The State of Australia’s Soils

30 April 2015 FDI Team

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Christopher Johns
Research Assistant
Northern Australia Research Programme

 

Key Points

  • Australian soils differ from those of northern America or Europe, where much scientific study on soil regeneration is taking place. Australian soils are generally older and have been exposed to constant weathering.
  • Knowledge of the importance of soils and soil science is seen to be declining.
  • Soils play an important role in three of the key debates of our time: food security, water quality and climate change.
  • Soil degradation is the decline in soil quality caused by its improper use, usually for agricultural, pastoral, industrial or urban purposes. This is a serious global problem and is being exacerbated by climate change.
  • A significant proportion of the cropland and improved pasture in Australia is affected by some form of soil degradation.

     

Summary

A detailed knowledge of the state of Australian soils is currently difficult, if not impossible, to ascertain. The vast size of the country, climatic variation, the complexity of measurement and cost are just some of the reasons why the task is prohibitive. This situation notwithstanding, it is vital we develop such knowledge so as to inform key policy and decision makers of the state of our soils and what needs to be done to address the continued decline in their fertility. Soil has fundamentally important role in three of the key debates of our time: food security, water quality and climate change. There are a number of degraded soil conditions currently causing environmental and economic concern in Australia: acidification, erosion, salinity, depletion, structural decline and compaction are just some of them.

 

Analysis

In March 2014, the Minister for Agriculture, the Hon. Barnaby Joyce, released the National Soil Research Development and Extension Strategy. This Strategy, combined with the extended appointment of Major General the Hon. Michael Jeffery as the National Advocate for Soil Health and the leadership, coordination, direction and advocacy provided by the National Committee for Soils and Terrain, for the first time provides Australia with a national, coordinated and forward thinking approach to managing our soil. One of the most important and challenging tasks they face is the provision of an accurate and current assessment of the state of Australian soils.

Soils are complex and Australian soils differ from those of northern America or Europe where much scientific study on soil regeneration is taking place.  Australian soils are generally older and have been exposed to constant weathering.  Unlike Northern Hemisphere soils, which have been farmed for centuries, Australian soils have only been cultivated since British settlement and, as a result, have been exposed to influences widely different from those under which they were formed.

Within Australia soils also differ widely. Spread over 7,692,024 square kilometres, approximately one-third lies in the tropics. Soil types vary from alpine regions in parts of south-eastern Australia and Tasmania, through the Mediterranean zones of southern and south-western Australia to the wet and dry tropics of Queensland and very low rainfall areas of the centre. Indeed, over one million square kilometres of the Northern Territory and the northern part of Western Australia are almost devoid of soil and what exists is usually shallow, leached and mildly acidic. This diversity adds to the complexity of analysing soils and determining what needs to be done to regenerate them.

To compound these problems, knowledge of the importance of soils and soil science is also seen to be declining.  The gradual contraction and demise of soil conservation surveys, or their equivalent have, resulted in the loss of a generation’s worth of knowledge.  Even the teaching of soil related sciences, in our tertiary institutions, has declined. Government agencies are decreasing their involvement in soil research, and communication of soils-related knowledge to land managers and the community is declining.  Instead, consultants are hired to answer a specific problem resulting in piecemeal solutions which are not shared throughout the agricultural community.

The National Soil Research Development and Extension Strategy and other recent, soil related initiatives, acknowledge the important role soils play in three of the key debates of our time: food security, water quality and climate change. Along with air and water, soil is one of the essentials of life and among our most basic natural resources. It supports the overwhelming majority of our terrestrial biodiversity and it contains vast quantities of carbon and water. It plays a fundamental role in the water and carbon cycles as well as being the engine room for food production. As a recent publication from the Federal Government Department of Agriculture stated, healthy soils grow healthy foods, which grow healthy rural and urban communities.

In the public domain, opinion on the state of Australian soils is diverse and, at times, polarised. The first national audit of Australian soils in 2000 found they were declining due to processes such as erosion, acidification and salinisation. A second national audit in 2008 concluded that soils need long term monitoring, consistent information and a data baseline in order to monitor changes. In the report, Australia: State of the Environment 2011, the Federal Government Department of Environment found that in general, soils are ‘in good shape’. There is a warning, however, that there are adverse trends and degradation of soil is environmentally and economically significant in many areas. The WA Department of Agriculture and Food and the NSW Department of Primary Industries, in particular, highlight areas of significant concern.

Soil degradation is the decline in soil quality caused by its improper use, usually for agricultural, pastoral, industrial or urban purposes. This is a serious global problem and is being exacerbated by climate change. Examples of soil degradation include the loss of organic matter, decline in soil fertility and its structural condition, wind and water erosion, adverse changes in salinity, acidity or alkalinity and the effects of toxic chemicals and pollutants. A significant portion of the cropland and improved pasture in Australia is affected by some form of soil degradation. Australian soils, therefore, are in trouble. Not only are they degrading more quickly than they can be regenerated, but there is also a sense that Australian land managers are losing the capacity to even know what state they are in.

In general, soil productivity is largely determined by moisture absorption and retention which can vary greatly depending upon soil types and the timing of the rainfall. On only about 10 per cent of the continent is rainfall sufficient for plant growth for more than nine months of the year.  On the other hand, low and unreliable rainfall over the greater part of Australia results in no arable agriculture or sown pasture production. As a result limited pastoral activities are the most likely outcome. In some areas, particularly in New South Wales and Western Australia, the degradation of once productive soils is limiting productivity further.

The following is a description of just some, though certainly not all, of the key forms of soil degradation experienced by Australian agricultural soils.

Acidification

The acidity and alkalinity of soil is expressed using the chemical term pH where, on a scale of 0 to 14, less than seven represents acidity, seven neutrality (such as distilled water), and more than seven, alkalinity. Soils acidify naturally as they weather over millions of years. The acidity of any soil varies according to the type of rock it comes from, the length of time it has weathered, the native vegetation and the local climate. As a result, some soils can be naturally very acidic (low pH) while others are much more alkaline (high pH).

Agricultural production systems can increase the rate of soil acidification and it has become an environmental and economic concern in parts of the country. Approximately 50 per cent of Australian agricultural land has surface pH values less than or equal to 5.5, which is below the optimal level to prevent soil acidification. If untreated, acidity will become a problem in the subsurface soils, which are more difficult and expensive to treat. Subsurface acidity is already a major problem for large areas of Western Australia and New South Wales. It is estimated that 12 to 24 million ha are highly acidic with pH values less than or equal to 4.8.

Acidic soils cause significant losses in production. Where the choice of crops is restricted to acid tolerant species and varieties, profitable market opportunities may be reduced. In pastures grown on acidic soils, production will be reduced and some legume species may fail. Deep-rooted species, such as native trees, required to increase water usage may not thrive, increasing the risk of salinity. Increased run-off and subsequent erosion has detrimental impacts on streams and water quality. Increased nutrient leaching may pollute ground water.

The Federal Department of the Environment in its publication, Australia State of the Environment 2011, found that a deteriorating trend in soil acidity was being experienced in almost every agricultural region in the nation.

Erosion

Erosion is defined as the removal, by wind and water, of the upper layers of soil. When it occurs at a faster rate than the soil forming processes, it leads to a loss of topsoil, organic matter and nutrients. This leads to a loss in fertility. When unchecked it can lead to both desertification and the removal of topsoil through flooding.