Earth and Environmental Science
Home > Earth and Environmental Science > Core > Caring for the Country > Caring for the country: 3. Salinity of soils and water
9.4 Caring for the country: 3. Salinity of soils and water
| Syllabus reference (October 2002 version) | ||
|---|---|---|
3. Salinity of soils and water |
Students learn to: | Students: |
Extract from Earth and Environmental Science Stage 6 Syllabus (Amended October
2002). © Board of Studies, NSW
[Edit: 24Jul 08]
Prior Learning: Preliminary module 8.4 (subsection 4)
Background: Recently, we have been hearing more and more of the problems of salinity in the countryside of Australia. First it was the Murray Basin, in parts of Victoria and NSW, and then it was parts of the wheat belt of south-western Western Australia with major salinity problems. We now realise that the widespread clearing of land has been a major factor in causing salinity. It is a billion dollar problem that must be remedied. There may well be value in seeking advice from the original custodians of the land who managed it effectively over a large period of time.
identify regions of Australia with naturally saline soils
- One naturally saline area is northern South Australia and southern Northern Territory with lakes such as Lake Eyre, Lake Torrens, Lake Frome, and Lake Gairdner. These lakes are the remains of a vast inland sea that once extended south from the Gulf of Carpentaria. During the dry season many of the salt lakes become salt-encrusted swamp beds or clay pans.
- Parts of the Murray-Darling Basin have naturally saline seepages and scalds. Scalds are areas where salt has come to the surface, leaving a bare crusty area where nothing can grow due to the high salinity.
- Parts of southern Western Australia have natural salt lakes.
examine the possible consequences for soil salinity of land clearing and irrigation and outline precautions that could minimise the problem in each case
Land clearing
- When non-indigenous people settled on the land and cleared it for
the purpose of pasture and agriculture, they used European methods of farming, unaware
that these methods were not suitable to Australian soils. Removal of trees that take up
large amounts of water and the replacement of them with shallow rooted plants such as
crops or pasture that take up very little water, means that there will be more water in
the soil. As this water percolates through the soil it will add to the amount of water in
the watertable. This results in the watertable rising and bringing the salts with it to
the surface.
- Precautions that may minimise the problem include:
- replacing the trees that were removed with native vegetation
- leaving trees in paddocks and along the edges of paddocks.
- These trees provide shade for stock as well as help reduce erosion.
The use of deep-rooted pasture crops, such as lucerne, will keep the watertable lower.
- Already badly damaged sites can be planted with saltbush or other salt tolerant species. This will help remove the salt, so that less salt tolerant plants will survive when planted in the soil.
Irrigation
- The addition of extra water by irrigation may cause the watertable
to rise more rapidly. The irrigation water may contain small concentrations of salts, and
when the water evaporates, it leaves this salt in the surface layers of the soil. The
removal of trees in the preparation of the soil for irrigation, and their replacement with
shallow rooted plants, adds to the rising watertable.
- In some situations, where the watertable is low, irrigation has a
positive effect by washing salt from around the plants down to the watertable. Research is
currently being conducted to determine appropriate strategies in particular locations.
- Precautions include:
- the use of alternatives to flood irrigation such as trickle or sprinkler;
- improved drainage in paddocks so the water doesn't sit for extended periods, but flows across it;
- the planting of trees around the edge of paddocks, and in pastures to reduce groundwater levels.
- Carefully checking soil types for suitability before water licences are granted to irrigators.
For further information on areas affected by salinity 
and what can be done about
it. NSW Department of Environment and Climate Change, NSW State of the Environment,
2006. Click on whichever aspect of salinity you want to investigate.
identify data sources and gather, process and present information as a case study of a successful rehabilitation program of a salt-affected area, including:
- the origins of the problem
- the impact of the salinity problem on the biotic and abiotic environment
- the rehabilitation strategy used and the scientific basis for this strategy
To identify data sources and gather information look on the Internet for a case study. Try using key words such as urban salinity and, for examples of urban salinity in rural NSW, include the names of local communities such as Dubbo or Armidale.
A case study: A case study
to reduce dryland salinity on a Temora farm .
Proceedings of the 10th Australian Agronomy Conference, Hobart, 2001.
If you live in a rural area you could include your own first hand field study findings in this case study.
When you process the information use the three points provided in the syllabus (origins, impact, rehabilitation strategy) to structure your case study and report.
When you present your information include tables, graphs and diagrams where appropriate.
|