ESP can be estimated by the following empirical formula: ESP =[100 (-0.0126 + 0.01475 x SAR) ] / [1 + (-0.0126 + 0.01475 x SAR)].

What is exchangeable sodium percentage ESP?

The exchangeable sodium percentage (ESP) measures the proportion of cation exchange sites occupied by sodium. Soils are considered sodic when the ESP is greater than 6, and highly sodic when the ESP is greater than 15 (Table 1).

How do you calculate SAR in soil?

Although most soil reports will give you a calculated value for SAR, you can calculate SAR yourself. It's simple: SAR = Na⁺/((1/2(Ca²⁺ + Mg²⁺))^1/2 ), where Na⁺, Ca²⁺ and Mg²⁺ are all measured in meq/L (milliequivalents per liter).