The rate and activation energy relationships of potassium release from the soils of sub-humid and arid regions of Punjab

The rate and energy relationship of potassium release upon their interaction with hydronium ion (H₃O⁺) was studied. The rate of potassium release was measured from sub-humid and arid region soils and their fractions in 0.1 M HCl and 0.1 M HNO₃ acid solution at 25 and 35°C for various time intervals up to 264 hours. Activation energy of potassium release from soils and their fractions were calculated by fitting the values of rate constant at two different temperatures (25°C and 35°C) to the Arrhenius equation. Potassium release from both the soils and their respective fractions was best described by Elovich equation. The rate constant of potassium release was higher for the arid region soil than that for the sub-humid region soil. The rate constant of potassium for soil fractions in both the soils was in order of clay>silt>sand, while reverse was the order recorded for heat of activation in the fractions of both the soils. Activation energy of the sub-humid and arid soils were 11.98 and 6.09 kcal mol⁻¹, respectively in 0.1 M HNO₃ solution and 10.92 and 5.76 kcal mole⁻¹, respectively in 0.1 M HCl solution. The higher magnitude of activation energy of K release for the sub-humid soil relative to the arid soil describes the slow rate of K release in former. Release of K in aqueous solutions was controlled by the film-diffusion process. Activation energy was low in the arid region soil due to the presence of higher amounts of easily weatherable trioctahedral mica. Soil of sub-humid region was rich in dioctahedral mica, which has relatively more stability to weathering. The atomic bonding energy of potassium-bearing minerals present in soils controlled the characteristic rate of potassium release.