Sodicity is a major cause of land degradation in the Sydney drinking water catchments. It is caused by high concentrations of sodium which is generally attached to clay particles of the soil. As a result, clay particles in the soil lose their tendency to stick together when wet. This leads to unstable soils that may erode or become impermeable to water and plant roots.
Signs of sodic soil are poor water infiltration, surface crusting, waterlogging, collapsing areas which appear to result from underground tunnelling and piping, and cloudy water in dams and creeks that never settles out.
Sodicity is most common in the subsoil. Soil structural problems from sodicity increase when soil organic matter is low. Having a good groundcover helps stabilise the topsoil and retain its organic matter content, and the risk of sodic subsoils becoming exposed to run-off and erosion is reduced.
What you can do
- Maintain more than 80 percent groundcover to improve soil structure and increase soil organic matter.
- Look for signs of sodic soils on your property (soil crusting, soil sealing, dense and compacted soil, sign of waterlogging, cloudy water in streams and dams)
- Know where the sodic soils are on your farm - do a LANDSCAN course.
- Retain topsoil and minimise disturbance and exposure of sodic soils.
- Exclude stock from eroded gullies and revegetate to prevent further erosion.
- Conduct a soil test that includes a measure of the Exchangeable Sodium Percentage (ESP) - ESP of 6 percent or more indicates a sodic soil.