Behaviour of iron chelates in calcareous soils

Summary An examination was made of the changes with time in the composition of aqueous extracts of a highly calcareous clay that had been treated with one of the four chelates Fe-DTPA, Fe-CDTA, Fe-HEEDDA and Fe-EDHPA (Fe-Chel 138).It was found that a rapid fall in the recovery of soluble iron took place with both Fe-DTPA and Fe-HEEDDA due to sorption by the clay and also to replacement of iron in the chelate by calcium from the soil. By using Fe⁵⁹-labelled compounds, it was found that for both these chelates considerable isotopic exchange occurred between the Fe⁵⁹ and the natural soil iron, and that this exchange increased with decreasing rate of application of chelated iron.Fe-CDTA and Fe EDHPA were found to be comparatively unaffected by contact with the soil; over 80% recovery was obtained after 15 days, with treatments ranging from 2.5 to 100 ppm chelated iron. Negligible isotopic exchange took place with these two chelates.These results are discussed in relation to previously published results of laboratory experiments with iron chelates and to the treatment of soils for the control of iron chlorosis.