Kinetics of DTPA extraction of zinc from calcareous soils from Iran

摘要

In recent years, our knowledge of Zn extraction from soil has been based mainly on the study of equilibrium condition using thermodynamic approaches. Thermodynamics can predict only the final state, while a knowledge of desorption kinetics may yield important information concerning the nature of reactions and also the rate of supply of Zn to plants via soil solution. The kinetics of Zn extraction by diethylenetriaminepentaacetic acid (DTPA) from the -2mm fraction of 12 calcareous soils was investigated using surface soil (0-30 cm) samples. Soils were equilibrated with 0.005 M, DTPA solution for 15 to 11520 minutes. Zero-, first-, second-, third order, parabolic diffusion and simple Elovich equations did not adequately describe Zn extraction kinetics. The best model for describing extraction data for all soils was the exponential rate equation (q=a tb). The magnitude constant, a, was significantly and positively correlated (r = 0.76) to organic carbon content and negatively correlated to pH (r = -0.67). The rate constant, b, was not significantly related to any of the measured soil properties (pH, CEC, CCE, ACCE, clay, OC, S SA) or to any combination of properties. It was concluded that the amount of Zn that can be extracted by DTPA solution from Iranian calcareous soils is highly variable.