Salinity is one of the biggest issues with water quality.
You can easily test the salinity of water with a Salinity Meter which measures the electrical conductivity of the water. As the salt level of the water increases, so does the conductivity.
Water salinity measurements are expressed as microsiemens per centimetre (mS/cm) or sometimes as decisiemens per metre (dS/m).
Conversion factors for differing measurements of electrical conductivity (EC):
1mS/m (milli-Siemens per metre) =10µS/cm (micro-Siemens per centimetre)
1mS/cm(milli-Siemens per centimetre)=100mS/m (milli-Siemens per metre)
1dS/m (deci-Siemens per metre)=100mS/m (milli-Siemens per metre)
1dS/m (deci-Siemens per metre)=1,000 µS/cm (micro-Siemens per centimetre)
(Note: many salinity meters measure in units of mS/cm).
Microsiemens per centimetre multiplied by 0.64 = parts per million (ppm)
This photo shows how over-irrigation can flood the soil, leading to an increase in salinity, making soils incapable of supporting plant growth, and affecting people and animals.
Salts in irrigation water affect crop performance by:
- outcompeting the roots for moisture, reducing growth and yield.
- salts reduce shoot growth and yield.
- Some elements of salts such as chlorides, sodium or boron can have toxic impacts on plants.
Other factors also affect the ability of plants to cope with salinity.
Factors such as the soils ability to drain, the method of irrigation, the level of rainfall and the plant’s natural tolerance to salinity are further matters to consider. Some plants can accept a higher salinity level in water than others (known as salt tolerant).
In general, if salinity is less than 0.8 dS/m, the water is suitable for most crops and pastures on moderately to well-drained soils.
If salinity is more than 2.3 dS/m the water is not suitable for continuous use for irrigating most crops or pastures.
The maximum advisable levels for stock are shown in the table below. It should be noted that the standard unit for measurement of EC values differs from place to place. In this module, the unit used will be mS/m, the same standard as that used by the W.A. Department of Agriculture. Note; Some conversions are provided above.
If stock water is saline animals will tend to avoid it initially. If the stock water is only moderately saline then production levels may still be maintained, with negligible loss, once the stock have had a chance to adapt to the water (though there may be some side effects such as scours and it is preferable to not use this water for lactating stock).
With highly saline water, the initial reluctance to drink will lead to severe thirst and the animals will then drink large amounts of saline water to quench their thirst. Other reasons for the large intake are the taste and partly to allow greater water turnover so that the body can regulate the salt balance. Ultimately, the intake of highly saline water will lead to health problems in the stock.
In 2001 Kevin Moir, a western Australian sheep farmer got involved with Topoclimate Farm Plan Mapping along with eight of his neighbours. He initially wondered why Topoclimate survey staff were measuring water quality (pH and salinity) in the twenty-five dams that serviced his Wilga property near Collie and admits he didn’t consider this a priority for mapping and measurement.
Kevin was then pleasantly surprised when the water quality testing revealed that the dam in one of his best paddocks was so salty that it was unlikely that stock would drink from the dam. “I always wondered why, when I put my young lambs on good pasture in this paddock, they went backwards in condition.” Kevin said. “Now I realise that it was because they didn’t have access to clean fresh water, even though the dam was full.”
Now that the problem has been identified by the Topoclimate staff, Kevin has drained the dam and allowed it to refill from rainwater and intends to retest the water on a regular basis.
