Kinetics of Non-exchangeable Potassium Release from Some Soils and their Separates of Lesser Himalayas of India

The dynamics of non-exchangeable potassium (NEK) in 10 soils and their separates from different altitude zones of Kashmir valley was studied by successive extraction with 0.01M oxalic acid over a period of 200 h. The amount of NEK released after 200 h in whole soil, clay, silt and sand fractions ranged from 95.2 to 106.9, 152.1 to 161.9, 28.9 to 32.0 and 48.4 to 52.7 mg kg⁻¹, in the soils of high altitude zone, 92.8 to 95.9, 147.0 to 158.0, 28.1 to 30.8 and 47.2 to 52.7 mg kg⁻¹, respectively, in the soils of mid-altitude zone and 67.1 to 74.9, 79.2 to 103.4, 26.9 to 28.9 and 46.0 to 51.1 mg kg⁻¹, respectively, in the soils of low-altitude zone. Based on high coefficient of determination (R²) and higher values of standard error of estimate (SE), the first order, zero order and power function equations could not describe the NEK release kinetics. In contrast, Elovich and parabolic diffusion law described the data satisfactorily, indicating diffusion-controlled exchange. Rate constant variations in whole soil were attributed to differences in particle size distribution and in clay fraction, and to the type and extent of clay minerals. The data indicated that the equilibrium had not reached even after 200 h of extraction with 0.01M oxalic acid.