ABSTRACTWe carried out a laboratory study to evaluate the effect of CaCO3 and humic matter on the cation exchange equilibria of soils, involving the Ca-Na cation pair. Increasing Na/Ca ratio of equilibrium solutions increased the pH/alkalinity and cation exchange capacity of soils. The effects of increased pH and associated CEC did not change the nature of isotherms, but affected their course. Isotherms for exchange of Ca onto Na soils showed that Ca was the preferred cation, but the free energies of exchange (ΔG°Ca-Na) were found to be positive. Whereas the presence of CaCO3 increased the sodification rate, organic matter counteracted the process of sodium accumulation onto the soils. Results on the exchange isotherm and the effect of CaCO3 and organic matter on sodification and alkalinity are discussed for the natural environment of alkali soils.
We carried out a laboratory study to evaluate the effect of CaCO3 and humic matter on the cation exchange equilibria of soils, involving the Ca-Na cation pair. Increasing Na/Ca ratio of equilibrium solutions increased the pH/alkalinity and cation exchange capacity of soils. The effects of increased pH and associated CEC did not change the nature of isotherms, but affected their course. Isotherms for exchange of Ca onto Na soils showed that Ca was the preferred cation, but the free energies of exchange (ΔG°Ca-Na) were found to be positive. Whereas the presence of CaCO3 increased the sodification rate, organic matter counteracted the process of sodium accumulation onto the soils. Results on the exchange isotherm and the effect of CaCO3 and organic matter on sodification and alkalinity are discussed for the natural environment of alkali soils.
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