SAR-ESP Relationships

Some differences in the SAR-ESP relationship between the two humid soils (Figs. 11.1 -11.4) are also apparent. The data indicate that the SAR-ESP relationship of the Pembroke soil is independent of chloride (Cl-) and to some degree pH, but this is not true for the Uniontown soil. It appears that as pH increases, the Uniontown soil shows a strong adsorption preference for Na+, but as Cl concentration increases, it shows a 

In summary, if one discharges brine onto a soil with a strong Na+ adsorption potential, this soil will protect the groundwater fromNa+ contamination at the expense of its own potential Na+ contamination. However, a soil with low Na+ adsorption potential will protect itself from Na+ contamination at the expense of potential groundwater contamination. 

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The sodium adsorption potentials of two humid soils are presented in some detail and the SAR-ESP data are shown in Figures 11.1-11.4. For comparison purposes, these figures also include the SAR-ESP relationship of salt-affected soils found in arid-region soils (western United States). Figures 11.1-11.4 show that for any given SAR, the ESP for either one of the two humid soils is greater than the ESP of the western U.S. soils. This indicates that the two humid soils adsorb sodium on their exchange complex more effectively than the western U.S. soils. 

The U.S. Soil Salinity Laboratory Staff (1954) reported that SAR values of 10-15 (mmol L )1/2 usually correspond to ESP values in the range of 10-15 at which values clays will undergo dispersion. This relationship may vary among colloids with different mineralogy (Oster et al., 1980) and/or mixtures of colloids with different mineralogy (Arora and Coleman, 1979). Consequently, the force by which given types of colloidal particles attract or repulse each other in a Na-Ca or Na-Mg solution is a function of the total concentration of the salt, the type of divalent cation (Ca or Mg), and SAR. Therefore, pH, salt concentration, type of divalent cation, and SAR are expected to play important roles on soil colloid flocculation. 

Exchangeable sodium percentage is related to the relative ratio of Na to Ca1/2 in the solution phase, which is referred to as the SAR (see Chapter 4). An empirical relationship between SAR and ESP, representing soils of the arid west, was developed by the U.S. Salinity Laboratory Staff (1954) ... 

Figure 11.1. Relationship between percentage of CEC loaded with sodium (ESP) and SAR at three chloride concentrations of Pembroke soil at pH 4.3 (the solid line without data represents most salt-affected soils in the western United States it was produced using Eq. 11.4) (from Marsi and Evangelou, 1991a, with permission).

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