Publications
Weeds
Soils
Species Lists
Catchments
Phillips Brook
Wattening
Jimperding
Boyagerring
Community
Friends of the River
Seed Orchard
Naturalists Club
Issues
Salinity
Sodicity
Revegetation
Erosion
Livestock Management
Advice for the Small Landholder
Small Landholder Information Service
Spatial data
Shared Land Information Platform
Pest Plants and Animals
Feral Rabbit data
Our Strategy
For the Future
Salinity
What causes land to be affected by salinity?Many West Australian soils contain salt. Before clearing this salt was locked in the soil by deep-rooted native vegetation (trees). Trees act as pumps to use up water deep in the soil profile. Rain then washed the salt through the profile keeping it away from annuals or plants that have shallow root systems. Extensive clearing has meant that there is a reduced capacity for the land to use up excess water. This allows the water table to rise, bringing salt up into the root zone or to the surface. These areas are then unsuitable for growing crops.
Why is salinity a problem?
If plant roots are sitting in saline water then reverse osmosis occurs. Osmosis is the process where the content of the cells are drawn out of the plant rather than drawn in, so the plant dries out.
Measuring Salinity
Salinity is measured in a number of different units. In this instance we are using mS/cm.
'Conductivity' is the ability for a material to conduct electrical current. The unit of electricity measured is in 'Siemens'(named after the German inventor Ernst Werner von Siemens). The amount of electricity is very small, so it is measured in millisiemens. In this context, it is the ability for electricity to conduct over a centimetre (mS/cm).
Salt is a good conductor of electricity, so the more salt (or salinity) the more electricity conducted (the higher mS/cm measurement).
Most living plants and animals, apart from those that live in our oceans, have a low tolerance to high salt levels. Even at lower levels, humans, livestock, crops and soils all have varied tolerances.
Salt Tolerance Ranges
less than 1mS/cm - Fresh, and suitable for human consumption
1-1.8 mS/cm - Marginal - acceptable as drinking water and irrigation
2-9mS/cm - Brackish - acceptable for most stock and irrigation
9-23mS/cm - Low Saline - limited farm use
10mS/cm - the maximum for horses
11mS/cm - the maximum for lambs, weaners and breeding ewes
16.5 mS/cm - the maximum for beef cattle
23mS/cm - unacceptable for most stock except in an emergency, and the maximum limit for sheep
20-45mS/cm - highly saline
more than 45mS/cm - hypersaline
There are many different units that can be used when measuring salinity.
Conversions:
mS/cm x 550 = total soluable salts mg/l (milligrammes per litre)
mS x 38.5 = grains per gallon (gr/gl)
mS/cm x 1000 = uS/cm (uS = microsiemens)
mS/cm x 100 = mS/m
mg/l divided by 1 = ppm (parts per million)
mg/l divided by 100 = ppt (parts per thousand)
mg/l divided by 14.25 = gr/gl
In the Avon region we expect seasonal fluctuations in conductivity readings with the variations in stream flow. With the initial flow, readings increase dramatically, then with the stronger flows, readings will decrease. As water levels drop readings may increase.
Management
Improve the use of water where it falls on the farm; this will reduce the amount which is lost to recharge.
Make strategic use of revegetation or protection of existing vegetation in recharge areas high in the landscape and discharge areas low in the landscape.
Plant deep-rooted perrenial crops that will use more water from further down in the soil profile. Drainage can be useful in some situations and soil types but often this is just shifting the problem down stream. The benefits of drains need to be asssed by a professional before being undertaken, as they are expensive. When drains are found to be useful, they should be combined with revegetation and the use of perrenials in a farming system.
It should be noted that there are specific regulations that need to be addressed prior to undertaking any drainage project.
Reference: "How salty is the water" Ribbons of Blue, Waterwatch WA
Further reading - Toodyay Landcare Plan for the Future.
Back to the Home Page
