RHP does release test with certified fertilisers

7 april 2023

At the beginning of this year, RHP started an analysis of certified controlled release fertilisers. Our research assistants carry out this release test in our own laboratory. It is a standard check for the RHP quality mark, but this time also intended to gain more insight into the release of the fertilisers as a whole and the nutritional elements separately.

The speed of release is an important feature of controlled release fertilisers. By gaining more insight into the release, a better specification of these fertilisers can be made.

Release test

For this release test, RHP has a specific set-up of incubators and stirrers. The controlled release fertilisers (little balls) go into a bottle with demi-water and are placed in an incubator at a temperature of 25°C.  The water is continuously kept in motion by a magnetic stirrer. At prescribed times, the solution is removed from the bottle and immediately replaced with new demi-water.

Analysis of the solution

The extracted solution is analysed for the content of main and trace elements. With the levels found, the amount of each nutrient element released by the fertiliser can be calculated. With the measuring points in time, the so-called ‘release curve’ can eventually be drawn up.

Research duration

The duration of the release test differs per fertiliser, because it is a ‘real time’ test. A controlled release fertiliser with a specified release of 3 months is therefore actually tested over such a period. But there are also controlled release fertilisers with periods of 6, 9 or even 12 months. These release tests therefore take even longer.

European EN 13266

RHP performs the test  according to EN 13266. This is a European standardised method. RHP uses European  standardised methods as much as possible for analyses, to make sure that test results and also RHP standards are better aligned with the European horticultural sector.

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