Kinetics of Zinc Desorption and Relations of Kinetics Parameters with Properties of Some Soils of Iran

The rate of Zn desorption from soil surfaces into soil solution is a dynamic factor that regulates it continuous supply to growing plants. To ascertain the pattern of Zn desorption and the effective soil characteristics, the kinetics of Zn desorption from 20 selected soils of Iran by diethylentriaminepentaacetic acid (DTPA) were investigated. Eight kinetic models were evaluated to describe the rate of desorption of soil Zn by DTPA, which was rapid initially but gradually declined with time. The simple Elovich, the parabolic double diffusion and the two constant rate equations adequately described Zn desorption from soils. Rate constants for the parabolic double diffusion equation (K1 and K2), the two constants (a and ab), and parabolic diffusion (Kd) were closely correlated with soil pH, calcium carbonate equivalent, Olsen-P and DTPA-Mn, which are the soil characteristics that affect solubility, desorption and diffusion of Zn in soils. Rate constant for the simple Elovich equation (βs) was correlated with Olsen-P and rate constant for two-constant equation (b) was correlated with CEC, organic carbon and FC. The ratio of initial Zn desorption (rapid desorption) to total Zn desorption of soils decreased significantly with increase in calcium carbonate equivalent of soils.