Electrical conductivity: for healthy soil and efficient irrigation

The electrical conductivity (EC) is the sum of the conductivities of the different types of ions present.

It is a physical parameter that measures, at a given temperature,  the ability of a substance to conduct electric current.

Its value is determined by the presence of ions and their mobility in solution.

In agronomy, the EC is one of the most commonly used parameters to measure the salinity of the saturated extract (ECe) or water (ECw), as its value is proportional to the amount of salts in solution contained in it. (Rhoades, 1981). Its value is measured in deciSiemens / metre (dS/m) or millimhos / centimetre (mmho/cm) where1 dS/m = 1 mmho/cm.

The main objective of EC analysis in soils is to determine whether soluble salts are present in sufficient quantities to affect seed germination, plant growth or plant water uptake.

The ECe is influenced by the different physical and chemical properties of the soil.

FieldScout Direct Soil EC Meter

For this reason conductivity will increase to the extent that the soil contains:

• Higher moisture content. Soils with higher porosity or lower bulk density will have higher water storage capacity and can reach higher values of electrical conductivity (Samouëlian et al 2005).
• Higher content of dissolved salts. Increased salinity and cation exchange capacity (Rhoades and Corwin, 1981).
• Fine texture. Because of their higher water storage capacity and higher cation exchange capacity, clays have higher conductivity values.

In water, the EC is measured for the purpose of determining the WATER QUALITY irrigation and flushing requirements of a soil irrigated with saline water.

The EC does not differentiate what type of salts are in the sample but allows us to determine the total amount of dissolved salts (TDS), defined as the total ion concentration in solution expressed in mg/l or ppm, where:

TDS (mg/l) = EC (dS/m) x 640 if EC ˂ 5 dS/m

TDS (mg/l) = EC (dS/m) x 780 if EC ˃ 5 dS/m

(Source: Robert N. Carrow and Ronny R. Duncan)