Laboratory Measurement

To determine salinity, the electrical conductivity (EC) is measured.  EC is the capacity of a substance to conduct or transmit electrical current. Pure water does not conduct electricity well, but as more salts are dissolved in the water, the conductivity increases.  In soil, these salts are mostly carbonates, sulfates, or chlorides of Na, Ca, Mg, and K.

The first step in EC determination is to create a paste of soil and water.  Use of a saturated soil paste is the convention, but you can use other ratios (e.g. 1:2 soil-water mixture).  The EC of the extract is then measured by immersing a conductivity electrode in the solution extracted from the soil, which is called the “saturation extract”. You must report the ratio of soil and water used with your results as it affects the amount and composition of salts extracted.  The SI units are decisiemens per meter (dS/m), which is equivalent to millimhos per cm (mmho/cm).

The following could also be determined on the same extract solution: sulfate (SO42-), bicarbonate (HCO3-), nitrate (NO3 ), chloride (Cl-), calcium (Ca2+), magnesium(Mg2+), sodium (Na+), potassium (K+).

Click here to download a video notes sheet before watching the following video.

Leave a Reply