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Plant/Animal Production

Salinity

This material addresses aspects of the following syllabus outcomes:

A student:

H1.1 explains the influence of the physical, biological, social, historical and economic factors on sustainable agricultural production.

H2.1 describes the inputs, processes and interactions of plant production systems.

The work presented in the following section contributes towards understanding the following syllabus content area:

Students learn about:

sustainable agricultural production
the farming practices that have led to soil degradation such as salination, acidification, soil structure decline and erosion, and the effects of these on soil and water.

Extract from Stage 6 Agriculture Syllabus © Board of Studies NSW 1999.

Salinity

Salinity is, simply, the presence of salt in the root zone of plants. It is an enormous problem in Australia causing great loss of production. The cost to Australia each year is in excess of $270 million. Due to the extent of this problem, the Government is active in identifying and studying salt affected areas of Australia.

When discussing salinity the following terms are often used:

Recharge Where water is added to the ground water.
Discharge Where water is lost from the ground water.

If Recharge > Discharge the level of the watertable will rise.

There are two types of salination caused by farming practices in Australia: dryland salinity and irrigation salinity.

Dryland salinity

This is salinity in non-irrigated rural areas. It affects 2.5 million ha of Australian farmland.

Cause

Clearing of native vegetation. Since the first white settlement of Australia enormous numbers of high water using native trees, shrubs and grasses have been replaced with shallow rooted crops and pastures. These introduced plants take less water from the ground water (i.e. reduce discharge).

As less water is taken from the system, the level of the watertable rises bringing with it dissolved salts.

Clearing means there is less discharge. A rising water table brings salts in to the root zone. The result is dryland salinity.

Effects

Reduced plant productivity because the plants have difficulty extracting water from the soil.
Dissolved sodium, chloride and borates can be toxic to plants and may raise soil pH.
Soil structure may be damaged leading to soil instability and erosion.
Death of native vegetation.
Water becomes unsuitable for livestock, humans and irrigation.

Solutions

Plant salt tolerant pasture species e.g marsh grass, tall wheat grass & saltbush.
Tree planting.
Change from shallow rooted annual pastures to deep-rooted perennial pastures such as lucerne and phalaris.
Avoid overgrazing.
Contour banks and drainage to control water flow.

Irrigation salinity

This type of salination occurs in areas subject to irrigation, not just natural rainfall (i.e. greatly increased recharge.).

It is estimated that 70 - 80% of irrigated land in NSW is under threat from rising watertables.

Cause

When the volume of added water is greater then the evaporation and transpiration occurring , the excess water goes into the groundwater , causing the watertable to rise. This problem is compounded by the high rate of clearing that precedes irrigation.

Clearing and irrigation results in a rising watertable. This is called irrigation salinity.

Effects

These are the same as in dryland salinity, however, the irrigation water usually becomes saline too, so the effects are quickly magnified.

Finding more information

There are many sources of detailed information regarding salinity and other soil degradation. Some to try are: