Exchangeable sodium percentage (ESP) is used in the classification of saline and alkali soils or to determine if a sodium hazard exists. This method requires the determination of CEC and percent exchangeable sodium (ESP). If soluble sodium is present, the exchangeable value is corrected by analysis of Na in a saturated extract.1 SAR, or sodium adsorption ratio is used to estimate or predict ESP by analyzing for Na, Ca, and Mg in a water saturated soil extract.2SAR is commonly determined on irrigation water to classify the sodium hazard.
(See Method Reference No. 17)