Introduction
Certain chemical elements, known as nutrients, play a fundamental role in the growth and viability of crops. These have to be provided in sufficient quantity to have a healthy crop. There are several ways to provide nutrients: inorganic form, in the form of complexes or in the form of chelates. In the case of the last two forms, these are nutrients “sequestered” by molecules (or agents) that facilitate their incorporation into the plant and greatly increase the availability of these nutrients for plants.
In this report we analyze the advantages of complexes / chelates as a way of applying nutrients to inorganic forms and how to choose if chelates or complexes are required.
Technical information: chelates vs complexes
Nutrients
Some chemical elements play an important role in all living beings. They are known as Nutrients.
They are divided into four groups:
- CHO elements: Acronym for Carbon, Hydrogen, and Oxygen. They are the major elements in all living beings.
- Macroelements: Elements that are found in large quantities in plants. They are key for their survival. Nitrogen, Potassium and Phosphorus are included here.
- Secondary macroelements: Macroelements presents in lower concentrations that the primaries. Sulphur (S), Calcium (Ca) and Magnesium (Mg)are included here.
- Microelements: Nutrients present in plants in really low concentrations. Chlorine (Cl), Iron (Fe), Boron (B), Manganese (Mn), Zinc (Zn), Copper (Cu), Molybdenum (Mo) and Nickel (Ni) are included here.
Nutrient Application
To avoid or correct a deficiency of the mentioned nutrients crops are applied:
Mineral Compounds
They are natural minerals: oxides, nitrates, chlorides and sulphates. The widest used compounds are sulphates and nitrates. These elements, since they are solo, they can react freely with soil ions, making them precipitate.
Complexes vs Chelates
Nutrients attached to a molecule that avoid them precipitating as an inorganic salt and makes their assimilation by the plant easier. There are two kinds of molecules, or agents: Complexing or Chelating agents.
Chelating vs Complexing Agents
An agent is the molecule with the ability to attach itself to elements with an ionic valence of +2 or +3. We classify them into complexing or chelating agents, and from natural or synthetic origin.
Chelates
Chelating agents are molecules with the ability to attach to nutrients (Zn, Cu…) forming VERY STABLE bonds. They are all synthetics. The most common agents are EDTA, HEDTA and EDDHA. They are not biodegradables, so they leave residues in the ground.
Complexes
Complexing agents are molecules from synthetic and natural origin that form less stable bonds with nutrients than the chelating agents. In return, they are fully biodegradable and easier to produce.
Among synthetic complexing agent we find gluconic and heptagluconic acids, and among the natural ones, lignosulphonates, amino acids, reducing sugars, humic and fulvic matters…
Chelating
EDTA
This is the most widespread agent in the market, and it is used along all microelements. It shows a higher affinity (chelating constant) slightly superior to HEDTA
HEDTA
This chelating agent is similar but different to EDTA. It shows less affinity for some microelements than EDTA, but its extra Hydrogen makes these compounds more water-soluble and less photosensible, making them more suitable as foliar application products than EDTA chelates.
Complexes (synthesis)
Gluconic Acid
This complexing agent shows a good affinity for ions, but this affinity is lower than any chelating agent. It is a completely biodegradable agent, leaving no residues in the soil.
Heptagluconic Acid
This complexing agent is similar to the gluconic acid but it has more anchoring points, and a single agent can complex several nutrients. Also it shows great affinity for nutrients at basic pH, making it suitable as a complexing agent in limestone soils.
Complexes (organic)
Lignosulphonates
These compounds, extracted from wood, are completely natural, so besides its complexing power they act as organic matter when they are applied. They are fully biodegradable and complex macro and microelements.
Boron and Molybdenum
Both Boron and Molybdenum cannot be chelated/complexed because of their ionic valence. Their application is exclusively mineral.
Boron is often reacted with ethanolamine, producing the compound Boroethanolamine that improves the formulation of Boron-containing products since they increase the quantity of Boron that can be solved in the formula.
