The principal pressures on the environmental values of land under conservation, land not formally protected but subject to minimal use, and land formally owned and managed by Indigenous Australians are the continental, regional and landscape-scale factors discussed in Section 3.3.2—grazing by pest animals, and grazing by domestic livestock on those tenures where it is allowed. These pressures have been comprehensively reviewed by the Assessment of Australia’s terrestrial biodiversity 200846 and, for the rangelands where much of the minimal use and Indigenous lands are located, by Bastin et al41
The major impacts of agriculture relating to carbon, acidification and erosion were considered in Section 2.2. Here, we also consider those impacts relating to soil nutrients, cultivation and compaction.
The nutrient balance of Australian landscapes (i.e. net gains and losses of nitrogen, phosphorus, sulfur, potassium and other essential nutrients) depends on the system of land use. As a generalisation, the most sustainable systems of land use tightly cycle nutrients, with limited leakage to the atmosphere, streams and groundwater. The NLWRA42 provides an extensive summary of nutrient balances across Australia.
Careful nutrient management is an important determinant of profitability and sustainability in agriculture and forestry. The environmental aspects of nutrient management of greatest relevance to this report occur when:
- nutrient leakage to the atmosphere contributes to GHGs
- nutrient leakage to inland waters, estuaries and coastal waters results in eutrophication and adverse environmental impacts
- nutrient availability decreases (e.g. due to insufficient nutrient inputs or acidification) and options for future land use are lost
- nutrient availability constrains net primary productivity and limits carbon sequestration in soils.
The environmental impact of leakage from soils to inland waters and estuaries is considered in Chapter 4: Inland water, and emission of GHGs from the land sector is summarised in Chapter 3: Atmosphere. The degree to which nutrient availability constrains agriculture and forestry is closely monitored by organisations involved in primary industries (e.g. producer groups, research and development corporations). Two aspects of nutrient management relevant to this report are phosphorus and the nutrient capital needed to increase soil carbon stocks across Australia (see Section 2.2.4).
Recent concerns that the world’s supply of phosphorus was being rapidly depleted and that ‘peak phosphorus’ was only a few decades away78 have been dispelled, due to recent upward revisions of world phosphate rock reserves and resources.79 However, the world supply of phosphorus is limited, and rising prices and market volatility are inevitable. More efficient use of phosphorus is therefore essential, especially in Australia, where the majority of soils used for agriculture are naturally deficient in phosphorus.
From phosphorus audits of Australian agricultural industries80 and farming systems81 it is clear that the use of phosphorus fertilisers in Australia is relatively inefficient. Most phosphorus is applied in the higher rainfall areas of southern Australia, and around 40% is applied to pastures. Nationally, approximately 20% of the phosphorus applied as fertiliser is extracted in food and fibre products for export, and about 5% is consumed domestically.78 The remaining 75% of the phosphorus applied in Australian agriculture accumulates in the soil,82-83 and some of this is lost to the environment, with detrimental impacts on waterways. The accumulation of phosphorus is greatest in soils across southern Australia. Apart from the environmental risks caused by this accumulation, the inefficiency has an economic cost that will increase as fertiliser prices rise. In contrast, many grazing systems in northern Australia have pastures and animal production that are limited by phosphorus availability.84 Careful fertiliser strategies and supplements will be needed in these systems.
Cultivation benefits agriculture by controlling weeds and creating suitably sized soil aggregates for a good seed bed. However, cultivation also disrupts microbiological activity and causes oxidation of organic matter. Its effect on soil organisms and organic matter has been likened to a fire through ploughed soil. Cultivation causes a decline in organic matter, which can lead to a general loss of fertility, unless counteracted by actions such as using fertilisers and rotating crops or pastures to restore organic matter levels. Loss of organic matter often leads to soil structural problems such as surface sealing and hard-setting.
