[S,S]-EDDS/Fe: a new chelate for the environmentally sustainable correction of iron chlorosis in calcareous soil

Iron deficiency in crops is usually prevented and cured by the application of synthetic Fe chelates such as EDTA/Fe and the o,o-EDDHA/Fe. However their persistence in soil calls for the implementation of new alternatives that present less of a risk to the environment. This study therefore evaluated the biodegradable chelating agent [S,S]-EDDS as a new source for Fe fertilisation in calcareous soils in relation to its chemical reactivity. The suitability of [S,S]-EDDS/Fe as an Fe fertiliser in a calcareous soil was investigated and compared to the traditional synthetic chelates EDTA/Fe and o,o-EDDHA/Fe. Plant experiments with soybean (Glycine max), 57Fe isotopic labelling, and batch incubations were conducted in a calcareous soil. The Fe concentration of plants treated with [S,S]-EDDS/Fe was similar to those treated with EDTA/Fe. A similar Fe concentration to the o,o-EDDHA/Fe treatment was achieved using a double dose of [S,S]-EDDS/Fe. Despite the degradation of [S,S]-EDDS limiting the durability of [S,S]-EDDS/Fe in soil, the Fe bound to the degradation products may be a determining factor in improving Fe uptake and translocation to leaves in plants treated with [S,S]-EDDS/Fe compared to other Fe sources. Speciation studies by modelling and batch experiments also supported the lower reactivity of [S,S]-EDDS/Fe with calcium compared to that of EDTA/Fe, possibly contributing to the permanence of [S,S]-EDDS/Fe in the calcareous soil. This study demonstrated for the first time, that [S,S]-EDDS may be an environmentally sustainable alternative to traditional synthetic chelating agents such as EDTA or o,o-EDDHA for curing Fe chlorosis in susceptible plants in calcareous soil.