In-depth Insights into Zinc Desorption Kinetics from Inceptisols Using Mathematical Models

Four mathematical models viz. simple Elovich, two-constant rate, parabolic diffusion and parabolic double diffusion adequately described zinc desorption kinetics by DTPA from 10 selected Inceptisols from two watersheds of Gaya district, Bihar, for extraction periods from 0.083 h to 48 h and were evaluated for determination of rate constants of the respective models. The mean values of initial Zn desorption rate constant ‘a’ (two-constant rate), ‘α_s’ (simple Elovich), diffusion rate constant ‘k_p’ (parabolic diffusion), first diffusion rate constant ‘k^/_p’ and second diffusion rate constant ‘k^//_p’ (parabolic double diffusion) were 10.82×10^-2 (mg kg^-1s^-1)^b, 96.46×10^-4 (mg Zn kg^-1 s^-1), 1.17×10^-3 (mg kg^-1)^-0.5, 2.67×10^-3 (mg kg^-1)^-0.5 and 0.73×10^-3 (mg kg^-1)^-0.5, respectively. The mean values of desorption rate coefficient ‘b’ (two-constant rate) and zinc desorption constant ‘βs’ (simple Elovich) were 0.19 (mg Zn kg^-1 s^-1) and 15.92 (mg Zn kg^-1 s^-1), respectively. The desorption rate for all the soils included an initial short-term fast reaction followed by a long-term slower continuing reaction. Soil sample S8, having highest values of rate constants ‘ab’ (two-constant rate); ‘k_p’, ‘k^/_p’, ‘k^//_p’ and higher value of rate constant ‘αs’ (associated with lowest value of zinc desorption constant ‘β_s’) indicated highest rate of Zn desorption, among the studied soils. Correlation coefficients between rate constants and soil properties revealed oxalate extractable Fe (Fe_o), representing poorly crystalline or amorphous iron oxides, to be the most important soil factor controlling Zn desorption from the Inceptisols under investigation. The data generated from this study might be crucial for informed decisions towards optimizing nutrient management and reduced environmental impact.