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Environmental impacts of agriculture
The combined impacts of land and water use for agricultural production have been substantial. For example:
Tables 16.5 and 16.6 show the area affected by three types of land degradation, as well as their estimated annual cost to agricultural production. Water quality is discussed in an article following Environment, and hence it will not be considered here.
Salinity, sodicity and acidity are all naturally occurring conditions of Australian soils, but these have been exacerbated by agricultural activities. Sodicity is a condition in which the sodium levels of the soil increase to the extent that they affect the physical properties of the soil. Sodic soils are prone to waterlogging. Acidity is a condition in which the concentration of hydrogen ions increases in the soil, which can cause the death of many plant species. Salinity is the build-up of salts in the soil, which also can kill plants.
In recent years salinity has gained prominence as a national environmental issue (see for example, MDBC 1999; Commonwealth of Australia 2000; NLWRA 2001). Early results from the 2001 ABS Agricultural Census show that around 26,000 farmers have salinity and/or are managing salinity on their properties. Table 16.7 shows that the proportion of farms reporting managing for salinity is greater than those reporting salinity, which is an indication that farmers are taking action to prevent or reduce the impact of salinity on agricultural land.
Various activities have been used by farmers to manage or prevent salinity. The type of management adopted depends on the nature of the farm: cattle farmers adopt practices different from those used by orchardists. Three commonly promoted salinity management actions are the planting of lucerne, salt-tolerant pastures and trees. Others include pumping groundwater (to lower water tables) and digging drains, especially where the salinity is severe or high value crops (e.g. grapes) are involved.
The impacts of salinity extend beyond the agriculture sector. Roads, houses and water supply infrastructure can all be degraded by it. Over four states (New South Wales, Victoria, South Australia and Western Australia) the road, buildings and/or water supply infrastructure of 68 towns are at risk of damage from salinity. Biodiversity is also at risk through the loss and degradation of native vegetation. Across Australia around 630,000 ha of native vegetation and 80 wetlands, including wetlands of international importance, are at risk (NLWRA 2001).
One factor contributing to salinity is the rise in water tables due to increased amounts of water entering underground water bodies from irrigated land. This ultimately results in increased salt loads entering river systems. Reduced river flows, brought about by the construction of dams, weirs and water diversions, compound the problem as the flow is insufficient to dilute saline groundwater inflows (ABS 1996).
In recent years the area irrigated has increased substantially. Between 1990 and 2000 the area of irrigated land increased by more than half a million ha or 30%. The growth in irrigated area was greatest in Queensland, where an additional 236,000 ha (or 76%) were irrigated in 2000, compared to the area irrigated in 1990 (table 16.8).
Irrigation can also cause a decline in soil structure and water quality, while the method of irrigation used influences the efficiency of water use and impact on the environment (Smith 1998). Impacts on water quality result from the high levels of fertiliser use in conjunction with some irrigation methods. Continued awareness of the need for greater efficiency and technological advancements can be expected to improve land management practices and reduce the decline in the health of land and water assets. For example, there has been a growth in the use of irrigation methods that are more efficient in terms of water delivery. In 2000 around 30% of irrigators reported using spray, micro spray or drip irrigation methods compared to 23% in 1990 (table 16.9).
A number of factors affect the choice of irrigation methods used by farmers. These include cost, available technology, soil type, type of crop, climate and topography. In 1999-2000, furrow or flood irrigation methods were used for nearly 70% of all irrigated land. Flood irrigation, used on the majority of pastures and cereal crops, is popular probably because it is cheaper than the other methods available (Vic SoE 1991). If not managed correctly, furrow and flood irrigation can be highly inefficient and have detrimental effects on the water table and surrounding water bodies. However, for some crops, like rice, it is essential.
In 1999-2000, the spray method was used on approximately 22% of irrigated land. Spray irrigation has a higher installation cost and can be used for the application of slightly more saline water (generally from groundwater sources). The spray method produces less waterlogging than the flooding method, but is ineffective in high winds and can sometimes wash fertilisers from crops. Drip irrigation, also know as micro or trickle irrigation, is used on a smaller scale than other methods, and accounted for approximately 8% of irrigated land in 1999-2000. It is used on high value crops like grapes, citrus and tomatoes. Although the drip method is highly efficient, as evaporation losses are substantially reduced, it has higher installation and maintenance costs. Other technological innovations, such as laser levelling, have improved water efficiency (Smith 1998).
Many other land management practices can have environmental benefits. The planting of trees and fencing of native vegetation are two obvious examples (see ABS 2001a; Environment). These protect land and water quality as well as creating habitat for native animals and plants. Less obvious practices also help to make a difference. For example, stubble management methods can influence rates of soil erosion and the amount of organic matter retained in the soil (stubble is what remains of plants after crops have been harvested). In 2000-01 around 5 million ha of stubble were left intact (table 16.10). This stubble would have protected the soil from erosion by wind and rain.
The increasing use of more efficient irrigation methods, the implementation of salinity management activities and adoption of other land use practices are an indication that farmers are more aware of the environmental impact of their activities than in the past. Much of the impact on the environment is the result of historical land management decisions, and has taken decades to manifest. The impact of agriculture on the environment can be reduced and there are a number of community groups and government programs dedicated to achieving this. However, it is likely that the damage already done will take decades to abate and repair.
ABS (Australian Bureau of Statistics) 1991, Summary of Crops, Australia, cat. no. 7330.0, ABS, Canberra.
ABS 1996, Australian Agriculture and the Environment, cat. no. 4606.0, ABS, Canberra.
ABS 2000, Water Account for Australia, 1993-94 to 1996-97, cat. no. 4610.0, ABS, Canberra.
ABS 2001a, Agriculture Australia 1999-2000, cat. no. 7113.0, ABS, Canberra.
ABS 2001b, Australia's Environment: Issues and Trends, cat. no. 4613.0, ABS, Canberra.
ABS 2002, Australia's Environment: Issues and Trends, 2002, cat. no. 4613.0, ABS, Canberra.
AGO (Australian Greenhouse Office) 2001, Australian National Greenhouse Gas Inventory: Land Use Change and Forestry Sector 1990-1999, AGO, Canberra.
Commonwealth Department of the Environment and Heritage 2001, Australia State of the Environment Report 2001, CSIRO Publishing, Canberra.
Commonwealth of Australia 2000, National Action Plan for salinity and water quality (Information Booklet), Commonwealth of Australia, Canberra.
Hamblin A 2001, 'Land', Australia State of the Environment Report 2001 (Theme Report), CSIRO Publishing on behalf of the Department of Environment and Heritage, Canberra.
MDBC (Murray-Darling Basin Commission) 1999, The Salinity Audit of the Murray-Darling Basin - A 100 Year Perspective, MDBC, Canberra.
NFI (National Forest Inventory) 1998, Australia's State of the Forests Report, National Forest Inventory, Bureau of Rural Sciences, Canberra.
NLWRA (national Land and Water Resource Audit) 2001, Australian Dryland Salinity Assessment 2000, NLWRA, Canberra.
NLWRA 2002, Theme Six Report, NLWRA, Canberra.
Smith DI 1998, Water in Australia, Resources and Management, Oxford University Press, Melbourne.
Vic SoE (State of the Environment Committee) 1991, Agriculture and Victoria's Environment. Resource Report, Office of the Commissioner for the Environment, Melbourne.
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