A few weeks ago, I found myself having a discussion about chelated micronutrients. And I’ve been thinking does everyone know what chelation is? It is a chemistry term after all, so it’s not something that I expect everyone to know and understand.
So – chelated micronutrients are a part of our word, which brings us to chelation. I have the mindset that we should only use terms we can define, so in that spirit here’s a little more than a primer on chelation.
A chelated micronutrient is a metal nutrient (iron, zinc, copper, etc.) with a polyvalent coating on it. The polyvalent coating changes the charge of the metal ions from positive to negative, which prevents the metal ions from bonding to things in the soil, thus preserving the ions for uptake by our plants.
The word chelation, derived from the Greek word chele, means claw. The polyvalent coating on a chelated micronutrient is not entirely complete—it has a space in it, which allows for uptake by roots.
How big or small this space is depends on what chelating agent was used and in this detail lies the fact that not all chelated micronutrients are created equally. Weak agents leave large spaces. The metal nutrient is more protected from bonding in the soil than if it weren’t chelated, but not by much. Strong agents, like EDTA, leave smaller spaces and offer much more protection from bonding in the soil.
Consider if you held a golf ball in your open palm. Anyone could walk by and swipe the golf ball from your hand with complete ease. This is the equivalent of an unchelated micronutrient. If you held the golf ball in your palm using your thumb, it would be less available to whomever, but still generally easily grabbed away. This is the equivalent of a weak chelation. If you wrapped all of your fingers around the ball, though, it becomes much less available, and only a very few people might have the strength to take it from you. This, of course, is strong chelation.
Chelation makes nutrients less vulnerable to tie up in the soil and thus more available to our plants. EDTA chelated zinc, for example, is five times more available than ammoniated zinc, which isn’t chelated at all.
An additional benefit of chelation becomes readily apparent in your mixing tank. It’s likely that you’ll be mixing additives in with your starter fertilizer, using solvents that are highly reactive to metals. If you’re using metallic micronutrients with inadequate chelation—and so available for reactions—you’ll create precipitants that will fall out of the mix, collect in the bottom, and plug your screen.
That’s less of the good stuff in your fields, friends, stuck instead on your screen.
Now be rest assured that you can define the terms you’ll be using the next time you find yourself in a discussion about – oh, I don’t know – perhaps whether or not chelated micronutrients are worth the cost.
(Hint: they are.)