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Iron-polyphosphate fertiliser, alternative for iron-chelate

Gepubliceerd op
7 januari 2014

Ions of Fe will precipitate easily in nutrient solutions, therefore chelates are used to make this nutrient available for plants. Prayon, producer of phosphate fertilizers developed an alternative in form of a polyphosphate. Trials at WUR in Bleiswijk showed that this fertilizer can be used in soil-less culture.

Ions of Fe will precipitate easily in nutrient solutions, therefore chelates are used to make this nutrient available for plants. Prayon, producer of phosphate fertilizers developed an alternative in form of a polyphosphate. Trials at WUR in Bleiswijk showed that this fertilizer can be used in soil-less culture.

Two short trials were performed to compare several forms of Fe-polyphosphates with DTPA. Cucumber was used as test crop, with low pH (5.2 – 5.8) and high pH (6.4 – 6.8), with 25 and 15 µmol l-1 in the 1st and 2nd trial respectively. In the 1st trial, no significant differences could be observed between the treatments. In the 2nd trial (the low Fe concentration), the growth was much reduced at the high pH treatments, especially with the Fe-polyphosphates. This coincided with severe chlorosis at the high pH treatments. The Fe-uptake was notably higher at the Fe-polyphosphate treatments compared with DTPA. 

The investigation was continued with a trial on semi-commercial scale with cucumber in rockwool. The pH was kept between 5.5 and 6. The results confirmed those of the initial trials.

Improvement of Ca uptake?

Notably, there was a significant difference in the occurrence of tipburn or cupped leaf (associated with Ca deficiency), which was severe at the DTPA treatments and almost non exisiting at the Fe-polyphosphate treatments. As indicated elsewhere as well, polyphosphates might be able to promote Ca uptake or transport. This needs further investigations.

The new Fe-fertiliser will be a useful addition to the set of Fe fertilisers, in particular in view of the benefit on Ca. However, high pH levels need to be avoided

The incidence of chlorosis  was more severe at high pH and Fe-polyphosphate
The incidence of chlorosis was more severe at high pH and Fe-polyphosphate
Tipburn and leaf cupping occurred at the DTPA treatments
Tipburn and leaf cupping occurred at the DTPA treatments