Department of Soils, Haryana Agricultural University, Hissar, 125004, Haryana
Cation exchange equilibria involving Al—Ca, Al—K and Al—NH4 were studied in three texturally (i. e. sandy loam, clay loam and silty clay loam) and mineralogically different acid soils of the state of Assam. The normalized exchange isotherms for different soils and cat ionic systems were drawn and the results were interpreted in terms of thermodynamic selectivity coefficients and approximate free energy changes (ΔGr′) of the exchange reactions.
The normalized exchange isotherms indicated the order of preference for the competing cations Al>Ca>NH4>K, whereas the values of ΔGr′ showed the order: NH4>K>Al>Ca. The higher thermodynamic preference to NH4 and K over Al was ascribed to significant content of dioctahedral mica together with vermiculite and smectite. The soil, rich in mica (silty clay loam) showed relatively greater preference for NH4 and K over Al than the one with relatively low mica content (sandy loam).
Cation exchange, selectivity coefficient, exchange isotherm, free energy
