by 2050, 64% of which is agricultural land. 

Soil acidity affects approximately 50 million hectares (50 per cent of Australia’s agricultural land) and about 23 million hectares of subsoil layers, mostly in Western Australia and New South Wales [6]. Soil acidification restricts options for land management, because it limits the choice of crops and vegetation to acid-tolerant species and varieties. It is relatively straightforward to reverse short-term surface soil acidification through the application of lime. However, it is much harder to reverse the problem if the acidification has advanced deeper into the soil profile, because incorporating lime at depth is more expensive.

Drainage and excavation of land, diversion of water, and climatic effects, has also resulted in exposure of acid sulfate soils in coastal and inland areas around Australia. The pyrite (sulfidic material) in these soils can oxidise to from sulfuric materials, producing severe soil acidification (pH<4). The acidity can leach to surrounding waterways, results in severe ecological and other effects. The cost for management of acid sulfate soils in Queensland is estimated at >$100 million dollars per year [7]. 

[1] Lal, R (2004). Soil carbon sequestration impacts on global change and food security. Science 304 1623-1627.

[2] Jan Skjemstad, CSIRO Land and Water, Adelaide.

[3] AGO, National Greenhouse Gas Inventory (2003). 

[4] Wilson, SM (2004). Dryland and urban salinity costs across the Murray-Darling Basin. An overview & guidelines for identifying and valuing the impacts, Murray-Darling Basin Commission, Canberra.

[5] Australian Bureau of Statistics (2010). 1370.0 - Measures of Australia's Progress.

[6] Soil: Salinity and acidification - Land (2016 State of the Environment Report)

[7] see Ozcoasts website report