Micronutrients such as Fe, Mn, Zn, and Cu are easily oxidized or precipitated in soil, and their utilization is, therefore, not efficient. Chelated fertilisers have been developed to increase micronutrient utilization efficiency. When in chelated form, the metal isn’t precipitated by phosphates, carbonates and other soil and fertiliser components. In this free, chelated form, it remains mobile and unfixed. It is able to move freely through the soil for uptake by the plant root system.
The word chelate is derived from the Greek word chelé, which refers to a lobster’s claw. Hence, chelate refers to the pincer-like way in which a metal nutrient ion like Zinc, Manganese, Iron and Copper is encircled by the larger organic molecule (the claw), usually called a ligand or chelator. Some commonly used chelating agents are EDTA, DTPA, EDDHA, amino acids, organic acids etc. The effectiveness and efficiency of a particular chelated fertiliser depends on the pH of the plant growth medium.
Chelated fertilisers are needed in lesser quantities as they are completely assimiable by crops and hence cost effective. Being organic in nature, they are much more easily absorbed by plant roots or leaves, can be more easily translocated within the plant and assimilated within the plant system. Chelates are compatible with a wide variety of pesticides and liquid fertilisers and are not readily leached from the soil as they adsorb on to the surface of soil particles.