Chelated Zinc Fertilizers

So, you got your soil test results back and it recommended and application of a micronutrient such as copper, iron, manganese or zinc. Now it’s time to pick a product. You’ll likely notice that there are many options and many different price points for the same amount of fertilizer. Why is this? There are several factors at play here, but after inspecting the labels of these fertilizers a bit closer you’ll likely recognize that some may contain, for example, Zinc Sulfate, while others may contain Zinc EDTA, Zinc DTPA, Zinc EDTA & IDS, or Zinc EDDHA and so on. The last four listed indicate that the zinc is coupled with a chelating agent, or in other words, that the zinc is chelated. The word ‘chelate’ is derived from the Greek word for claw or lobster claw. What is the difference between a nutrient that is chelated and one that isn’t? In the case of Zinc and many other micronutrients, once applied to soil in their elemental form they are susceptible to being fixed, or made unavailable, by different chemical and biological processes. A great example is that when Zinc is applied to soils with pH greater that 6.5, especially those higher than 7.0, it is susceptible to being fixed by phosphate, making it unavailable. When Zinc Sulfate is added to the soil, the following reactions are likely to occur, making some of the applied zinc unavailable for plant uptake.