Soil: more than just dirt

What do the following have in common: writing, driving a car, eating, playing football, and playing a guitar? It may not be obvious, but they all rely directly or indirectly on soil. People need to look after soil; although it is formed continually, the rate of formation is very slow, making soil a non-renewable resource in practical terms.

Related Activities: Looking at your soil

The making of soil

Soil formation is a slow process. A centimetre of soil may take hundreds of years to form. Australian soils are generally very old. Some are 100 million years. Over this immensely long time period, these soils have been changed dramatically. Rain has leached them for so long that most of the nutrients have disappeared. Some trace elements may have disappeared altogether.

A feature of much of the Western Australian landscape is that the surface soil has been removed and deposited over a long period of time. A patchwork of soil types occurs in Western Australia. This can be demonstrated by the fact that many farmers may have three or four soil types in a single paddock.

This soils map of South Western Australia will confirm this.

Related Activities: Weathering - a force to be reckoned with

What is soil?

To some people soil is little more than dirt. It is, however, a very complex substance. The small bits of broken rock are mixed with organic matter, and organic matter plays a very important role in keeping the soil together. The humus part of organic matter acts as glue, cementing the rock particles together to form lumps called aggregates. The aggregates give soil an open, crumbly structure that is easy for plant roots to penetrate and ideal for letting in water and air. Because of their size and structure, aggregates make the soil resistant to wind and water erosion.

Soil is alive

If you were to investigate soil under a microscope, you would be amazed at the amount of life it contains. A whole ecosystem exists in soil, with plants being the source of bio-mass.

Due to the arid climate, the soil animals are widely dispersed in most Australian soils. In rich moist soils or compost, you would find that mites dominate the ecosystem, followed by springtails and millipedes. These animals enhance decomposition by breaking up the organic matter and making it more palatable and digestible for bacteria and fungi. Termites are the earthworms of tropical soils. The soil plant and animals are important to us because they keep soil in top condition. Disturbances, such as cultivation or the addition of extra nutrients, change the balance of the ecosystem, usually to the detriment of soil and its structure. Animals in the soil ecosystem are sensitive to chemicals and cultivation. Any change in the diversity of the soil is reflected in the plants and animals, which is one of the first things to suffer in land degradation.

Related Activities: How does soil form? - How does soil structure influence plant growth?


Soil influences the environment

Soils have a major influence on the organisms that live in an area. A fertile soil will allow a greater number of plants and animals to grow than an infertile soil. However, Western Australian plants and animals are well adapted to our mostly infertile soil types. Relationships between plants and animals and other micro-organisms are quite common allowing them to cope with lack of nutrients.

Soil types can often be recognised in landscapes by the vegetation they support. Brown loam soils in the wheatbelt usually support morrel or Eucalyptus longicornis and is often called 'morrel soil'. Deep loam soil in the South West supports Eucalyptus diversicolor and is named 'Karri loam'. On the Swan coastal plains, 'Banksia sands' are deep grey sandy soils on which Banksia spp. dominate.

Related Activities: Classifying Soils

Soil - who needs it?

No organism can survive without living things. There are many links among plants, animals and their environment. You can probably list a few of the ways in which you depend on other organisms - for example, other people. One way in which all organisms are linked to their environment is by the soil.
Soil is a vital part of your environment; just think how many things we take for granted that come directly or indirectly from the soil:

most of the food we eat comes from the soil;
the fibres we use to make clothes often comes from plants (for example, cotton) or animals (for example, wool) and soil is needed to produce the fibres;
many building materials come from the soil, for example, timber, bricks and minerals; and
much of our drinking water is pumped from the soil.
People, however, are not the only organisms that need soil. Soil has a mojor influence on all animals and plants of a region. Plants rely directly on soil for minerals and water. The more water soil can hold and the longer it can hold this water, the longer plants can keep growing. Such a soil will support more plants than one that dries out quickly.

Soil plays a part in many of nature's cycles. An important stage of the water cycle involves the soil. Rainfall may penetrate the soil and end up as groundwater and or artesian water.

The mineral cycle also relies heavily on the soil. Millions of tiny soil organisms, the decomposers, work to break down the remains and wastes of plants and animals and return minerals back to the soil.

Larger animals, such as earthworms, ants and termites, do their bit too. They chew and break up the organic materials and this makes it easier for bacteria and fungi to complete their decomposing work. Without these soil organisms, minerals would not be returned as plant food and finite resources would soon run out.

Soil can be a great place to live:70 000 organisms per cubic metre of Swan coastal plain topsoil cannot be wrong. Many animals, such as ants, termites and earthworms, make soil their permanent home. In fact, some peoplehave started to copy these animals; in certain parts of Australia, houses are partly buried in soil. This keeps them cool in summer and warm in winter and also gives excellent protection against bushfire hazards.

Soil is not dirt; it is vital part of your environment. It needs our care and attention, for without healthy soil, we cannot survive. Soil - who needs it? In fact, we all do!

Related Activities: Soil - who needs it?

Next » | « Back to Index