Exchangeable sodium accumulation and replacement in Southeast Texas soils under turfgrass

Abstract

Many municipal water supplies in Southeast Texas have a relatively high level of Na+ and low total dissolved solids. Most soils of this area are dominated by smectitic clays that respond to wetting by swelling, especially when wetted with high Na waters of low salinity. This study assessed the degree of Na accumulation in Southeast Texas soils under irrigated turfgrass, tested models predicting Na accumulation, and evaluated response of sodic soil to amendments. The Ap, E, and Bt horizons of 18 turf soils in 10 municipal water districts were studied. Irrigation water sodicity (SARiw) and salinity (ECiw) were strongly correlated with soil sodicity (SARE) and salinity (ECe). The SAR,W was found to be the best single variable to model soil Na accumulation but exchangeable Na also increased as a function of years of irrigation. The multiple regression equation: SARE =-5.16 + 0.53 SARiw + 4.04 In (yr) (R2 = 0.86) best predicted SARE to a depth of 30 cm. This study also compared gypsum, a common amendment for sodic soil reclamation, to langbeinite. A column leaching experiment using sodic water was conducted on a sodic, non-saline Boonville soil (fine, montmorillonitic, thermic Ruptic Vertic Albaqualf) amended with gypsum and langbeinite at rates equivalent to exchangeable Na in soil depths of 15 and 30 cm. The soil water at depths of 7.5, 15 and 22.5 cm and the effluent from each column were collected at intervals of 12 h and analyzed for sodium adsorption ratio (SAR) and soluble bases. Saturated hydraulic conductivity (Ksat) was calculated. At the end of the experiment, soil samples were removed from each column in four depth increments. Significantly less exchangeable Na and lower SAR of the soil waters were found in the lower sections of the soil columns, and Ksat was greater for the amended treatments than for the control.