Department of Soils, Punjab Agricultural University, Ludhiana, Punjab
*Present addresses: Faculty of Agriculture, University of Guyana, George Town, Guyana, South America
**Present addresses: Department of Soil Science and Agricultural Chemistry, Rajendra Agricultural University, Pusa, Samastipur, Bihar
The kinetics of the reactions of Fe-DTPA and Fe-fulvate with soils differing in calcium carbonate content was studied. The reaction of Fe-DTPA between 2 and 48h with these soils conformed to first order kinetics. The experimental data were analysed according to a kinetic model developed for the reaction of iron chelates with soils. As predicted by the model, the kinetic constant for the loss of iron from soil solution, was equal to the sum of kinetic constants of the formation of DTPA chelates of the main competing cations. The kinetic constant for the loss of Fe from Fe-DTPA ranged between 10.5 and 26.8×10−3(h−1) in the soils under study. The subsequent reaction of Fe-DTPA beyond 48h was marked by a slow diffusion-controlled release of Zn2+ and Cu2+ from their reserve labile pools. The Fe-fulvate macromolecules were adsorbed very rapidly by the soils. The subsequent displacement of Fe from the surface bound Fe-fulvate by Ca2+, Zn2+, Cu2+ and Mn2+ may occur slowly as the reaction proceeds.
Fe-DTPA, Fe-fulvate, kinetic constant
