Optimization of Irrigation of Wine Grapes with Brackish Water for Managing Soil Salinization

Water scarcity and quality are critical impediments to sustainable crop production. In this study, HYDRUS-2D was calibrated using field measurements of water contents and salinities in the soil under wine grapes irrigated with river water (<i>Rw</i>, 0.32 dS/m). The calibrated model was then used to evaluate the impact of (a) four different water qualities ranging from 0.32 (<i>Rw</i>) to 3.2 dS/m (brackish water, <i>Gw</i>) including blended (<i>Mix</i>) and monthly alternating (<i>Alt</i>) irrigation modes; (b) two rainfall conditions (normal and 20% below normal); and (c) two leaching options (with and without 30 mm spring leaching irrigation) during the 2017–2022 growing seasons. Irrigation water quality greatly impacted root water uptake (<i>RWU</i>) by wine grapes and other water balance components. Irrigation with brackish water reduced average <i>RWU</i> by 18.7% compared to river water. Irrigation with blended water or from alternating water sources reduced <i>RWU</i> by 8.8 and 7%, respectively. Relatively small (2.8–8.2%) average annual drainage (<i>Dr</i>) in different scenarios produced a very low (0.05–0.16) leaching fraction. Modeling scenarios showed a tremendous impact of water quality on the salts build-up in the soil. The average electrical conductivity of the saturated soil extract (<i>EC_e</i>) increased three times with <i>Gw</i> irrigation compared to <i>Rw</i> (current practices). Blended and alternate irrigation scenarios showed a 21 and 28% reduction in <i>EC_e</i>, respectively, compared to <i>Gw</i>. Irrigation water quality substantially impacted site-specific actual basal (<i>K_{cb act}</i>) and single (<i>K_{c act}</i>) crop coefficients of grapevine. Threshold leaching efficiency estimated in terms of the salt mass leached vs. added (<i>LE_s</i>; kg/kg) for salinity control (<i>LE_s</i> > 1) was achieved with <i>LFs</i> of 0.07, 0.12, 0.12, and 0.15 for the <i>Rw</i>, <i>Mix</i>, <i>Alt</i>, and <i>Gw</i> irrigations, respectively. Applying annual leaching irrigation (30 mm) before bud burst (spring) in the Mix and Alt with <i>Rw</i> and <i>Gw</i> scenarios was found to be the best strategy for managing irrigation-induced salinity in the root zone, lowering the <i>EC_e</i> to levels comparable to irrigation with <i>Rw</i>. Modeling scenarios suggested that judicious use of water resources and continuous root zone monitoring could be key for salinity management under adverse climate and low water allocation conditions.