Asian Journal of Soil Science and Plant Nutrition

Thermodynamic criteria were used to evaluate the adsorption and release of potassium in saline soils. The study was conducted on three sites that differ in salt content in Nineveh Governorate - Iraq, and each site is divided into two depths (surface and subsurface). The study was conducted at three temperatures (278, 298, 318 Kelvin). The results of the study showed that there was an increase in the amount of potassium adsorbed and the percentage of adsorption with an increase in the amount of potassium added in all the studied soil samples. For the ability of the soil to the adsorption, the results showed a sudden increase in the adsorption of potassium at the application of the high levels (1 and 2 mmolL^-1) of potassium in all the studied soils. Also, the highest value of the ionic activity of potassium (AR_k) was (14.05 × 10^-3 molL^-1/2), at a temperature of 298 K in the subsurface soil layer of the first site, while the lowest one was (1.61 × 10^-3 molL^-1/2), in the same layer of the first site at a temperature of 278 K. The values ​​of free energy of potassium, ΔG_K, in the studied soils ranged from the highest value reached (-14.85×10^-3 kJ) at a temperature of 278 K, to the lowest value, reached (-10.56×10^-3 KJ) at a temperature of 298 K, in the subsurface soil layer of the first site. Regarding the values ​​of entropy reaction, they ranged from the highest value of -53.43 Jmol^-1 in the subsurface depth of the first site at a temperature of 278 K to the lowest value of -35.46 in the same layer of the first site at a temperature of 298 K. On the other hand, the enthalpy values ​​of the studied soil samples were negative, which indicates that the reaction is of the exothermic type, where the highest negative value for enthalpy was -29.70 kJmol^-1 at a temperature of 278 K in the subsurface soil layer of the first site and the lowest negative value, was -20.42 kJmol^-1 in the same layer of the first site at a temperature of 298 K.