Exchangeable Sodium Percentage (ESP)

“Exchangeable Sodium Percentage (ESP)” is the relative amount of the sodium ion present on the soil surface, expressed as a percentage of the total Cation Exchange Capacity (CEC). Since the determination of CEC is time consuming and expensive, a practical and satisfactory correlation between the Sodium Adsorption Ratio (SAR) and ESP was established. The SAR is defined elsewhere in this Section. ESP can be estimated by the following empirical formula:
ESP =[100 (-0.0126 + 0.01475 x SAR) ] / [1 + (-0.0126 + 0.01475 x SAR)].

Source: Corporation Commission, Oil and Gas Conservation, Oklahoma Administrative Code 165:10, February 2013. Regulations

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