Coefficients for Estimating SAR from Soil pH and EC Data and Calculating pH from SAR and EC Values in Salinity Models

Abstract Data from highly weathered, low pH, sodic Australian soils have been used to develop a method for estimating soil exchangeable sodium percentage (ESP) or soil extract sodium adsorption ratio (SAR) from soil pH and electrical conductivity (EC) data. The method can also be used to calculate soil pH in soil salinity models using SAR and EC values. The pH was calculated as pH- A + (B x SAR112)/(1 + C x EC). Rewriting the equations in terms of SAR (or ESP), gives SAR (or ESP)-[(pH- A)(1 + C x EC)/B]2. This study was conducted to determine whether these same methods could be used to predict the pH and SAR values for arid climate soils that are only slightly weathered and are often sodic under natural conditions. Existing pH, EC, and SAR data from Declo loam (coarse-loamy, mixed, mesic, Xerollic Cal-ciorthids), Freedom silt loam (fine-silty, mixed, mesic, Xerollic Calciorthids), and Ma-zuma sandy loam (coarse-loamy, mixed (calcareous), mesic Typic Torriorthents) were used to calculate the A, B, and C coefficients for the three high sodium soils. Coeffi-cients obtained for a particular soil site were then used to predict pH or SAR of soil samples at additional sites and the correlation between calculated and measured value