IRON CHELATE: CHARACTERISTICS, TYPES, PROPERTIES, DOSAGE - BIOLOGY - 2025

An iron chelate is a complex formed by the union of an iron atom and a compound that contains two or more molecules of cyclic structure. The term "chelate" derives from the Greek "χηλή, chēlē" which means "clamp", due to the clamp-like shape of the ring that forms between the chelator and the metal.

Iron chelates are products widely used in agriculture, since their application prevents iron deficiency in many crops of commercial interest. Iron is a key mineral compound in the metabolism of plants and is vital for their development.

Chlorosis in Capsicum annuum leaves. Source: Dacnoh / CC BY-SA (https://creativecommons.org/licenses/by-sa/3.0)

Iron is a constituent element of various enzymes and certain plant pigments, essential for the production of chlorophyll and a necessary cofactor for multiple metabolic processes. In addition, it allows regulating the levels of nitrates and nitrites, as well as increasing energy production in the respiration process of the plant.

Although iron is not used directly in the synthesis of chlorophyll, its presence is essential to complete the process. Hence its deficiency in plants manifests as intravenous chlorosis of new leaves.

In fact, soils have a high content of iron, but its availability to plants is very low. Hence, iron deficiency is very common in plants, being one of the main limiting factors in the production of cereals, vegetables, fruit trees and ornamentals.

Iron chelate characteristics

On a commercial level, iron chelate is a water soluble microgranulate. Its application not only has a positive effect on plants, but it also allows correcting the pH levels of the soil.

The iron chelate is applied as an edaphic or foliar fertilizer to prevent and correct iron deficiency or iron chlorosis. This mineral deficit is manifested as a yellowing of the foliage, due to the low production of chlorophyll in the new leaves of the plant.

External factors such as the type of soil, excess humidity, high pH, ​​substrate temperature and presence of nematodes, exacerbate iron chlorosis. In the same way, the plant tends to slow down its growth and the size of the fruits is smaller than normal.

When the leaves of a crop begin to show iron deficiency, the application of iron does not solve the problem, the application of iron chelates does. Chelates are soluble, easy for the plant to absorb, and tend to stay longer in the soil.

Types

Chelates are compounds that stabilize iron ions, preventing their oxidation and subsequent precipitation. Iron chelates are made up of three components:

- Ions of Fe ³⁺

- A complex, which can be EDTA, DTPA, EDDHA, humic or fulvic acids, amino acids or citrate.

- Sodium (Na ⁺) or ammonium (NH4 ⁺) ions

Chelates vary in their strength and stability under different pH levels. Furthermore, they are susceptible to iron ion displacement by various competitive ions, such as calcium or magnesium ions that can displace iron from the chelate.

Lemon leaf without yellowing symptoms. Source: pixabay.com

Among the types of chelates most used commercially, we can mention:

EDDHA

Known as ethylenediamino-di (o-hydroxyphenyl-acetic acid), they are the most widely used chelates on the market, as they have high stability and are very effective in the long term. Under certain circumstances, they are less stable, but they respond more quickly by making up for iron deficiency. Contains 6% iron.

EDDHMA, EDDHSA and EEDCHA

The most common is ethylenediamine-N, N′-bis, they are chelates of excellent stability. EDDHSA and EEDCHA are used as liquid fertilizers for foliar application due to their high solubility.

EDTA, HEEDTA and DTPA

Known as ethylene-diamine-tetraacetic acid, hydroxy-ethylethylene-diamine-triacetic acid, and pentetic acid, they are not very stable compounds. However, they are used in crops that are not very sensitive to the symptoms of chlorosis.

EDTA is stable at a pH lower than 6.0, in soils with a pH higher than 6.5 the availability of iron is reduced to more than 50%. On the other hand, DTPA is only stable in soils with pH values ​​lower than 7.0. EDTA contains 13% iron and DTPA 10%.

What is the iron chelate for?

Iron chelates are used to supply the iron deficiency in any type of crop, be it vegetables, cereals, fodder, ornamental or fruit. Iron is one of the main micronutrients that plants require to grow and develop properly.

Plants generally show symptoms of iron deficiency, due to their low solubility in the soil or the great susceptibility of plants to this element. The main problems associated with iron deficiency occur in alkaline soils where iron is not available to the plant.

The main symptom associated with iron deficiency is iron chlorosis, characterized by yellowing between the nerves of young leaves. The frequent expansion of iron chelates solves this nutritional deficit since micronutrients dissolve more easily in the soil.

Properties

- Great water solubility capacity, which favors its absorption through the root system or leaf area.

- It is very resistant to biotransformation, which allows it to exert its function in the leaves without suffering any type of degradation along the way.

- It has the ability to overcome the various chemical and physical barriers of plant organisms to reach the area where it performs its function.

- It is able to render useless the toxicity of certain heavy metals, forming non-toxic complexes from toxic metals, such as iron.

- They maintain their chelating activity under different pH levels of soils or substrates.

- They have an excellent affinity and specificity on heavy metals.

Foliar application of microelements. Source: pixabay.com

Dose

The recommended dose, regardless of the type of iron chelate used, is 40-50 grams of iron chelate for each liter of water, and injected at a ratio of 1: 100. This dose allows the application of 35-45 ppm of iron to the culture with symptoms of iron chlorosis.

It is important to follow the following guidelines to obtain the best results:

- Apply on the soil or dry substrate, wetting the soil around the plant well, in order to maximize its absorption.

- Foliar applications are made in the first leaves in the morning, then sprinkler irrigation is applied to prevent the appearance of spots or burning of the foliage.

- The iron chelate based on Fe-EDDHA is very effective, depending on the permeability of the soil and its pH range, its application can be done every 30 days.

- In iron chelate based on Fe-DTPA, little remains in the soil, so more frequent applications are required.

- Store iron chelates and solution mixtures in a cool, dark place, since solar radiation tends to degrade chelates.

- Soils with high or alkaline pH require amendment with potentially acidic fertilizers or correction with acid solutions.

- The application of iron is carried out at the beginning of the productive phase, in order to guarantee good sprouting, flowering and fruit set.

- Depending on the degree of yellowing or chlorosis of the crop, the application of chelates can be carried out throughout the vegetative cycle.

References

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5. Lucena, JJ (2018) The Quality of Iron Chelates in the National Market. Recovered at: infoagro.com
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7. Villaverde, J. (2016) Iron chelates for iron chlorosis. Plantamus: Nursery Online. Recovered in: plantamus.com