Fe chelates for remediation of Fe chlorosis in strategy I plants

Iron chlorosis is a mineral disorder due to low Fe in the soil solution and the impaired plant uptake mechanism. These effects increased with high pH and bicarbonate buffer. The solution to Fe chlorosis should be made by either improving the Fe uptake mechanism or increasing the amount of Fe in the soil solution. Among Fe fertilizers, only the most stable chelates (EDDHA and analogous) are able to maintain Fe in the soil solution and transport it to the plant root. In commercial products with the same chelating agent, the efficacy depends on the purity and the presence of subproducts with complexing activity, that can be determined by appropriate analytical methods such as HPLC. In commercial products declaring 6% as Fe-EDDHA, purity varied from 0.5% to 3.5% before 1999, but in 2002 products ranging 3-5.4% chelated Fe are common in the Spanish market. Fe-o,p-EDDHA, as a synthesis by-product with unknown efficacy, is present in all Fe-EDDHA formulations. Commercial Fe-EDDHMA products also contain methyl positional isomers. Fe-EDDHSA synthesis produces condensation products with similar chelating capacity to the Fe-EDDHSA monomer that can account for more than 50% of the chelated iron in the commercial products. Chelates with different molecules should be compared for their efficacy considering firstly their ability to maintain Fe in solution and secondly their capacity to release iron to the roots. Accepting the turnover hypothesis, their efficacy is also dependent thirdly on the ability of the chelating agent to form the chelate using native iron from the soil. The 1st and 3rd points are related to the chemical stability of the chelate, while plants make better use of iron from the less stable chelates. Plant response is the ultimate evaluation method to compare commercial products with the same chelating agent or different chelates.