Everyone wants clean air. We recycle to save energy and worry about pollution in the water supply. We fear the ever rising global thermostat. But one fragile and fundamental piece of the environment is prone to invisibility. Here’s a hint: You’re stepping on it!!
Soil is as precious a resource as any, and it should be protected as such. Soil is an astonishing material that mantles most of the earth’s solid surface. It is formed by rock and mineral weathering, by transport in wind and water, and by biological activity.
Soil has some remarkable properties. Soil has an amazing surface area - 1 kg of soil can have a surface area of its particles of over 75 ha. This large surface area carries a huge amount of mostly negative electrical charges which create a natural reactor source in the landscape that performs many vital functions in living processes.
Soil stores rainfall - it provides a buffer that ensures that streams and rivers flow long after storms have ceased. In the process, water is filtered and purified. Soil also supplies water and nutrients to plants. This involves myriad processes fundamental to the production of food and fibre from agriculture.
Most importantly, soil is essential for the maintenance of biodiversity above and below ground. The wealth of biodiversity below ground is vast and often unappreciated: millions of microorganisms live and reproduce in a few grams of topsoil, an ecosystem essential for life on earth because it is critical for the cycling of carbon and oxygen.
If you doubt the value of dirt, consider history, and explanations of why, and how, civilizations fall. Societies are forged on soil, and often die when it does. You can cite Easter Island, the Fertile Crescent of the Middle East and the Mayans of pre-Columbian Mexico and Guatemala as examples of once-thriving societies that collapsed when their soils were spent.
Soil problems are rarely front page news, according to Jared Diamond the University of California geographer and author of Guns, Germs and Steel, because they are not spectacular. But they result in a steady decline in agricultural productivity, and serious environmental effects beyond the farm.
Damaged soil is an obvious loss for agriculture but it can also spoil the surrounding air and water. For instance, heavily eroded soil leaches pollutants into groundwater.
Most Australians live in urban areas and have limited direct contact with soil beyond occasional gardening. They largely fail to appreciate that in most parts of Australia, soils and landforms have evolved over extremely long periods of time.
Most soils have taken tens to hundreds of thousands of years to develop, and in some landscapes the soil cover may have lain in place for millions of years. The predominantly harsh landscapes of the continent have shaped life for hundreds of generations of Australians and we are beginning to learn that humans have, in turn, dramatically changed the natural environment.
The extent of the impact on soils of the initial Aboriginal colonisation of Australia some 60 000 years ago coincides with major changes in fire, vegetation and wildlife. More dramatic has been the short period of European settlement. While many European settlers had a good eye for the agricultural potential of land, most underestimated the capricious climate and failed to understand limitations inherent to the often old and impoverished soils.
Australians have generally learned the hard lesson of how to adapt to the often erratic annual and longer-term variations in climate. However, they don’t always have a similar appreciation of how soil affects land use, essential for developing forms of land use that can support them in perpetuity.
Protecting and enhancing our soil is an enormous challenge, particularly in landscapes where humans have already dramatically altered the natural order. In one sense the principles are simple - maintain organic matter, prevent compaction and ensure the soil is not too acid or alkaline.
But implementing these principles across vast tracts of land, where rainfall is usually unpredictable and in short supply, is much harder. Add to this the great variety of soils with their many peculiar properties and the challenge is magnified.
The quality of land management over large parts of Australia has improved in recent decades, but there are still unsustainable rates of soil erosion, widespread acidification, low organic matter levels, and salinity as major problems for many communities. Overcoming these problems requires a combined effort from individuals, communities, government and industry. An important element is improved land literacy.
We need to understand the suitability of land for particular uses and learn ways of lifting constraints to plant growth. An appreciation of the fundamental properties of soil, along with knowledge of its diversity and distribution, is an essential part of all this.
It is essential to appreciate the basic physical, chemical and biological properties of soils if you want to understand the mechanisms of how soils are formed, the relationships of soils with landscape processes and the likely outcomes of different land management strategies for your land.
Most people regard soil as being the top 20 cm or so of “earth” that they cultivate before growing their crops or pastures. However, to a soil scientist the complete soil includes the topsoil and all the subsoil layers down below this to the mineral rock material or parent material from which the soil has developed.
Soil varies both vertically and horizontally in the landscape. The main focus of soil mapping is often on the vertical variation (known as the soil profile) as the horizontal variability (known as the Soil Continuum) is more continuously variable, as its name suggests, and often harder to map accurately. The key is to think of your soils in three dimensions, to try and understand how soil properties and soil profiles vary across the landscape.
Characteristic and predictable horizontal sequences of soils are found in most contrasting landscapes. These sequences of soils are referred to by various names including catenas, toposequences and soil landscapes and form the basis for mapping soils.
