Saturated Hydraulic Conductivity of Semiarid Soils: Combined Effects of Salinity, Sodicity, and Rate of Wetting

als, high pH, and low sesquioxides content was found to be susceptible to sodic conditions, with the magnitude Combined effects of soil conditions (wetting rate), soil sodicity, of the decrease in HC being strongly dependent on the and salinity on soil saturated hydraulic conductivity (HC) have not been studied systematically and were the objective of our study. We electrolyte concentration in the soil solution (Shainberg examined the effects of (i) exchangeable sodium percentage (ESP, and Letey, 1984). 1–20) and fast wetting (50 mm h 1) and leaching with distilled water Unlike inherent soil properties, the effects of tempoon the HC of 60 Israeli soils (7–70% clay); and (ii) wetting rate (2 ral changes in the conditions prevailing in the soil (e.g., or 50 mm h 1), ESP and water salinity (distilled water or saline water, rate of wetting, antecedent moisture content and aging 2 dS m 1) on the HC of 16 selected samples. Results of the first duration) on the response of soils to sodic conditions experiment showed that (i) steady state HC of mediumand finehave received less attention (Shaw et al., 1998). As a textured soils was lower than 2 cm h 1 already for nonsodic soils, and result, the experimental setup under which many of the (ii) the adverse impact of sodicity on the HC strongly depended on investigations of the response of the HC to sodicity has soil texture. The second experiment revealed that in the loamy sand been studied represented extreme conditions which do rate of wetting had no effect on the HC beyond that of sodicity and salinity. In the loam, sandy clay and clay soils a significant triple not necessarily occur in the field. For instance, disturbed interaction among water quality, wetting rate and ESP in their effect soil samples were subjected to fast wetting and thereafon HC existed. In the absence of electrolytes, the impact of fast ter to an immediate measurement of soil HC. Fast wetwetting (slaking) and swelling on the HC was most notable, mainly ting of aggregates results in their slaking (Panabokke at the intermediate sodicity levels (ESP 5–10). Use of saline water and Quirk, 1957) and in a subsequent shift in the pore significantly reduced the impact of fast wetting and swelling on the size distribution toward smaller pores (Kay and Angers, HC. Our results suggested that combined effects of salinity, wetting 2000). Aggregate slaking and the subsequent change in rate, and sodicity on the HC were complex and should thus be considpore size distribution may reduce the HC, infiltration ered simultaneously when estimating soil HC. rate, and lead to runoff and erosion (Lebron et al., 2002; Levy and Mamedov, 2002). The lack of an aging period between the wetting and S hydraulic conductivity depends on the compothe measurement of the HC prevented the opportunity sition of the exchangeable cations and the composifor aggregates to regain their stability via formation of tion and concentration of the electrolytes in the soil new intraand interparticle cohesive bonds (Shainberg solution (Quirk and Schofield, 1955), as well as on soil et al., 1996). Hence, under these conditions the soils texture (Shainberg et al., 2001). The HC decreases with were noted to be very susceptible to the effects of sodian increase in the ESP (McIntyre, 1979) and the decity, salinity, and soil inherent properties (McIntyre, crease in the total electrolyte concentration of the soil 1979; Shainberg and Letey, 1984; Levy et al., 1998). solution. The reduction in the HC has been attributed However, in a natural environment, the soils are often mainly to swelling and dispersion of the soil clays (Quirk exposed to slow wetting that prevents aggregate slaking and Schofield, 1955). and could also at times stay moist for a while before The adverse effects of soil sodicity and scarcity of being exposed to rain or an irrigation event. Thus, there electrolytes on soil hydraulic properties have been studis a need to evaluate susceptibility of soil HC to sodicity ied extensively (see recent reviews by Rengasamy, 1998; under conditions that better reflect the situation of the Sumner and Naidu, 1998; Levy, 2000, and references soil in the field. cited therein). These studies have demonstrated the sigA number of studies have recently demonstrated the nificant role of soil inherent properties (e.g., soil texture, importance of rate of wetting and duration of aging on clay mineralogy, pH, and sesquioxide and lime content) the saturated HC of soils. Moutier et al. (1998) evaluated in determining the response of soils to sodic conditions. the effects of aging on the HC of a clay soil at two levels The HC of soils with high proportion of 2:1 clay minerof sodicity, 0 and 10%. Different aging durations were applied through different leaching times. It was noted G.J. Levy and D. Goldstein, Institute of Soil, Water and Environmenfor both sodicity levels that prolonged leaching (20 h) tal Sciences, Agricultural Research Organization (ARO), The Volcani of the soil maintained significantly higher HC compared Center, P.O. Box 6, Bet-Dagan 50-250, Israel; A.I. Mamedov, USDAARS-MWA, National Soil Erosion Research Laboratory, West Lafawith leaching for a short period of 3 h (Moutier et yette, IN 47907. Contributions from the Agricultural Research Organial., 1998). In an additional study, Moutier et al. (2000) zation, The Volcani Center, Bet-Dagan, Israel. No. 609/2004 series. studied the effects of rate of wetting on the HC of two Received 7 July 2004. Soil & Water Management & Conservation. calcium saturated clay soils. The results indicated that *Corresponding author ([email protected]). Abbreviations: ESP, exchangeable sodium percentage; HC, hydraulic Published in Soil Sci. Soc. Am. J. 69:653–662 (2005). doi:10.2136/sssaj2004.0232 conductivity; HCo, initial hydraulic conductivity; HCss, hydraulic conductivity at steady state; RHC, relative hydraulic conductivity at © Soil Science Society of America 677 S. Segoe Rd., Madison, WI 53711 USA steady state. 653 Published online April 11, 2005