Focus on nutritional elements: sodium and chloride 

31 january 2019

This edition of ‘Focus on nutritional elements’: everything about sodium and chloride, also referred to as ballast salts. Apart from the main and trace elements that were discussed earlier in this section, an element to take into account in substrates and cultures.

What is the function of sodium and chloride?

There are a couple of elements that aren’t mentioned in the ‘standard list’, but still play a part in the growth of plants. Chloride (Cl) for example, is regarded as a trace element. It is required for the growth of plants. Normal (small) amounts of sodium (Na) are known to have a positive effect on the water management of the plant. High concentrations in substrates are harmful to plants.

In what shapes do sodium and chloride occur?

When it comes to fertilizing, sodium and chloride are not regarded as nutritional elements. Active fertilizing with chloride is not necessary, because the plant naturally has it at its disposal from the substrate, the water and even from the atmosphere. Fertilizers can also contain sodium and chloride. Horticulture fertilizers as a rule contain no or very little sodium and chloride. Unprocessed coir dust contains many salts, including sodium and chloride. This is expressed in a high up to a very high EC and, among others, a high sodium level in watery extracts. This is the most important reason to process coir products. Compost can also contain relatively a lot of sodium, therefore it can only be mixed in substrates up to a certain level. Apart from that, the water that the grower uses for the culture can also contain sodium and chloride.

What is the effect of sodium and chloride?

In high concentrations, sodium and chloride are harmful for the crop. This is often called salt damage, which in the crop leads to scorching of the edges of the leaves. High levels of sodium and/or chloride slow down the uptake of nutritional elements that the plant needs in order to develop. The water quality and the use of fertilizers during the culture lead to the highest build-up of sodium and chloride. For most potted plants sodium and chloride levels of 2,0 mmol/l are no problem. Recently WUR Greenhouse Horticulture reported that many crops can handle higher levels without any problems. Therefore disposing of nutrition water isn’t necessary as often as people think. Partially because of that, aiming for extremely low levels of sodium and chloride in freshly produced substrates is not necessary.

What are the RHP requirements of sodium and chloride?

Sodium and chloride are not added specifically to potting soil base fertilizers. It is, however, important to take into account a possibly (excessive) presence of it in substrates. RHP sets quality requirements for among others, the EC-value of substrates and the maximum level of sodium and chloride in substrates.

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