Deviations from the empirical sodium adsorption ratio (SAR) and exchangeable sodium percentage (ESP) relationship

Accurate information on exchangeable sodium percentage (ESP) is important in reclamation of sodium (Na)-affected soils. Representative soil samples were collected at six depths (0-5, 5-15, 15-30, 30-60, 60-90, and 90-120 cm) from five sites in the Powder River Basin (PRB), Wyoming, that have been irrigated with saline-sodic water [electrical conductivity of irrigation water (ECiw) >2 dS m and sodium adsorption ratio of irrigation water (SARiw) >20 mmol L] for up to 3 years. Soil ESPs were determined using NH4OAc (ESPm) and the ESP-SAR empirical relationship (ESPe) recommended by U.S. Soil Salinity Laboratory Staff. Measured ESPm values were significantly lower (P < 0.05) than ESPe determined by the empirical relationship in the upper 30 cm; except for site 2, all remaining profiles had no statistically significant relationships for 30- to 120-cm depth samples. Significantly lower ESPm in these soils could be due to a combination of overcorrection for soluble Na because of salinity and underestimation of exchangeable Na due to fixation of the NH4 index ion by smectitic clay minerals present in the PRB soils. Thus, using an appropriate extractant to determine the exchangeable Na and using a correction factor for accurate evaluation of soluble Na concentrations are important for developing suitable amendment plans for correcting sodicity hazard in saline-sodic waters used to irrigate soils of the PRB region. Copyright 2006 by Lippincott Williams & Wilkins, Inc.

Deviations from the empirical sodium adsorption ratio (SAR) and exchangeable sodium percentage (ESP) relationship Academic Article