Focus on nutritional elements: zinc

28 junE 2018

It is important to add all the nutritional elements in the correct proportion to the substrate to achieve positive instead of negative effects on the culture. Zinc is a micro element that a plant needs in order to grow well. It takes care of the production of the substance that stimulates growth. This time in ‘Focus on nutritional elements’: zinc.

What is the function of zinc?

Zinc (Zn) is part of all the enzymes in the plant. A plant only needs a small quantity of it and it is essential for the production of auxin, the substance that stimulates the growth of the plant. A plant usually takes up zinc as zinc ion (Zn2+), but also in chelate form. A chelate is a compound that can bind itself to a cation. This way it remains in the solution and therefore available to the plant. The word chelate is derived from the Greek word chelate, meaning 'claw'. Zinc is quite mobile in a plant, but this mobility may be decreased by the presence of a large amount of phosphate. The zinc level in the plant usually varies between 0.002 and 0.005 percent of the dry matter.

In which shapes does zinc occur? 

Zinc is added to most potting soil base fertilizers. The behaviour of zinc in a growing medium is relatively normal. However, the phenomenon of chelation can lead to problems. This can happen when the pH in the growing medium increases in the presence of iron chelate. A process occurs during which zinc may suppress iron from the present iron chelate. Zinc that is bound to organic matter, which is not visible in a regular analysis, also contributes to this process. As a consequence, more zinc ends up in the solution and the level of iron decreases. The iron level can decrease so much, that there is barely any noteworthy soluble iron left. It is very difficult to fix such a situation.

Tomato plant with zinc deficiency.

What are the RHP standards for zinc?

Zinc is added to most potting soil base fertilizers. Among other, the zinc levels of RHP certified products are tested before use. There is a maximum level of zinc for growing media with the RHP Horticulture quality mark. Within that norm, the substrate producer and the grower together decide the appropriate zinc level, suiting the culture.

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