Home About Us Our Services Publications Testing Submissions Contact Us Links

How salinity is measured

Water and soil salinity are measured by passing an electric current between the two electrodes of a salinity meter in a sample. The electrical conductivity, or EC, of a soil or water sample is influenced by the concentration and composition of dissolved salts. Salts increase the ability of a solution to conduct an electrical current, so a high EC value indicates a high salinity level.

EC is also used as a measurement unit of salinity. The table below shows the different units used to measure salinity and their relationship to each other.

* ppm is only an estimate and depends on temperature and types of salt. The multiplier, shown here as x0.64, ranges between x0.5 and x0.7.

Salinity can be measured in a number of ways:

1. Simple field tests using a hand-held salinity meter are quick and easy and are useful for conducting preliminary investigations, point-sampling of selected areas and ongoing monitoring activities.
2. Electromagnetic mapping can be used to characterise and map spatial variability of soil and apparent salinity over larger areas. This is a valuable tool for land use planning and provides a rapid assessment of differences across a paddock. It allows areas of low and high electrical conductivity and thus salinity to be identified.
3. More precise soil and water laboratory tests can be performed and should be used to confirm preliminary field testing where a possible salinity problem is suspected.

Salinity measurements are often reported with subscript abbreviations to indicate the origin of the sample tested and the method used to determine the salinity measurement. The method used influences the accuracy of the results and confidence in interpretation. Common abbreviations and their descriptions are explained below.

EC_w is the salinity of water. This can be measured in the field or the laboratory. It is sometimes written as EC_iw, where iw denotes irrigation water.

EC_1:5 is the first of three steps to estimate soil salinity (EC_e). It is determined by mixing 1 part soil with 5 parts distilled or deionised water. After mixing, the sediment is allowed to settle, then the EC of the solution is tested. An EC_1:5 can be performed in the field or the laboratory.

EC_e is the estimated amount of salt in the soil. It is estimated by multiplying the EC_1:5 value by an appropriate factor related to the soil texture of the sample. This can be determined in the field or the laboratory.

EC_se is the electrical conductivity of a saturated soil extract. It needs to be conducted by a reputable laboratory.

EC_a is the apparent electrical conductivity. It is a measure of bulk electrical conductivity of undisturbed soil in the field. It is measured with an electromagnetic instrument (EM38 or EM31) in a soil survey.

Further reading

Deb Slinger and Kath Tension, Salinity Glove Box Guide for NSW Murray & Murrumbidgee, NSW Department of Primary Industries, 2005.