Kinetics of Phosphate Leaching in Undisturbed Columns of Alkaline Soil of Kota, Rajasthan

The kinetics of leaching of phosphate has been studied on undisturbed columns of alkaline soil (pH=8) of Kota region of Rajasthan. Disodium hydrogen phosphate (Na₂HPO₄) has been taken as source of added phosphate. Initial leaching rates (LR_obs) were calculated for the first time using Latshaw method and linear power form equation (LR_obs = k [PO4^3-]i^1.3) was derived for dependence of LR_obs on leachable concentration of phosphate present initially in the column during leaching. Various extractants viz. sodium bicarbonate, sodium oxalate, sodium citrate and water were used to witness leaching. Detailed kinetics was followed with 0.5 M NaHCO3 as extractant. Change in water filled porosity (θ, cm³ cm⁻³) of the column has did not affect the LR_obs. An increase in temperature in the range 25 to 50°C increased the LR_obs. Experimental data when fitted on various kinetic models showed zero and first order kinetic models to be most suited while parabolic diffusion and Elovich equations could be rejected.