Comparison of the Effect of Chloride and Orthophosphate Anions on the Kinetics of Non-Exchangeable Potassium Release in Some Calcareous Soils

Arid region soils are generally considered rich in micaceous K minerals. These soils have a significant amount of interlayer K for plant uptake. Availability of nonexchangeable K (NEK) is not only dependent on the quantity of interlayer K, but also on the release rate from the mineral phase in the soil. The aim of this study was to compare the effect of H2PO4- and Cl- anions on the NEK release kinetics in 10 calcareous soils. The NEK release kinetics was studied by using 0.01 M CaCl2 and 0.01 M Ca(H2PO4)2 extractors in a periods of 1-2017 h. The results showed that the NEK release included an initial fast reaction (up to 168 h) and a slow reaction in the two extractants. The mean cumulative NEK released after 168 h in 0.01 M CaCl2 and 0.01 M Ca(H2PO4)2 was 220.3 and 137.5 mg.kg-1, respectively. The mean cumulative NEK released after 2017 h in 0.01 M CaCl2 and 0.01 M Ca(H2PO4)2 was 391.3 and 252.3 mg.kg-1, respectively. Higher NEK release rate in CaCl2 than Ca(H2PO4)2 was described by the zero order, simplified Elovich, power function and parabolic diffusion models in CaCl2 and Ca(H2PO4)2 solutions and in both segments. The results of this research showed that anions associated with cation can affect the kinetics of NEK release.