Replacement of Adsorbed Sodium in Soils by Hydrolysis of Calcium Carbonate

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Abstract
The reaction 2Naadsorbed + CaCO3 + H2O ⇆ Caadsorbed + 2Na+ + HCO3‐ + OH‐ has been studied from the standpoint of describing the replacement of adsorbed Na in calcareous soils subjected to leaching by rainfall. It has been found for the reaction in soils that the equilibrium between solution and adsorbed Na at various water contents can be expressed by the Langmuir equation: Naad = (k1k2Na+)/(1 + k1Na+) where k1 and k2 are constants, and Naad and Na+ are the adsorbed and solution concentrations of Na, respectively. As a consequence of this finding, it has been shown that the concentrations of solution and adsorbed Na at any depth in soil columns after a known amount of leaching with salt‐free water can be satisfactorily predicted by simplified, approximate solutions of equations derived by Thomas, Hiester, and Vermeulen. The results should be especially useful where calcareous soils, which have been affected by sea water, are subsequently leached by rain‐fall.

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