What is EC?
Electrical conductivity or “EC” is a measure of the concentration of “total salt” in a nutrient solution (drip, plate or drain).
It is expressed as milliSiemens per linear centimeter (mS/cm) or microSiemens per linear centimeter (mS/cm), where 1mS = 1000µS. The conductivity of a given solution varies with temperature, so most nutrient solution analyses are performed at 20oC.
The higher the concentration of “total salt” in the substrate, the higher the EC. Inorganic fertilizer ions such as N, P, K, Ca, Mg, etc. are examples. Urea is an organic molecule and will not contribute to the EC of the solution because it does not conduct electricity like calcium (Ca) ions or nitrates. Nitrogen (NO3-N) ions can.
The EC required for optimal plant growth depends on the crop and variety grown, the physiological stage of plant development and the prevailing environmental conditions inside and outside the greenhouse.
Why is it important to monitor EC?
The EC of the nutrient solution affects the growth and development of the plant. In the winter, higher EC is used because it limits water uptake. As a result, the cells in the plant do not elongate or “grow” too much. They stay smaller and have thicker, stronger cell walls. The plants then look darker, shorter and have smaller leaves. In this case, the plant puts relatively more energy into the formation of flowers and fruits (a production reaction). If the EC is too low under poor light conditions (i.e. winter), the plant will produce too much leaf growth and too little fruit growth, and will therefore be over-nourished.
Conversely, high EC under high light conditions (summer) will restrict water uptake too much and thus limit the plant’s ability to cool itself through transpiration. As a result, the crop will be stressed.
EC also affects yield and fruit quality. In general, higher EC in the root zone environment leads to lower yields and smaller fruit size. This is because the cells in the fruit absorb less water, resulting in lower fresh weight. However, higher EC leads to better fruit flavor. Therefore, a compromise must be made between fruit quality, yield, and the nutritional and reproductive development of the crop.
Therefore, it is important to maintain the correct EC in the root zone environment (measured as the difference between slab EC and drip EC.) The value of EC varies for each crop type and time of year.
Monitoring EC in the slab
Monitoring EC in plates is an important component of weekly nutrition monitoring and should be performed daily. For a meaningful and accurate assessment, sampling should be performed in multiple representative plates. Sampling is easy by simply pushing a syringe into the plate and withdrawing a small amount of nutrient solution (100 ml), which is then placed into the cup of the EC meter for direct reading. The EC values are calculated and plotted on a graph so that trends can be more easily identified.
Tips for accurate EC measurements with portable meters
- Calibrate the EC meter periodically using a standard solution.
- Check the battery status, low battery in portable EC meters is often the cause of errors.
- Take measurements at the same time each day so that results can be interpreted more easily.
- Store the meter in a cool, dry place.