What are chelated micronutrients?
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Chelated micronutrients are iron, manganese, zinc or copper held in a ring structure by a chelating molecule, which keeps the metal soluble and protected from precipitation until the plant takes it up. They matter most in neutral to alkaline soils, where iron precipitates above about pH 7 and a crop can show severe chlorosis even though the soil holds abundant iron.
What problem does chelation solve?
Iron, manganese, zinc and copper are essential micronutrients, and in neutral to alkaline soils they are largely unavailable - iron in particular precipitates as insoluble hydroxides and oxides above about pH 7. A soil can contain abundant iron while the crop shows severe chlorosis. Applying iron sulfate to such a soil often fails, because the iron precipitates before it reaches the root.
A chelate is a molecule that binds a metal ion in a ring structure, keeping it soluble and protected from precipitation until it reaches the plant, where it is released.
Which chelate works at which pH?
EDTA is the most common and the one used in this range, as EDTA-Fe. It is effective and inexpensive but its stability falls away above roughly pH 6.5, so in strongly alkaline soils it releases iron prematurely.
DTPA is stable to around pH 7.5, and EDDHA to pH 9 and above - which is why EDDHA is the standard choice for calcareous soils despite its higher cost. A product formulated with EDTA-Fe is well suited to acid and neutral conditions and less so to high-pH soils, and that is useful, specific information for a grower.
Amino acid and organic acid chelates - citrate, gluconate, and amino-acid complexes - are weaker but genuinely useful for foliar application, where soil chemistry is not the constraint and lower molecular weight aids uptake. Several products in the range use citric acid and glutamic acid in this role.
Is a chelate natural?
EDTA is a synthetic aminopolycarboxylic acid. It is not naturally derived, it is poorly biodegradable, and it is persistent enough in water to have attracted environmental attention as a mobilizer of metals in aquatic systems. Describing an EDTA-chelated product as naturally derived is not defensible.
Natural chelation does exist · plants secrete siderophores and organic acids to mobilize iron, and amino acid and citrate complexes mimic that. Those are the natural analogues, and they are weaker. A product range positioned around natural inputs is better served by explaining that trade-off honestly than by blurring it, and this page is where that explanation belongs.
What does chelated micronutrients not do?
They do not add micronutrients that are absent, only make present ones available. They do not work outside their pH stability range. And over-application of strong chelates can mobilize unwanted metals as readily as wanted ones.
Where does chelated micronutrients appear in the range?
EDTA-Fe appears in Micro Boost, Nitrogen Pro, NPK Pro and Vega Pro. Micro Boost also uses glutamic and citric acids, and most products in the range include citric acid.
Key takeaways
- Iron sulfate applied to alkaline soil often fails because the iron precipitates before it reaches the root.
- EDTA stability falls away above roughly pH 6.5; DTPA is stable to around pH 7.5 and EDDHA to pH 9 and above.
- EDDHA is the standard choice for calcareous soils despite its higher cost.
- Amino acid and citrate chelates are weaker but useful for foliar application.
- Chelates do not add absent micronutrients; they make present ones available.
References
Frequently asked questions
What is the difference between EDTA, DTPA and EDDHA?
The main difference is the pH range over which each holds its metal. EDTA is the most common and inexpensive, but its stability falls away above roughly pH 6.5. DTPA is stable to around pH 7.5, and EDDHA to pH 9 and above, which is why EDDHA is standard for calcareous soils despite its cost.
When should you use chelated iron?
Chelated iron makes sense where soil pH keeps iron unavailable, so the crop shows chlorosis although the soil contains iron. Match the chelate to the soil: EDTA-Fe suits acid and neutral conditions, while strongly alkaline soils need a chelate that stays stable at higher pH. Chelates do not work outside their stability range.
Which chelates suit foliar sprays?
Amino acid and organic acid chelates, such as citrate, gluconate and amino-acid complexes, are weaker but genuinely useful for foliar application. On the leaf, soil chemistry is not the constraint, and their lower molecular weight aids uptake.
Related reading
Products
No direct product mapping. Nothing in the Vegalab range declares chelated micronutrients in its composition, so this page has no product link - the absence is deliberate, not an omission.