Cation exchange in laterite soils – A critical assessment based on Net Ionic Equilibrium (NIE)

An extensive study of exchange properties of surface and subsurface soil samples of the main campus of Kerala Agricultural University, Vellanikkara, covering a total of 914 samples was conducted. The 0.1 M BaCl₂ extractable exchangeable ions, CEC and the relative factor(s) in terms of ionic ratios of monovalent (K⁺ and Na⁺) ions to the divalent and/or trivalent ions, computed based on ratio law were subjected to regression analysis in an attempt to predict the contents of the exchangeable ions. In the case of exchangeable K and Na, the ratios [K/(Ca + Mg + Mn + Fe)^1/2 + (Al)^1/3] and [Na/(Ca + Mg + Mn + Fe)^1/2 + (Al)^1/3], respectively, could predict 60 to 70 per cent of the variation in the content of these ions in the exchange fraction, while CEC could explain only 12.4 to 14.7 per cent and percent base saturation (PBS) only 10% of the variability.