A test to evaluate the efficacy of commercial Fe‐chelates

Abstract

A large number of Fe fertilizers are used to correct iron chlorosis, most of them based on Fe‐EDDHA or Fe‐EDDHMA chelates. Our objective was to establish a laboratory test to evaluate in a rapid and simple way the capacity of a Fe‐chelate to maintain Fe in solution. The proposed test consisted of a two‐step procedure. First, the Fe‐chelate in solution was shaken with NaOH (pH=11.5) and after filtration (0.45 μm pore) pH is restored to 7.5. Next, the solution was treated with an excess (=600x) of the chelating agent DTPA. Red chelates, which present absorbances at 480 nm, were used in the test. Experimental conditions were initially studied using the speciation model Geochem and experimentally established. Fe concentration measured by atomic absorption and visible spectroscopy after the test application allowed us to obtain several indexes which indicated the chelate stability and were related to the concentration of Fe in the solution where plant roots grew. The test is useful in determining the relative efficiency of new products with respect to other, better known brands.