عنوان مقاله [English]
نویسندگان [English]چکیده [English]
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.