Th e sodium adsorption ratio (SAR) and salinity criteria for water suitability for irrigation have been developed for conditions where irrigation water is the only water source. It is not clear that these criteria are applicable to environments where there is a combination of rain and irrigation during the growing season. Th e interaction of rainfall with irrigation water is expected to result in increased sodicity hazard because of the low electrical conductivity of rain. In this study we examined the eff ects of irrigation waters of SAR 2, 4, 6, 8, and 10 mmol 1/2 L −1/2 and electrical conductivities of 1 and 2 dS m −1 on the infi ltration rate of two soils with alternating cycles of rain (simulated with a rainfall sprinkler) and irrigation water, separated by drying cycles. Th e infi ltration rate of surface samples from two soils, Kobase silty clay (fi ne, smectitic, frigid, Torrertic Haplustept) and Glendive very fi ne sandy loam (coarse-loamy, mixed superactive, calcareous, frigid Aridic Ustifl uvent) were evaluated under alfalfa (Medicago sativa) cropped conditions for over 140 d and under full canopy cover. Reductions in infi ltration were observed for both soils for SAR above 2, and the reductions became more severe with increasing SAR. Saturated hydraulic conductivity measurements taken from undisturbed cores at the end of the experiment were highly variable, suggesting that in situ infi ltration measurements may be preferred when evaluating SAR eff ects. ) is a good estimator of the exchangeable sodium percentage (ESP) (U.S. Salinity Laboratory Staff , 1954) and has been used to develop numerous water quality criteria for irrigation (Ayers and Westcot, 1985). For a given SAR value, the adverse impacts on soil physical properties are reduced with increasing salinity (Ayers and Westcot, 1985), commonly reported as the EC in dS m −1 (electrical conductivity of the solution).
Infi ltration intoTh ere are many studies documenting the adverse eff ects of sodicity on soil hydraulic properties, mostly saturated hydraulic conductivity (K s ) in packed columns run for short periods of time under continuous water fl ow. McNeal and others (McNeal and Coleman, 1966;McNeal et al., , 1969McNeal, 1968) characterized the eff ects of EC and SAR on soil K s and soil swelling. Th ey observed a range in soil stability for arid land soils of the southwestern USA. Th ey concluded that soils high in kaolinite and sesquioxides seemed to be more stable and soils high in smectite the least stable . Frenkel et al. (1978) examined the saturated K s of several soils of varying mineralogy as related to their response to diff erent EC-SAR levels. Th e soil with kaolinitic clay was the most stable, followed by the soil with vermiculitic clay, and the smectitic clay soils were the most sensitive to SAR. However, these experiments lack data below SAR 10 and provide no information in the salinity range between EC = 1 dS m −1 and deionized water. Th ere are only a few studies where dilute waters were applied and infi ltration or K s mea...
