A model for prediction of calcium-sodium exchange reactions in sodic soils

Abstract

The material balance equation that describes the miscible displacement involving cation exchange was solved numerically for prediction of calcium-sodium exchange during reclamation of sodic soils. This exchange process was studied for Fatehpur loamy sand and Bhabiana loam. Four columns of each soil were packed and saturated with sodium by leaching with 0.1 M sodium chloride solution. The adsorbed sodium was displaced by 0.50 M calcium nitrate solution. Different volumes of calcium nitrate solution were passed to cause differential removal of exchangeable sodium. Nonlinear exchange isotherms were developed for the soils and incorporated in the convective-dispersive transport equation, which was solved by finite difference technique. Good agreement between the computed and experimental profiles of soluble and exchangeable calcium following input of different volumes of calcium nitrate solution was obtained. Last traces of exchangeable sodium which were difficult to remove from Bhabiana loam were not predicted by the model. Reasons for this discrepancy are enumerated.