The relevance of bypass flow on water flow, solute or pesticide transport is becoming increasingly recognized. Recent investigations proved that soil salinization may be influenced by bypass flow, i.e. the rapid transport of water and solutes via macropores and/or shrinkage cracks to subsoil and groundwater. This paper explores the role of bypass flow in the process of accumulation and leaching of solutes, as well as of sodium, in a Mediterranean cracking soil irrigated with saline/sodic waters. The results of bypass flow experiments performed on undisturbed soil cores showed that leaching of solutes occurred in concomitance with bypass fluxes when a low salinity solution was alternated with a high salinity solution. Exchange of solutes between the incoming solution and the soil matrix occurred during the bypass flow events at the contact surfaces (cracks walls) between the solution and the soil matrix and where cracks terminated in the soil samples. Concomitant exchanges of sodium were indicated by measurements performed in the effluent solution during the bypass flow measurements. The amount of Sodium released from the soil during the bypass flow events, as well as that of the soluble salts leached from the soil, were found to depend on the degree of soil cracking. These results indicated that: 1 in management of irrigation in cracking soils, under the occurrence of bypass fluxes, alternating a low salinity/sodicity water with a high salinity/sodicity solution can be effective for preventing salinization and sodification: 2 greater efficiency of removal of sodium/soluble salts can be obtained if application of the leaching solution is performed when the soil is at a considerable degree of cracking.
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