Understanding Electrical Conductivity (EC) of Hydroponics nutrient solution

Electrical conductivity is a measure of the nutrient solution’s concentration through its ability to conduct electricity. Pure water does not conduct electricity, but any water having solutes (elements) added to it has the capacity to conduct electricity. The EC of a nutrient solution can significantly affect plant growth. . Electrical conductivity (EC) is frequently used as a means of determining elemental replenishment needs in closed recirculating nutrient solution growing systems.

An EC measurement of the nutrient solution is used to determine nutrient element top up levels. Note that the EC value indicates the total strength of the solution but nothing about the balance of nutrients within it, so, its use in the management of hydroponic solutions is limited.

The raw water used for the hydroponic solution may itself contain dissolved nutrients which will contribute to the strength of the solution. A water quality test will ascertain which nutrients are present and their concentrations, and should be taken into account when making up the hydroponic solution

 Units of measurement

decisiemens per meter (dS/m)
millisiemens per centimeter (mS/cm)
microsiemens per centimeter (μS/cm)
(1 dS/m = 1 mS/cm = 1000 μS/cm = 1 mmho/cm)
(1 μS/cm = 0.001 dS/m)
EC (in dS/m) x 640 = TDS [in mg/L (ppm)]
(approximate measurement, depends on type of salt)
cf. (conductivity factor) of 10 = 1 dS/m

Electrical conductivity adjustment of the nutrient solution is recommended when the plants are to be stressed, as water uptake by the plant is reduced when the EC of the nutrient solution and/or rooting
Medium is increased. Change in the electrical conductivity (EC) of a solution surrounding the root, or may alter the pH of the surrounding solution.
High EC in the rooting medium can result in plant wilting on high atmospheric demand days because insufficient water is being taken up through the plant roots to keep the plant turgid.

The target EC of a nutrient solution can vary according to the crop being grown, stage of growth and climatic conditions. Most nutrient solution formulas have a fairly low [<3.0 dS/m (mmhos/cm)] EC when initially made.

In hot, low-humidity days, if the water loss is not replaced, the EC of the nutrient solution will rise. The EC of the nutrient solution, and particularly that of the solution in the medium, becomes critical when it exceeds 4.0 dS/m.
In an NFT system most leafy greens such as Basil, Choy Sum, Tat Soi, and Coriander Pak Choy grew best in the nutrient solution managed in an EC range of 1.5-2.5 dS/m.