What is?

EC is the Electrical Conductivity of a liquid.
The conductivity increases when the content of ions in a liquid is higher. These ions can be from fertilisers (K+, NO32- Ca2+, Mg2+ etc.) or surplus elements like Na+ , Cl , HCO3. So the EC tells you the total concentration of dissolved ions. EC is measured in mS/cm.

EC value can also be given in µS/cm for example; 1 mS/cm = 1000 µS/cm.

The abbreviation of EC = Electrical Conductivity.

pH is a convenient scale for measuring the hydrogen ion concentration in given solutions. Solutions with a pH greater than 7 are basic or alkaline, reflecting a lower hydrogen ion concentration; solutions with a pH less then 7 are acidic. The abbreviation of pH = Product of the H-ions.

Tensiometers are the only instruments that measure directly the suction a plant needs to subtract water from the soil.

A Tensiometer consists of a hollow tube connected to a ceramic tip at the bottom.
A rubber stopper closes the tube at the upper side. The tube has to be filled with demi-water or distilled water. After this the tube has to be placed into the soil. When the soil gets dry it will subtract water from the tube through the ceramic tip. This will cause a vacuum in the tube. When the vacuum is equal to the suction of the soil, the water flow through the ceramic tip will stop. When the soil gets wet through rain or irrigation, the Tensiometer will subtract water from the soil through the ceramic tip caused by the vacuum into the tube. Because of this the vacuum will decrease until it is equal to the soil suction. When the soil is saturated, water can freely flow in and out the tube, so there will be no vacuum into the tube.

In this way we can see the Tensiometer as a synthetic root of a plant where the vacuum is always in balance with the soil suction.
We can use this as a standard for the suction a plant needs to extract water from the soil.

The soilmoisture is measured in hPa.

Main- and trace elements are the nutrients for a vegetation. Main elements are available in higher concentrations and are measured in mmol/l or mg/l (= ppm).
Trace elements are available in lower concentrations and are measured in µmol/l or mg/l (= ppm).

The relative humidity is the moist percentage, which is available in air compared to the maximum moist, which can be contained, by the air (dewpoint). The RH is measured in %.

The abbreviation of RH = Relative Humidity

Lux is the quantity of “visual” light, which falls on a certain surface. Lux gives a total view of all the present light, which can be detected by the human eye.

PAR is the quantity of “grow” light, which falls on a certain surface. A vegetation for photosynthesis uses the “grow” light.