EC and plant growth

Optimal growth and plant quality need sometimes a high and sometimes a low EC!

Introduction

The EC (mS/cm) is the electric conductivity of the substrate and in this way the amount of feeding elements around the roots is measured. With the amount of feeding plant growth can be
influenced. In practice growers can regulate plant growth and quality with the EC, soil or substrate moisture and RH.

EC and feeding elements

Every plant variety has its own characteristic feeding solution. The balance between the elements depends on the way of growing whether the plant makes leaves, flowers or fruits.
The EC level depends on the growth speed of the plants. In case of fast growing crops and a good climate the feeding should be higher. The grower self has to judge if the plant needs more or less. Rinsing with clean water can even be necessary.

High EC

A high EC reduces the uptake of water and so the cell stretching of the growing point is inhibited. This is the real salt effect. A higher EC causes a higher risk for a too salty substrate and so root dying. The EC of the plant sap has an EC around 12 to 14 mS/cm. In case the EC in the substrate becomes that high a process with the name plasmolysis can
happen. In that situation water is drawn out of the plant cells towards the salt in the substrate. A high EC can in this way damage the roots. In de pot plant culture a high sulphate is added
because this element increases the EC but does not stimulate growth and in this way plants stay smaller.

Low EC

AT a low EC plants get to little to grow. In fact is this a deficiency of 1 element. The elements which are most often used to influence growth and are not causing mis forming are nitrogen en phosphate. A low phosphate dosage is used in the bedding plant cultivation to keep plants compact. At a low nitrogen level plants stay smaller. Higher amounts of nitrogen causes a more vegetative growth and stimulates leave size. In generative feeding schemes nitrogen is reduced for this reason and in this way the plant is stimulated to stop growing and form flowers. Low nitrogen can cause plants to flower earlier. Low nitrogen in the beginning of growth keeps the plant smaller. The flower size is bigger when more nitrogen is applied.

EC and watering

A dry substrate has a higher EC. A normal moistures substrate has for instance an EC of 1.5 mS/cm, when this substrate becomes dryer the EC can go up till 3.5mS/cm. This difference in EC is also present between wet and dry spots in soil or in a slab. In practical situations the EC at the driest places can be 3 till 4 times higher as the measured EC.
In pot plants experiments are done with increasing EC levels. In Asplenium plants stay smaller at a low EC of 0.3. At a EC of 1.2 plants become much bigger and the colour is darker green.

EC and evaporation

The upward flow of water also transports the feeding elements. With a higher flow of water also
more feeding elements are transported to the leaves. Some of the salts like sodium and boron are taken up more than necessary. The concentration on these elements is in the leave edge and tips always highest. This is in fact a kind of self defense of the plant. In case the salt content becomes too high the leave tip dies and in this way the plant discarded the surplus of salts. Other plants have special openings at the leave edge and salt is pushed out by the process of guttation.
In summer time a plant evaporates more to cool itself than in wintertime. The water used for cooling is extra above the normal amount of water to transport the elements. For that reason in summer time an EC reduction of 0.3-0.5 is programmed during high irradiation and the warmest period of the day.
The EC level is the quantity of food that is provided to the plant. In case of a low EC the plant cannot eat enough and stays thin. With a high EC the plant gets too much and this also inhibits growth. For that reason it is important to measure the EC regularly on several locations in the greenhouse.

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