Geraldine Diverres* and Markus Keller
*Washington State University, 24106 N Bunn Road, V&E, Prosser, WA, 99350 (r.diverresnaranjo@wsu.edu)

Regulated deficit irrigation (RDI) is a common irrigation strategy for winegrape pro­duction in many regions, including eastern Washington. In addition to the potential to improve water use efficiency, the adoption of this technique usually favors quality attributes associated with red wines. This, added to a lack of specific irrigation guide­lines for white wine grapes, can lead to mismanagement and suboptimal fruit quality. We tested the performance of Riesling in response to RDI and partial rootzone drying (PRD) for high-end white wine grape production. Fully irrigated vines (FULL) were used as a control. Soil moisture and vine water status were monitored to determine the effect of irrigation regimes on growth, yield, sun exposure, and fruit composition over three years in a research vineyard in Prosser, WA. Our results support the notion that PRD could save up to 30% irrigation water while maintaining canopy growth (shoot length) and vine size (pruning weight). Unlike PRD, RDI resulted in smaller canopies, reduced vine size, and increased sun exposure of the clusters. Yields were similar between PRD and RDI. Fruit total soluble solids, pH, and titratable acidity did not differ among the three irrigation treatments. However, the higher fruit sun exposure in RDI might increase the bitterness of the resulting wines. To determine whether higher levels of sun exposure promoted the accumulation of compounds re­lated to bitterness, wines were made and will be evaluated at the WSU Wine Science Center to quantify phenolic composition. As increased levels of water stress and sun exposure may be counterproductive for aromatic grapes like Riesling, PRD has the potential to conserve water and maintain white wine grape quality in arid climates.

Funding Support: NSF/USDA Cyber Physical Systems Program and the Washington State Grape and Wine Research Program