Equilibrium reaction between a metallic ion and an organic molecule in which more than one bond links the two components. The metallic ion is termed the complexing agent, the chelating organic molecule the ligand. Chelation is a naturally occurring mechanism in soils, useful since it removes heavy-metal ions that are in solution in simple inorganic form, in which state they may be directly toxic to plants or may interfere with the uptake of essential nutrients. Heavy-metal toxicity will tend to be reduced by the application of organic material.