Effects of Fe-EDDHA Chelate Application on Evolution of Soil Extractable Iron, Copper, Manganese, and Zinc

Abstract

Up to date, soil application of synthetic chelates is the most effective mean of controlling iron (Fe) deficiency chlorosis in many crops. The responses of three representative soils (I, II, and III) of a large orchard area (Ribera Alta del Jucar) to the application of three commercial Fe-EDDHA chelates (Sequestrene 138 Fe G-100, Group Carla Val F.E.A 6 Superior and Ferrishell plus) at 100 (D1) and 200 μg Fe/kg of soil (D2) were analyzed. Extractable concentrations of Fe, copper (Cu), manganese (Mn), and zinc (Zn) were determined at 7, 14, 21, 42, and 71 days after the application. Data were subjected to multifactor ANOVA to analyze the effects of time, dose, soil, and chelate type on Fe, Cu, Mn, and Zn concentrations. Soil type affected the recovery percentage of Fe by DTPA extraction. The extractable Fe increased to 40-60 mg Fe/kg of soil by the D1 dose and to 70-100 mg Fe/kg of soil by the D2 dose for soils I and II. However, in the case of soil III, recovery increased to 60-80 mg Fe/kg of soil for D1 and 100-140 mg Fe/kg of soil for D2. As the pH of the three soils was similar, this recovery difference is attributed to the differing textural compositions of the soils. The extractable concentrations of Fe increased in the sandy loam soil in contrast to the clay loam soils. The Fe-EDDHA formula did not affect significantly extractable Fe concentration. Increases in the extractable Cu and Mn were observed after Fe-EDDHA soil application. These increases could be due to changes in the redox potential that alters the form and solubility of some metals, possibly affecting the metal-chelate equilibrium. In the case of Zn, the variation in Zn concentration is hardly appreciable, with Fe preventing effective Zn chelation. No difference in effectiveness has been found between the Fe-EDDHA formula brands used in this experiment.