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  • 11-04-2023

Complexes and chelates: Differences in action and use

Within plant nutrition there are micronutrients and macronutrients, which are named according to the amount the plant needs. In spite of these names, neither is more important than the other, because as Liebig’s law of the minimum says, a nutrient that is not supplied in the right amount limits growth.

Micronutrients are mainly metallic elements, and the vast majority of problems resulting from a lack of micronutrients come from a lack of absorbable forms of ions from those metals, which plants are not able to absorb and incorporate into their metabolism.

To facilitate these processes, formulations can be used with complexed or chelated micronutrients, which are absorption enhancers, molecules that bind with metal ions and prevent them from precipitating in the form of an insoluble salt in order to facilitate their absorption. The use of these compounds allows us to reduce the amount of nutrients applied, thanks to an improved absorption by the plant and a reduction in nutrient leaching.

Although we always mention chelates and complexes together, these molecules are different, both at a chemical level and in their application method:

  • Chelates have the ability to bind metal ions much more strongly and with a higher stable pH range. They are also larger molecules than complexes. In terms of use, they are particularly effective when used at root level, because once they release the nutrient to which they are bound, they can also chelate metals already in the soil.
  • Complexes have a weaker binding which facilitates the release of nutrients for plant uptake and have a somewhat more limited pH range of use. They are organic molecules (e.g. lignosulphonates, gluconic or heptagluconic acid, humic substances, amino acids, citric acid…) and can have a biostimulant effect on the plant. They are also biodegradable. They are especially good in foliar application, as the high absorption rate per leaf makes the complexing agents enter the plant faster.

As shown in Illustration 1, each chelate will have a wider or narrower range of stability depending on the micronutrient to which it is bound. Therefore, the choice of the best chelating agent will depend on the conditions of our soil and the micronutrient we want to supply.

One of the most common chelating agents is EDTA, whose use is quite common for chelating manganese (Mn), zinc (Zn) and copper (Cu), as it has a wide pH range for them. In the case of iron (Fe), EDTA is less available, so it is better to use higher quality molecules, such as EDDHA or EDDHSA. EDDHSA is an improved agent because it ensures the ortho-ortho conformation of the molecule, which is more effective and biologically active.

At Herogra Especiales, we have a wide range of both complexed and chelated products, many of them certified for use in organic farming.

Our experts recommend  FERROLÍN EDDHSA, a solid iron deficiency corrector with high solubility and efficacy thanks to the quality of its chelating agent. Some nutrients cannot be chelated or complexed, such as boron or molybdenum.

HEROMIX COMPLEX T1 is a multiple micronutrient corrector complexed with heptagluconic acid, specially designed to improve plant uptake. In order to correct calcium or magnesium deficiencies, we can use products such as CALCIFOL PLUS SN or MAGNIFOL COMPLEX, specialized products for specific deficiencies in which nutrients are complexed with lignosulphonic acid.

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