Metal chelate compounds are common components of fertilizers to provide micronutrients.  These micronutrients (manganese, iron, zinc, copper) are required for the health of the plants.  Most fertilizers contain phosphate salts that, in the absence of chelating agents, typically convert these metal ions into insoluble solids that are of no nutritional value to the plants.  EDTA is the typical chelating agent that keeps these metal ions in a soluble form.