Calcareous soil interactions of the iron(III) chelates of DPH and Azotochelin and its application on amending iron chlorosis in soybean (Glycine max).

In order to find new greener solutions for iron (Fe) induced chlorosis, two new chelating agents, N,N-dihydroxy-N,N'-diisopropylhexanediamide (DPH) and Azotochelin (AZO), were assessed for its effectiveness in mending induced chlorosis in soybean (Glycine max). DPH-Fe and AZO-Fe complexes were firstly tested for their soil interactions and capability to maintain Fe in a bioavailable form. Secondly, 57Fe-chelates of DPH and AZO were applied to the soil in a pot experiment with chlorotic soybean plants. Their growth, SPAD chlorophyll index, and the Fe concentration in plant tissues and the remaining soil were evaluated. An isotope deconvolution analysis by using the concentration of the Fe isotopes was used to distinguish the Fe coming from soil and from the 57Fe labelled fertilizer treatments. AZO and DPH have shown different interactions with soil and its components, with AZO showing less interaction than DPH. The application of AZO and DPH resulted in SPAD increase and Fe content. However, it was found that the Fe in plants had not come from the fertilizer application, but instead from natural sources. This is likely due to dissolution phenomena aided by the chelates added. Overall, AZO and DPH have shown good results in amending Fe induced chlorosis in calcareous soils and for this reason should be regarded as good green-candidates for Fe plant nutrition in calcareous soils.