Effect of SAR on water infiltration under a sequential rain–irrigation management system

Existing irrigation water quality criteria related to sodium and salinity are based primarily on short-term laboratory column studies. These earlier studies measured infiltration or hydraulic conductivity of disturbed soil under continuously saturated conditions. Application of these standards to field conditions is uncertain, as it does not account for wetting and drying conditions, formation of crusts and impact of rain events, etc. In this study we examine water infiltration into loam and clay soils irrigated at EC = 1.0 and 2.0 dS m −1 at SAR of 2, 4, 6, 8, and 10 in a management system with alternating (simulated) rain and irrigation and drying between irrigations. For the loam soil the adverse impacts of sodium on infiltration were evident above SAR 2, while for the clay soil adverse impacts occurred above SAR 4. In both soils the SAR behavior was similar for both EC values, 1.0 and 2.0 dS m −1 , indicating that in this range, EC did not affect infiltration. Reductions in infiltration were evident during both the irrigation and rain events, with lower infiltration, as expected during the rain simulations. These results show a greater sensitivity to SAR than indicated in laboratory column studies and existing water quality criteria.