ARS | Publication request: EFFECT OF SAR ON WATER INFILTRATION UNDER A SEQUENTIAL RAIN-IRRIGATION MANAGEMENT SYSTEM

Submitted to: Agricultural Water Management
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: July 19, 2006
Publication Date: September 7, 2006
Citation: Suarez, D.L., Wood, J.D., Lesch, S.M. 2006. Effect of SAR on water infiltration under a sequential rain-irrigation management system. Agricultural Water Management. 86:150-164.

Interpretive Summary: Use of degraded waters for irrigation will require increased knowledge of the short and long-term impacts on soil properties and the needed management practices for sustained use. Existing sodium criteria for irrigation are based mostly on short- term laboratory experiments with continuous water flow in packed soil columns. We examined an outdoor system with cyclic irrigation of water and simulated rainfall with drying cycles between irrigations for one year. We utilized 2 soils from the Upper Great Plains, where irrigation is applied to augment rainfall. The irrigation water treatments consisted of 2 salinity levels and 5 sodicity (SAR) levels. We observed decreased water infiltration starting above SAR 2 for the loam soil and above SAR 4 for the clay soil. These results suggest greater sensitivity to sodium than indicated by existing water quality criteria. Adequate criteria need to be site specific, considering soil types and local climatic conditions such as quantity and timing of rain events during the year. These results are applicable to water quality criteria in areas where rainfall is a significant component of the water crop water budget.

Technical Abstract: 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 packed (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 and EC=2 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 little difference EC there was little difference in the infiltration changes. 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.