When the mineral elements precipitate, they become insoluble in water, and they need to be water soluble before they can be used by the plants (thus, “tied up” in the nutrient solution). Hydroponic nutrients are made up of both Macro-elements (nutrients that the plants need in large quantities), and Micro-elements (nutrients that the plants need in small quantities). These micro-elements tend to easily bond with the other elements, especially in high pH conditions, and/or when there’s a large concentration of minerals.
What is a Chelated Micro-Nutrient
The Chelating process basically forms a protective shell around the particular mineral element, as well as creates a neutral charge. This keeps them from bonding with each other, and becoming tied up in the nutrient solution. The word “chelate” is of Greek origin and refers to a crabs claw, and the tight hold their claws pinch down with. When two molecules of the same type surround a particular mineral, that’s known as a chelate. But some chelating molecule are shaped like a letter ‘C’ and surround the mineral with just one molecule. This type is called a “complex.” Some minerals like boron are limited to forming only complex bonds, because they only have one chelating molecule they can bond with. This isn’t a true chelated mineral, but it’s often represented and sold as a chelated micro-nutrient.
Types of Chelates
The Chelating molecules need a type of glue to glue them in place to the specific mineral element they want. There’s a few bonding agents that can be used for this, each has a different affect for the plants. The least desirable would be sodium. For anyone who has poured table salt (sodium) on their grass lawn as a kid, knows that sodium is toxic to plants. Along with the mineral elements, the plants will absorb it, and a sodium buildup in the plant tissue could be extremely damaging to the plants.
EDTA
One of the most common forms of chelates is Ethylene Diamine Tetraacetic Acid (EDTA). Ethylene Diamine Tetraacetic Acid is a large synthetic molecule, and it bonds very tightly to mineral elements. But once the elements enters the plant, this very tight bond can be a negative characteristic. The EDTA wants to bond to something so strongly that even once it’s separated from the mineral element inside the plant tissue, it still wants to hold onto something, and so it may grab onto another mineral element. EDTA can help solve one mineral deficiency, but in some cases it can wind up causing another. EDTA has even been known to take calcium directly out of the cell walls of the already formed plant tissue, this causes cell damage to the plant. In cases where there has been a significant amount of cell damage from calcium loss this way, the plant is unable to maintain enough water pressure (like blood pressure in humans), and it may appear like the plants are wilting.
Amino acid Chelates
Another type of chelate is the amino acid chelates. Amino acid chelates have a somewhat less of a strong bond than EDTA chelates, but once the mineral has been absorbed by the plant and released from the amino acid, the plant can also use the left over amino acid as a source of nitrogen. They also have a smaller molecule size than EDTA chelates do. Amino acids are the building blocks for cell formation, so it doesn’t go unused by the plant. Unlike the synthetic EDTA chelates where the plant doesn’t know what to do with it when it’s left over. Because the amino acids are recognized by the plant as building blocks, the minerals can easily move within the plant tissue to where their needed because the leftover amino acids can easily be used anywhere in the plant tissue. Amino acid chelates are also often available for use in organic nutrient formulas, and come in both liquid or dry form.
Glycine Chelates
Another form of amino acid chelates is the glycine chelates. Just like regular amino acid chelates, once the glycine is separated from the mineral element inside the plant tissue, the leftover glycine (amino acid) is used by the plant tissue. The glycine amino acids have an even smaller molecule size, making them even easier to be absorbed by the plants. That makes glycine chelates particularly useful in foliar applications, because they passes through the plants leaf pores (stomata) easier than other, larger molecule chelates can.
Conclusion
Amino acid chelates are very safe for plants, for both root uptake and foliar applications, and would really need large amounts to be applied before they could become toxic to plants. However generally speaking care should be taken to avoid toxic effect using EDTA chelates, and I would always avoid using chelated minerals that use sodium as a binder. When looking for chelated minerals it’s best to look for ones that don’t use sodium, ones that the minerals are readily available to the plants, ones that doesn’t promote other deficiencies (like EDTA chelates), and ones that have an organic certification.
Useful Links
Fertilizer Management for Greenhouse Vegetables
