What is EC?

What is EC?

Electrical conductivity or "EC" is a measure of the “total salts” concentration in the nutrient solution (drip, slab or drain).

It is expressed in milliSiemens per linear centimeter (mS/cm) or microSiemens per linear centimeter (mS/cm) where 1 mS = 1,000 mS. The conductivity of a given solution can change with temperature for this reason most nutrient solution analysis is carried out at 20oC.

The higher the “total salts” concentration in a substrate the higher the EC. An EC will only be registered when inorganic ions are present in solution. Examples of inorganic fertiliser ions are N, P, K, Ca, Mg, etc. Urea, an organic molecule, will not contribute to the EC of a solution because it cannot conduct electricity the way a calcium (Ca) ion or a nitrate-nitrogen (NO3-N) ion can.

 

The required EC for optimum plant growth will depend on the crop and variety being grown the physiological stage of plant development and the prevailing environmental conditions both inside and outside the greenhouse.

Why is it important to monitor EC?

The EC of the nutrient solution influences the growth and development of the plant. During the winter months a higher EC is used as this restricts the uptake of water. As a result, the cells in the plant do not elongate or "grow" as much. They remain smaller and have a thicker, stronger cell wall. The plant then appears darker, shorter and with smaller leaves.  In this situation, the plants put relatively more energy into the formation of flowers and fruit (a generative response).  If the EC is too low in poor light conditions (i.e. winter), the plant will produce too much leaf growth and too little fruit growth and hence will be too vegetative.

Conversely, a high EC under high light conditions (summer) will restrict water absorption too much and therefore the ability of the plant to cool itself via transpiration. Consequently, the crop will become stressed.

The EC also influences production and fruit quality. In general, a higher EC in the root zone environment leads to lower production and smaller fruit size. This is because the cells in the fruits take up less water, which results in a lower fresh weight. However, a higher EC results in better fruit taste. Therefore a compromise must be struck between fruit quality, yield and the vegetative and generative development for the crop.

It is important therefore to maintain the correct delta EC within the root zone environment (measured as the difference between the slab EC and drip EC). The value for delta EC differs for each crop type and time of year. For more details please refer to the crop specific water management guidelines for the Master™ slab by clicking here.

 

 

Monitoring the EC in the slab

Monitoring EC in the slab is an essential part of weekly nutritional monitoring and should be undertaken on a daily basis. Sampling should take place in a number of representative slabs in order for a meaningful and accurate assessment to be made. Sampling is easy, simply push a syringe into the slab and extract a small quantity of nutrient solution (100 ml) and place this into the cup of the EC meter for a direct reading. Calculate the value for delta EC and plot this on a graph this will make it easier to identify trends.  Alternatively the slab EC can be monitored directly over the course of the day and the results graphed automatically using Grodan's continuous water content meter (WCM-C).  The WCM-C also measures and produces a graphical output of the slab water content and slab temperature.  For more information on the WCM-C contact our distributors in the UK by clicking here.

Tips for accurate EC measuring using a portable meter

  • Calibrate the EC meter regularly using standard solutions.
  • Check the battery status, low batteries in portable EC meters are often a cause of error.
  • Always take measurements at the same time each day this will allow easier interpretation of the result.
  • Store the meter in a cool dry place.

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