WHAT is CHELATE?
Iron chelate is a complex that gives the metal ion more stability. A chelate protects a metal ion from early precipitation (oxidizing).
A chelate contains 3 components:
- Fe3+ ,
- complex part (EDTA, DTPA, EDDHA, amino-acid, humic – fulvic acids, citrate),
added ion (Na+ or NH4+)
In order to have a strong and complete chelate to avoid precipitation, it should be completely chelated.
Absorption of Iron Chelate
In strategy I pH is lowered by the excretion of protons (provided by an ATPase associated with the plasma membrane) and the Fe3+ is separated from the chelate agent and lowered to Fe2+ to absorb it in the plant. After in the plant the iron is formed to Fe3+ and transported the upper plant via Xylem.
Stability of the Chelate
Metal chelates - chemical stability:
Above is shown that Fe-EDTA is only available up to pH 6. The chemical stability of this chelate is limited. In high pH soils is not efficient. This kind of chelates is more useful for metals like Zn, Cu and Mn.
When we look more close to iron chelates and there stability, the chelate structure changes with changing pH value. At low pH levels the Fe3+ is replaced by H+ and in severe cases (pH<3) the chelate structure will be destructed. On the other hand at high pH levels Fe3+ is replaced by Mg2+ and Ca2+.
Fe3+ + 3 OH- ® Fe(OH)3 reaction also does lead to precipitation.
In the graph, Iron stability with different chelate agents at different pH levels can bee seen. As it is seen clearly the only chelate agent that is stable in all conditions is EDDHA.
There is different kind of chelate agent to use in different conditions.
Due to different stability:
- Fe-EDTA for foliar applications and acid soils
- Fe-DTPA in greenhouse substrate (rockwool, peat) and neutral soils, where pH can be up to 7.
- Fe-EDDHA in soil, pH can be up to 8,5.