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Salinity
Salinity is one of Australia’s greatest environmental challenges. The cost of lost agricultural production and damage to the environment is likely to climb above $1 billion a year.
Scientists also predict that thousands of Australia’s unique native plant species run a high risk of becoming extinct unless we can halt the spread of dryland salinity.
Salinity is the presence of soluble salts in soil or water. Salts are naturally found in groundwater and become a problem when the water table slowly rises toward the soil surface. This occurs when more water enters the system from rainfall and irrigation than leaves the system through evaporation or use by vegetation.
Changes in land management including removal of vegetation and over-watering have increased the salinity problem in some areas.
There are three common types of salinity:
- dryland salinity
- irrigation salinity
- urban salinity.
Dry land salinity is the most common and involves the watertable rising to near the plant root zone and the build up of salt on the soil surface in non-irrigated areas. It is usually caused by changing land use leading to fewer deep-rooted plants using water from the watertable.
Farming activities that contribute to dryland salinity include:
- removing vegetation
- annual cropping
- overgrazing
- long fallow periods.
Irrigation salinity involves the waterlogging of soil and the watertable rising to near the plant root zone. It is usually caused by continually applying water by irrigation. Irrigation salinity can be influenced by:
- soil type
- drainage
- land management
- use of salty water for irrigation.
Both types of salinity can cause a loss of agricultural productivity. Most vegetation cannot tolerate salty soil and water in the plant root zone. They are affected by stunted growth, nutrient deficiencies and will often die.
Salinity can also increase fertiliser needs, reduce the quality of ground and surface water and degrade wildlife habitats.
Management of salinity
To manage salinity, the amount of water entering the watertable must be reduced and the amount of water used from the watertable must be increased.
Actions that reduce the amount of water entering the watertable include:
- removing excess water from paddocks through the use of laser levelling and surface drains
- removing excess sub-surface water through ground water pumping
- practising irrigation water-use efficiency
- avoiding periods of bare ground
- conservatively stocking
Actions that increase the use of water from the watertable include:
- increasing the growth of deep-rooted vegetation such as perennial pastures
- introducing salt tolerant fodder plants (salt bush) and agroforestry plantations
- improving the health of existing vegetation
- increasing crop yield
- growing high-water use crops.
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