KINETICS OF RELEASE OF POTASSIUM BY SODIUM TETRAPHENYL BORON FROM SOME TOP-SOIL SAMPLES OF RED (ALFISOLS), BLACK (VERTISOLS) AND ALLUVIAL (INCEPTISOLS AND ENTISOLS) SOILS OF INDIA

Alluvial (Inceptisols and Entisols) soils containing illite as dominant clay mineral released significantly higher amounts of K to 0.3 M NaTPB than smectitic Black (Vertisols) and kaolinitic Red (Alfisols) soils. Exchange rate indices derived from the plots of K released to 0.3 M NaTPB versus log t were also higher for illitic soils than for kaolinitic and smectitic soils. Magnitudes of both surface and internal K released from different soils were in the sequence: illitic > smectitic > kaolinitic. Data of K release to 0.3 M NaTPB could be described by first order rate equation. In parabolic plots, existence of a linear relationship throughout the period of exchange with NaTPB indicated the absence of film diffusion controlled processes. Diffusion coefficients calculated from radial diffusion equation were dependent upon texture and clay mineralogy of soils and decreased sharply with time for kaolinitic and smectitic soils. Illitic soils, however, maintained higher values of diffusion coefficients over extended periods of time.