Dryland salinity is the process where salts stored below the surface of the ground are brought close to the surface by a rising watertable. Dryland salinity in South Australia has significant impacts on the state’s land, water and biodiversity assets, and on the productivity and quality of our crops and pastures. In many parts of the state, historical clearance of native vegetation and its replacement with annual crops and pastures has resulted in higher groundwater levels. This has caused streams, wetlands, native vegetation and agricultural land to become salt affected, waterlogged and degraded. In addition, dryland salinity has significant economic and social impacts, particularly in regional communities, with the high costs associated with lost agricultural production and salt damage to roads, buildings and other infrastructure.
An assessment in 2000 showed that there were approximately 360,000 hectares affected by dryland salinity in South Australia, which is 2.3% of all land in the agricultural zone. From the mid 1990s to 2008, the majority of groundwater levels across South Australia were exhibiting stable or falling trends due to lower than average rainfall experienced across South Australia’s agricultural districts. As a result, the risk that salinity posed to valuable assets across the state had decreased.
However, in 2009-11, in response to above average annual rainfall, episodic rises in groundwater levels have been observed across South Australia. If these rises in groundwater are sustained, there is a corresponding increase in the risk of new or reactivated outbreaks of dryland salinity.
Of more immediate concern are those areas where episodic recharge has brought shallow groundwater to within a critical salinisation depth (less than 2 m, which then induces surface soil salinity) of the soil surface, and where long-term rising trends in depth to groundwater have continued unabated, such as on the Northern Adelaide Plains.
The future impact and risk of dryland salinity will depend largely on future rainfall patterns including climate change, the nature of the groundwater system and the effectiveness of interventions to slow or halt a rise in groundwater.
Approximately 200,000 ha of the Upper South East is afflicted, making it the most severely affected area in the state. With the successful completion of the Upper South East Dryland Salinity and Flood Management Program, the drawdown effect associated with the drainage network has reduced the risk of salinity over an estimated area of more than 100,000 ha.
Practical and profitable options for large-scale adoption of perennial plant systems and associated recharge reduction are being developed through the State government's partnership with the Future Farm Industries Cooperative Research Centre (FFICRC).
The NRM Regional Boards have prepared regional NRM plans and investment strategies for integrated NRM, inclusive of salinity management. On-ground works and other programs to promote the management of dryland salinity through recharge reduction have been undertaken in all agricultural regions. Most projects have involved an integrated package of NRM and sustainable land management outcomes, including dryland salinity management, soil erosion control, water quality and habitat and native vegetation management.
Continued research is needed to develop practical and economic perennial plant options for effective recharge management at the large scale required for dryland salinity management, including further development of a broader range of options for managing saline land and water.
Monitoring and evaluation of dryland salinity (using agreed indicator and protocol frameworks) should continue through South Australia’s monitoring and evaluation framework.
There needs to be ongoing assessment of the impacts of climate change on the future extent and risk of dryland salinity.