Effects of Bicarbonate on Sodium Hazard of Irrigation Water: Alternative Formulation1
- S. Miyamoto2
The conventional equation using the saturation index does not satisfactorily account for the effect of bicarbonate on sodicity. We, therefore, examined the existing method and presented an alternative formulation. The alternative formulation was based on direct numerical solutions of well-known carbonate equilibrium reactions, and consisted of the solution of the second- or the third-order polynomial approximation. The analytical results were then compared with published laboratory, lysimeter, and field data. The comparison indicates that the conventional equation using the saturation index overestimates the sodicity of irrigation water having a high ratio of Ca to HCO3 and underestimates otherwise. The method also generally overestimates the sodicity of drainage water. The proposed third-power polynomial approximation yields a satisfactory prediction of the sodicity of irrigation water, of drainage water, and of surface soils. The second-order approximation can also be used for predicting the sodicity of drainage water if the pH of the drainage water is known. The proposed methods are somewhat more complex than the conventional method, but can be conveniently utilized with a programmable calculator or a mini-computer.Please view the pdf by using the Full Text (PDF) link under 'View' to the left.
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