Christopher C. Underwood, Ph.D.
Chemist / Product Development Manager
Chelates…chelation…chelated products. The use of common chelants, such as EDTA and EDDHA, has been long-debated in crop fertility. Which one(s) keep a micronutrient from reacting with other materials in a blend, while allowing for plant uptake once in the soil? Companies that use these technologies claim that their chelation prevents micronutrient tie-up in the soil and allow for better plant uptake. While most of these claims are true, some chelants are better than others. First, it’s helpful to understand what a chelation actually is.
What is chelation? Think of chelates like Russian nesting dolls or the AgroLiquid football player inside a bubble ball: the smallest doll is put inside a slightly larger doll and so on and so forth. The smaller dolls are completely encapsulated by a larger doll. Now think of a micronutrient like the smaller doll and the chelant like the larger doll. In essence, a chelant attempts to encapsulate the micronutrient. For instance, one EDTA molecule has the ability to completely encapsulate a micronutrient. There are other, smaller chelants that require two or three molecules (like amino acids) to encapsulate a micronutrient.
The rub: Once a chelated nutrient is applied, whether in the soil or as a foliar, the trick is to remove the chelant to allow the plant to utilize the nutrient. There are a few factors to consider…
Common chelants are most effective in a small pH window. EDTA, the most commonly-used chelant, can best keep nutrients chelated when the soil pH is between 5 to 7. EDDHA is normally used when the soil pH is over 7.5. Amino acids and citrates are best in soils with acidic pH (pH<7) but are not effective chelants in the soil.
Common chelants have variable binding to micronutrients. Some chelants do not encapsulate nutrients as tightly as others. Some chelants, like EDTA and EDDHA, hold the nutrient so tightly that only a few mechanisms (like a select few soil bacteria or a couple of plant processes) can break it down and allow the plant to use it. Other chelants, like amino acids and citrates, hold so loosely that other compounds (like soil phosphate, for example) can displace the chelant and tie up the nutrient. The ideal chelant follows the “Goldilocks Principle”: it holds the nutrient strongly enough to keep other compounds from reacting with it, but loosely enough to be freed from encapsulation so that it can be used by the plant.
Common chelants can have adverse effects on soil health. Some common chelants, such as EDTA and EDDHA, do not break down quickly in the soil. As of now, there are only a few known strains of bacteria that can break down these chelants. Most usually leach through the soil profile before they are broken down, causing possible long-term environmental concerns. Before they break down, they also have the ability to chelate other heavy metals in the soil, such as lead, aluminum, and cadmium, and (here’s the real kicker) can make those heavy metals more available to the plant! They are also harmful to beneficial nitrogen-fixing bacteria such as Azotobacter spp. and Rhizobium spp.
As a foliar, they are somewhat efficient at penetrating the waxy cuticle of a leaf but still rely on multiple biological pathways to break down the chelant before it can be used by the plant. Other natural product-based chelants, such as amino acids or citrates, can also achieve cuticle penetration but can only be made in low concentrations due to their water solubility (sometimes not at all).
Choose the right chelation! The chelation technology we use at AgroLiquid utilizes a flavanol-based polymer derived from a natural source. This allows us to chelate micronutrients within the sweet spot of the Goldilocks Principle (not too loosely but not too tightly). The same flavanol-based polymer also makes our products effective foliars, as it is efficient at penetrating the leaf cuticle. Since our chelation is derived from natural sources, it can (1) be broken down over time by soil biology without the worry of adverse effects in soil applications, and (2) be quickly broken down by the plant and used as other metabolites in foliar applications.