Different types of chelating agents are used with the Akzo Nobel product range. These are designated EDDHMA, EDDHA, HEDTA, DTPA and EDTA. The type of chelating agent recommended depends mainly on the method of application, the crop, and the pH value of the soil or other growth media. The active pH ranges of the products are shown in figures 1 and 2. It is the sensitivity to the pH of the iron-chelates which has necessitated the broad product range for Fe. For all other metals i.e. Ca, Cu, Mg, Mn and Zn mainly EDTA is used.

For foliar application invariably EDTA is used as a chelating agent for all trace elements including iron. In hard water areas, Fe-DTPA is recommended.

In soil application EDDHA and EDDHMA are the preferable chelating agents for ensuring iron availability in alkaline soils. Iron chelates of HEDTA, DTPA and EDTA are also effective in less alkaline or acidic soils (see figure 1). For the other trace elements EDTA is the most common chelating agent (see figure 2).