I have had a few discussions recently about starter fertilizers and micronutrients in starter fertilizer blends. Starter fertilizers are a key aspect in getting crops off to a rapid, uniform, aggressive start to the season. I hope that on-farm deliveries of solid starter fertilizer programs- and additional micronutrients like zinc- will fire up across the region very soon. I realized that sometimes we throw around a few terms in discussions that are not necessarily a part of the normal jargon, if you are not an agronomist or sometimes almost a chemist. Chelation is one of those terms. Chelation is an important aspect of keeping micronutrients like zinc in starter fertilizer blends stable and available to the plants, but exactly what chelation is and what it does is maybe a little less clear.
So – chelated micronutrients- what exactly are they- and why should you care? Metal ions like zinc have a positive ionic charge to them. Other primary nutrients in the soil, like phosphorus, exist as negatively charged ionic groups. Opposites attract- and voila- we have a compound made. The problem is that now neither component of the compound is available for plants to utilize in the short term. A chelated micronutrient, on the other hand, is a metal nutrient (zinc, manganese, copper, etc.) with a “coating” on it. This coating has no charge on the outside and many negative electron charges on the “inside” to it- something called “polyvalent”. This coating holds on to the positive charge of the metal ions, which then prevents the metal ions from bonding to things in the soil, and keeps the nutrients available for plant uptake.
Now that coating must be removable, or at least accessible, and that is the “magic” of chelation. The word chelation, derived from the Greek word chele, means claw. The coating on a chelated micronutrient looks something like a claw grabbing the nutrient. The claw does not entirely surround the micronutrient, but protects most of it.
I think of it like a baseball in glove. The ball is captured in the pocket of the glove and protected, but still accessible. Just like there are different sizes of baseball gloves, with micronutrients, we have different chelating agents, and each has a different size “opening” to access the micronutrient. These differences provide different levels of protection to the micronutrient. Not all chelation is equal- weak agents leave large openings, only partially protecting the metal ion. Strong chelators, like EDTA, leave smaller openings and provide more protection to the positive charged micronutrient. Chelation makes nutrients like zinc more available to plants. The difference is dramatic, too- EDTA chelated zinc, like in the SDWG starter additive EnhanZe, is five times more available than ammoniated zinc, which isn’t chelated at all.
Chelation becomes readily noticeable and valuable right from the start- in your mixing tank. Most of our recommended starter fertilizer blends have additives like micronutrients in them. Your starter fertilizer has a lot of things in it the like to react- rapidly or slowly- with micronutrients. Metallic micronutrients with inadequate chelation will react and form visible particles (called precipitants) that settle out of solution to the bottom of the tank, or worse-flow out and plug screens, etc. Regardless, that residue is not available to the plants, even if you can get it applied to the field.
So- the bottom line- maybe you have a little more insight into using chelated micronutrients in starter fertilizers. If you use them, you will be happy with the handling and your plants will be happy with the nutrition available to them. Chelated micronutrients are well worth the investment. Visit with your local Wheat Growers agronomist abut a custom starter fertilizer blend that will meet the nutrient needs of your crops on your farm.