Soil salinization as a threat to the sustainability of deficit irrigation under present and expected climate change scenarios

Deficit irrigation (DI) strategies using moderately saline waters save water, but may enhance soil salinization. Based on data gathered during years 2007-2012 in three drip-irrigated grapevine, peach, and nectarine crops subjected to several irrigation and soil-mulching treatments, we assessed trends in root-zone soil salinity [saturation extract electrical conductivity (ECe)], related the changes in soil salinity (Delta ECe) to field-wide leaching fraction (LF), evaluated management strategies for soil salinity control, and examined the sustainability of DI strategies under present and expected climate change (CC) scenarios in the Middle Ebro River Basin (ERB, Spain). ECe increased in 82 % of the irrigation seasons and decreased in 75 % of the non-irrigation seasons examined. Soil salinization trends were not apparent during the study years due to these annual salt accumulation-salt leaching cycles. ECe increases were higher in the more severe DI treatments and in the geotextile-mulched soil and lower in the full and less severe irrigation treatments and in the organic-mulched soil. As expected, Delta ECe and LF were linearly and negatively correlated (P < 0.01), indicating that soil salinization increased with decreasing LF. These linear relationships provided a way to evaluate best management strategies (increased irrigation, rainfall harvesting, and soil mulching) for soil salinity control. These strategies decreased soil salinization, but did not guarantee the sustainability of severe DIs in the study area. The application of these relationships to the CC precipitation and crop evapotranspiration projections in the ERB shows that the examined DI strategies will be unsustainable due to soil salinization.