In order to obtain the right taste, fertilisation is also very important. “A lot of nitrogen gives vegetative growth and is at the expense of the taste,” Verlinden gives an example. The cultivation manager indicates that the company works with “difficult varieties” where problems with blossom end rot are common.

In order to limit the risk of blossom end rot and to optimise the quality of the production, the company was one of the first companies in the Benelux to start using Ambiorix, a liquid iron polyphosphate, as an alternative fertiliser for iron chelate a year and a half ago. “Iron polyphosphate ensures a better transfer of calcium, which can prevent blossom end rot,” says Verlinden.

Polyphosphates, on the other hand, are inorganic substances that do not contain carbon and therefore oxidise less easily when they come into contact with disinfectants. Prayon and Roam Technology closely monitored the cultivation at Stoffels last year by analysing the irrigation and drainage water in combination with weekly plant sap analyses.

According to Pinxteren, this clearly shows that the iron is hardly broken down in combination with a disinfectant and the iron supply is much more stable. The absorption of other elements, such as calcium, zinc, manganese and copper, is also better. “The polyphosphates (negatively charged) also complex other 2-valent positive nutrients, which means that they are, as it were, carried along with the polyphosphates, straight to the roots,” it sounds.

Together with Prayon, Roam Technology managed to get a foot in the door with ten vegetable growers in the Netherlands and Belgium in the short term, including lettuce growers, eggplant growers, cucumber growers and tomato growers. In this last group, companies that focus on the production of varieties susceptible to blossom end rot are the frontrunners. Another interesting factor for lettuce growers is that the carbon filters become less clogged. “These filters stop the organic chelates, while allowing inorganic polyphosphates to pass through,” Pinxteren explains.

The former researcher at Proefcentrum Hoogstraten (a Belgian practice-oriented research centre in horticulture) indicates that the collaboration with growers proceeds in steps, with companies often stepping in cautiously. Not surprising, says Staf Verlinden, who also started with a limited trial. “Growers are often cautious and want hard evidence and guarantees before they switch. A change of mentality is often also necessary.

For fear of too low an iron content, Verlinden added a larger dose of iron chelate for years to compensate for any breakdown of iron. “An extra dose of iron chelates has no adverse effects and offers certainty,” he explains. Pinxteren sees this at many more greenhouse horticulture companies where the iron dose is sometimes even many times higher than the required minimum of 15 micromol per liter.

“By using polyphosphates, we can reduce our iron use. That also means savings,” says Verlinden, who looks back with satisfaction on the partial switch to the new iron fertiliser.

The tomato company is considering expanding the current area of ​​5.5 hectares on which Ambiorix is used. “Last year we had a good, high-quality season without blossom end rot. It is of course a combination of factors, but the use of Ambiorix certainly played a role,” says Verlinden.

Since using Ambiorix, Stoffels has reduced the standard addition of iron from 70 micromol to 50 micromol per liter. “In the long term, we think we can reduce this dose to 35 micromol per liter,” concludes the cultivation manager.

(as published in Dutch magazine “Onder Glas”, 16 May 2024)