The biodegradability of EDDHA chelates under calcareous soil conditions

FeEDDHA (iron (3+) ethylenediamine-N,N′-bis(hydroxy phenyl acetic acid) products are commonly applied to mend or prevent Fe chlorosis in plants. In soil application, racemic and meso o,o-FeEDDHA are the effective components, while o,p-FeEDDHA tends to adsorb or react to o,p-CuEDDHA. Upon interaction with soil, a plant-independent, gradual decline in soil solution concentration of meso o,o-FeEDDHA and o,p-CuEDDHA has been observed. The aim of this study was to examine to what extent biodegradation contributes to this gradual decline. A 4-week incubation experiment was done with calcareous soil to which FeEDDHA was added. The experiment involved three sterility regimes, two conditioning regimes and three time steps. Soil solution concentrations of meso o,o-FeEDDHA and o,p-CuEDDHA gradually declined in all sterility regimes. Biodegradation did not significantly contribute to the decline in concentration of any EDDHA chelate, except for CoEDDHA, which was formed in small quantities as a result of cation displacement. The rate of the process causing the decline in meso o,o-FeEDDHA and o,p-CuEDDHA concentration was higher at higher temperature and in soil not exposed to gamma irradiation. This study offers no evidence that the effectiveness of soil-applied FeEDDHA fertilizers is compromised by biodegradation. ► Biodegradation does not compromise the performance of FeEDDHA in soil application. ► Higher temperature increased the rate of decline in EDDHA chelate concentrations. ► Gamma irradiation decreased the rate of decline in EDDHA chelate concentrations. ► Including reinoculated treatments proved essential for correct interpretation.