Excessive cultivation was widespread during the first half of the 20th century, and it still remains a problem in some locations. During recent decades, techniques of conservation farming have been developed that emphasise retention of crop residues, appropriate rotations with legumes and reduced tillage. Maintaining soil cover on sloping land is especially important to protect against erosive rainfall. These changes are having a major influence on soil condition and trend (see Sections 2.2.4 and 2.2.6). Figure 5.9 provides a succinct summary of the great progress made by Australian farmers in reducing the intensity of tillage. This achievement required changes to agricultural machinery, crop rotations and methods for controlling pests, diseases and weeds. The transition to minimum tillage across most cropping lands during the past decade is a major advance by Australian farmers that reduces pressures on the land environment.
Heavy machines such as tractors, harvesters and trucks drive over most agricultural areas, compacting soils. Damage is greatest when the soil is wet. Some of the compaction can be undone through cultivation, although it is common for plough pans (a soil layer that is hard, compacted and roughly horizontal) to develop just below the depth of cultivation. The distribution of pressure under a heavy vehicle also results in a zone of compaction halfway between the wheels, usually at a depth of around 0.5 metres. This type of compaction is difficult to remove. Heavy animals can also compact wet soil, leading to a decline in pasture production. Most of the damage occurs in the upper part of the soil profile. The degree to which soil compaction limits plant growth and the efficient functioning of soils across Australia is not known with any certainty, although there are sufficient studies to suggest that it may be significant. Soil compaction affects landscape processes (e.g. carbon sequestration, water use efficiency of vegetation) and the general state of the environment. Controlled-traffic farming,h which addresses compaction by confining it to the smallest possible area, is being widely adopted and has the potential to alleviate further damage.
Forestry production systems comprise the harvesting of wood and nonwood products from native forests, and their regeneration after harvesting; the establishment, management, harvesting and reestablishment of plantation and other forms of planted forests; and sometimes other forest uses, such as apiary and domestic livestock grazing. Forestry production systems also require the management of bushfire risk, invasive species and other forest uses, and the delivery of ecosystem services.
Historically, the majority of native forest wood production has been in public forests. The area of public forest available for timber harvesting decreased by almost 50% nationally in the decade to 2008, as tenure was transferred to conservation reserves.1,12 No public native forests are harvested for wood production in the Australian Capital Territory, the Northern Territory or South Australia, and harvesting in south-east Queensland is being phased out by 2025. Further reductions in the extent and level of native forest harvesting in publicly managed forests are occurring in other states—for example, under the Tasmanian Forests Intergovernmental Agreement.85
Commercial timber harvesting is now limited to specified zones within the 6% (9.4 million hectares) of Australia’s native forests in public multiple-use tenures, private native forests, and plantations and other forms of planted forests. Firewood harvesting also takes place on these tenures. All native forest harvesting and most plantation practices are governed by codes of forest practice.86 Both wood and nonwood products are harvested from forests owned by Indigenous Australians, but typically at relatively small scales for art, handicraft products and local and cultural uses.1 Apiary and grazing are generally allowed on all tenures from which harvesting of forest products is permitted; each is specifically regulated.
The rapid expansion of plantation forests over the past decade noted in Section 2.1 has placed a number of pressures on land environmental values in regions where expansion was concentrated. These regions are parts of coastal Queensland, south-western Victoria, south-east South Australia, south-west Western Australia and eastern, northern and southern Tasmania.87 The pressure of most widespread concern has been the possible impact on catchment water yields, which can be locally significant, but is limited at a major catchment scale.88-89 The other major pressure was that of land clearing (see Section 3.2.2) associated with conversion of native to plantation forest, which occurred principally in Tasmania and to a lesser extent in the Northern Territory. However, at a continental scale, conversion of native forest to plantation accounted for only around 1% of all land clearing in the decade to 2010 (from Australia’s state of the forests: five yearly report 20081 and interpretation of data reported in Section 3.2.2).
The emergence of markets for carbon and other ecosystem services is likely to alter management objectives and regimes of both native and planted forests. Preliminary work (e.g. Keith et al.90, Polglase et al.91, Wentworth Group of Concerned Scientists92) has identified some of the possibilities, but further research is required to clarify optimum management regimes that account for other forest values and products, and for risks.29,93
Each year, new areas of land are covered with roads, car parks, buildings and other structures (see Chapter 10: Built environment, Section 3.1). When soil is capped with an impermeable layer, it effectively ceases to function as a biological entity. The consequences are more than a loss of land for agriculture, conservation or other uses. Capping soil changes the water balance of catchments (more run-off is produced from rainstorms over a shorter period) and reduces the area available for soil respiration and carbon sequestration.
