The Effects of Calcium and Ammonium Cations on the Kinetics of Non-exchangeable Potassium Release in Some Calcareous Soils

The release rate of non-exchangeable potassium (NEK) plays a significant role in supplying K for plants; particularly in soils containing bearing minerals such as micas and feldespars. No study has been conducted on NEK release kinetics influence of cations in calcareous soils of Chaharmahal and Bakhtiari province. Therefore, the purpose of this study was to investigate the impact of cations calcium and ammonium (from two sources of calcium chloride and ammonium chloride) on kinetics of NEK release in 10 calcareous soils. Soil samples of calcium-saturated were extracted using successive extractions with 0.01 M CaCl2 and NH4Cl solutions for 2-2017 h at 25±1 0C. The results showed that amount of NEK released have a discontinuity in slope at 168 h. Therefore, corves were divided into two segments, including the first stage (2-168 h) and the second stage (168-2017 h). The results showed that released NEK in the studied soils in the first stage, in the 0.01 M Cacl2 and NH4cl extractors were different in the range of 96.50-220.33 and 189.67-549.50, respectively, and in the second stage, in the range of 172.67-391.33, and 320.67-748.0 mg kg-1 respectively. Based on the coefficients of determination (R2) and standard error (SE), the released NEK described in both segment and in both extractors using the zero order, power function, simplified ellovich, and parabolic diffusion equations. Also, the power function equation in both extractants was able to satisfactorily describe the kinetics of NEK release. The kinetics coefficients of the release of NEK were different in the studied soils. the use of multivariate regression equations in both segments and in both extractors of potassium release showed that the NEK release in soils depended NEK concentration, exchangeable potassium concentration and cation exchange capacity of the soil.