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What are polyphosphates?

Written by Jaap Lubbersen | Last update: 10-08-2020

Polyphosphates are not commonly known by everyone, in regards to fertilization. Often, the term chelates is mentioned when discussing fertilizers. Chelates are considered an alternative to polyphosphates and are used more often. But what benefits can be named for polyphosphates and what exactly are they?

What is a polyphosphate? 

A polyphosphate can be seen as a row of connections, bound by small acid particles (OH). This phosphate connection is open of structure, meaning it is given the ability to ‘complex’ the molecules. This process of complexing can be compared to a small train. The polyphosphate can be seen as a train, which picks up different molecules along its way. The train will be filled with molecules until every carriage of the train has been filled. 

What is the difference to a chelate? 

A chelate is an organic protein, which is similar to a ‘claw’. In this chelate, the orto-orto concentration is used to indicate by how many ‘arms’ the molecule is held. 

As soon as the chelate has arrived in the root environment, the molecules are released. This because the chelate ‘falls apart’.  After this has happened, all molecules are fully used. Besides this, chelates are only able to bind elements that are positively charged, such as iron, copper, zinc and manganese. Salts cannot be bound to chelates.

A polyphosphate is a connection of phosphate, that complexes molecules. Polyphosphates are able to release the molecules collected, without losing its own structure. This is very different to chelates that need to fall apart in order to release molecules. Because the polyphosphate’s structure remains throughout the process, more molecules can be bound. Molecules, salts and minerals can be bound to polyphosphates, which is called complexing.

Another difference between chelates and polyphosphates can be found in the extra advantage that polyphosphates bring along. 

Why use polyphosphates?

Due to the phosphate connection that a polyphosphate entails, products containing polyphosphates are used to ensure the addition of phosphor

However, another advantage when using polyphosphates can be named. Polyphosphates are known for their cleaning function. This could benefit the dripping pipes, which differs to cleaning the pipes with water. Water does not have the ability to bind molecules, leading to a risk of residue in the pipes. It should be kept in consideration that the phosphate connection cannot bind oxidized forms, such as oxidized iron. 

Not only molecules are bound by polyphosphates outside of the plant, also inside of the plant. Due to this, non-mobile elements are moved through the plant, resulting in the elements not remaining in one place. Calcium can become a mobile element and moved through the entire plant, when bound by a polyphosphate. 

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Application of polyphosphates

It is recommended to make use of a product containing polyphosphates, when a better intake of phosphor is desired. An ‘accidental’ and welcome advantage of this, is the cleaning function. 
It is discouraged to completely replace the addition of phosphorus by means of polyphosphate. The recommended dosage is dependent on the crop, but varies from 0,25 – 1 mmole. When higher dosages than 1 mmole per liter are used, the effects of polyphosphates are barely noticeable.

Tips for use of polyphosphates 

The pH should be kept in mind by making use of polyphosphates. The phosphate connection will release the molecules when the pH range exceeds 7. When the pH range is restored, the structure of the polyphosphate will be repaired automatically, resulting in the possibility to bind molecules again. However, the molecules that were present in the polyphosphate’s structure before falling apart, are lost. In some cases, such as iron, the element is oxidized and therefore not usable for both the plant and the polyphosphate. 

Questions about polyphoasphates

Do you have questions about the usage of polyphosphates or do you want personal advice? Please contact specialist Jaap Lubbersen by filling in the form below. We will contact you as soon as possible, on working days even within 24 hours. 

Jaap Lubbersen About Jaap Lubbersen

Jaap Lubbersen is an internal crop care product specialist at Royal Brinkman and has had over 13 years of experience in glass horticulture. "As an internal product specialist, I deal with growers' issues on a daily basis. Every time again it is a challenge to seek the proper solution, in cooperation with the grower, whether it is about healthy and vibrant cultivation, legislation or safety."

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