During the 19th century, many urban centres were established on, or adjacent to, land highly suited to horticulture and cropping. The encroachment of urban and peri-urban development has seen the capping of this land. For economic reasons, it is highly unlikely that these good-quality soils will ever regain their biological function.
The loss of strategically valuable agricultural lands is a significant challenge for most state, territory and local governments. Various policies and planning mechanisms are now in place to protect and maintain remaining areas. However, the broader challenge posed by mining and coal-seam gas development in New South Wales and Queensland has heightened public debate and government engagement.94 The lack of detailed soil surveys that identify the location of the best agricultural soils impedes planning. The current information base does not allow optimal decision-making about where to locate development projects, due to the generally deficient information accessible to local planning authorities. The need to accurately map our best agricultural land has been recognised for decades.95
Compared with most countries, the mining industry in Australia is large, and it is responsible for much of the nation’s economic prosperity. Mining is a major industry in many regions, including Peel (bauxite, mineral sands), the Western Australian Goldfields (gold and nickel), the Pilbara (iron ore), the Hunter Valley (coal), the La Trobe Valley (coal) and the Bowen Basin (coal and gas). Australia has notable mining towns (e.g. Broken Hill, Mount Isa) and large mines (e.g. Ranger Uranium, Olympic Dam).
Environmental management in the mining industry before the 1970s was inadequate, and the legacy included contaminated and degraded land with chronic environmental problems (e.g. Victorian goldfields in the 19th century, Queenstown, Captains Flat mine).
Environmental impacts are now more actively managed, due to tighter environmental regulation and the need for companies to obtain a social licence to operate. However, the rapid expansion of the industry is continuing, and the scale of disturbance in some regions is transforming the landscape and causing profound environmental change. Notable examples include the Hunter and La Trobe valleys and the Bowen Basin. The scale of the current expansion, particularly for gas in eastern and north-western Australia, is resulting in conflicts over land use and the environment.94 These are set to continue and most likely intensify.
Soil has a remarkable ability to absorb and filter contaminants. As a result, most human waste is either buried in landfills or spread across the soil surface (land-based effluent disposal). However, it has been realised for some time that many contaminants cannot be safely disposed of in this manner, because they either do not break down into safe substances or they move from the disposal site (either to groundwater or as a gas to the atmosphere). The sophistication and regulation of waste disposal have improved markedly in recent decades. The Cooperative Research Centre for Contamination Assessment and Remediation of the Environment (CRC CARE) estimates that 160 000 contaminated sites potentially exist across Australia, containing as many as 75 000 different contaminants (R Naidu, CRC CARE, pers. comm., 2011). The centre quotes industry sources that estimate clean-up costs to be $2 billion per year, with the total remediation cost being much greater. While uncertainties remain about the scale of the problem, significant advances have been made in the development of remediation technologies that replace ‘dig and dump’ methods of disposal with a more effective, efficient, risk-based approach.
Some examples of soil contamination are described below:
- Fertiliser impurities—Impurities in fertilisers and soil amendments such as lime and gypsum can include cadmium, fluorine, lead and mercury. Cadmium has been of most concern, because it can move from soil to the edible portions of plants. In recent years, levels of cadmium in fertilisers have been reduced, and farming systems have been modified to lessen the problem. However, large areas of land that once received heavy applications of superphosphate over decades now have elevated levels of cadmium.
- Pesticides and herbicides—Many of the more harmful pesticides and herbicides have been banned or more tightly controlled. However, some can persist and adversely affect the environment, notably in areas that were, or still are, used for growing potatoes, tomatoes, cotton, bananas and sugar cane. Copper, arsenic and lead are contaminants associated with orchards and market gardens.
- Organochlorines—Soil at thousands of former cattle and sheep-dip sites are contaminated with organochlorines such as dichlorodiphenyltrichloroethane (DDT) and other pesticides such as arsenic-based compounds. Urbanisation and the construction of dwellings on or near such sites pose a serious threat to human health. Most of these sites have been identified and registered.