12EES - Review of soils of Australia

Review of the soils of Australia.

In the first week of our new class format everyone should have completed the following:

1.  The survey
2.  The question sheets
3.  The "dot point" questions/summaries.


The key points to be aware of are as follows:

1.  Age
Western Australian soils come from rocks that are very old (over 2 billion years).  Over time the minerals form the soil get leached from it by rainfall (the minerals that are dissolvable/soluble in water are removed and sink further away from access by plants).  Eastern Australian soils have been formed from rocks that are only 10,000 to 30 million years old.  Because of this they are far richer in minerals, and unsurprisingly make some of the most productive soils in this country.  The reason the rock/soil in Eastern Australia is so young by comparison is due to the eastern region of Australia drifting over a hot spot which in turn led to a chain of volcanoes forming from QLD down to southern Victoria.

2.  Rainfall.
Easter Australia is far wetter than most of Central Australia and WA.  As a result vegetation is reduced.  Vegetation is required to contribute to the organic content of the soil.  In addition moist soil contains more micro-organisms which help break down the dead material into materials that can be absorbed by the soils and therefore accessible to plants planted by farmers.

3. Topography
You would notice that in the presented maps, that the only significant an rapid changes of height above sea level are on the Eastern coast.  This means that when moist air is pushed up over these areas the moisture is more likely to condense and fall as rain.  In Western Australia, the air passes over mostly flat terrain and so has less opportunity to form clouds and rain.  The consequences of this is reduced rainfall (See 2.)

4. Lack of Glaciation
In recent history Australia has had no significant glaciation over the continent.  When the last ice age ended 10000 years ago, the glaciers in Europe and North America had scoured away the old soils and replaced them with new ones made from the freshly ground rock that the glaciers had passed over.  Because these soils are much newer they have a much greater mineral content compared to most Australian soils.


Differences between Easter and Western soils.

Eastern soils - red to brown due to higher mineral and organic content.  Generally high in nitrates and phosphates.  Some trace elements such as magnesium may be a bit low, but the soils are suitable for agriculture without the need for large scale fertiliser addition.

Western soils - Yellow to red soils with high silica content.  This is a result of prolonged leaching causing minerals that are useful to plants being leached out.  These soils tend to be low in nitrate and phosphate and for successful farming, repeated applications of fertiliser may be required.