Response of Riesling Grapes and Wine to Temporally and Spatially Heterogeneous Soil Water Availability

Background and goals Regulated deficit irrigation (RDI) and partial rootzone drying (PRD) have produced divergent viticultural and enological outcomes when implemented in vineyard settings, with most research focused on red wine grape cultivars. The goal of this work was to assess the suitability of RDI and PRD for producing high-quality grapes for white wine production in arid climates. Methods and key findings We conducted a three-year field trial with Riesling winegrapes to compare RDI and PRD with a fully irrigated control in southeastern Washington. Irrigation scheduling was based on soil moisture thresholds depending on vine phenology. We measured irrigation water supply, soil and plant water status, canopy size and density, yield components, and fruit and wine composition. Both RDI and PRD conserved irrigation water but reduced yield. While RDI saved more water than PRD, it reduced canopy size relative to the control. The irrigation methods did not affect basic fruit composition, but small differences in preveraison plant water status attained through differential irrigation resulted in notable differences in wine volatile profiles and, to a lesser degree, phenolic composition. Conclusions and significance This study highlights the potential of different irrigation methods to shape wine style in the vineyard through temporal and spatial manipulation of soil water availability. The "optimum" irrigation approach for white wine grapes should integrate the trade-off between management complexity and costs, reductions in water supply and yield, and gains in wine quality or changes in wine style.