Hysteresis Indices of Potassium Sorption-Desorption Isotherms in Some Soils of East Azarbaijan Province, Iran

Potassium (K) fixation in soils creates hysteresis phenomenon between sorption and desorption branches of the isotherm. Therefore, the hysteresis index having highest correlation with K fixation might be introduced as the most proper index for this phenomenon. For this purpose, 12 soil samples with different clay mineralogy were selected from around Dasht-e-Tabriz and Marand regions. At first, K fixation of the soils was measured by addition of 250 and 2500 mg K/kg soil. Then, K sorption isotherms at 10 initial concentrations (5-250 mg K/L) and K desorption isotherms from the point corresponding to an initial concentration of 250 mg K/L were obtained using background solution (0.01 M CaCl2) in 10 desorption cycles. The results showed that the amount of K fixation sharply decreased with increasing the saturation extract K concentration as well as the exchangeable K content. Moreover, the data obtained from both sorption and desorption branches were best fitted to the Freundlich equation. All hysteresis indices showed significant correlations with percentage of K fixed per one percent of clay. Aside from soils with high hysteresis indices, significant correlations were found between values of hysteresis indices and percentages of K fixed. The highest correlation was observed for the hysteresis index based on β exponent of the Freundlich equation.