Xiaochi Ma, Karen Sanguinet, and Pete Jacoby*
*Washington State University, P.O. Box 646420, 289 Johnson Hall, Pullman, WA 99164 (jacoby@wsu.edu)

Water for vineyard irrigation now faces potential limits in seasonally dry regions owing to multiple competing demands from other crops and unstable climatic patterns. Deficit irrigation has been proven effective in saving water, increasing water use efficiency while sustaining fruit yield, and enhancing grape quality for red wines. However, conventional surface deficit irrigation causes moisture loss through water evaporation and encourages weed growth, and grapevines may produce more shallow roots rather than distribute roots into deep soil, which can weaken their response to extreme drought and water shortage. Delivering a limited water supply directly into the deep root-zone by using subsurface microirrigation may be a good strategy to address these challenges. We hypothesize that limited water delivered directly into the middle and lower root-zone will help sustain grapevine growth and grape production, improve water use efficiency, and optimize biomass partitioning in grapevine. Using Cabernet Sauvignon as a model variety, we conducted both greenhouse and field experiments (2015 to 2017) to investigate the effects of direct root-zone deficit irrigation (DRZ) with different rates, depths, and water delivery methods (constant versus pulse) on grape production, grapevine growth, and root distribution. Total irrigation amount significantly influenced fruit yield, and grape quality was enhanced under concomitant reduction in seasonal water delivery amounts. No significant differences in grape yield were attributed to any irrigation depth and method of DRZ delivery; however, irrigation depth had a significant influence on root length, number, and distribution. Compared with commercial surface drip irrigation, DRZ improved photosynthesis capacity and advanced crop water use efficiency in direct correlation with the reduced amounts of water applied. Meanwhile, rates of biomass accumulation at different growing stages were variable, which must be considered for efficient irrigation management. After three growing seasons, DRZ shows promise for water conservation and enhancement of winegrape production.

Funding Support: WSDA Specialty Crop Block Grant Program; Northwest Center for Small Fruit Research; Western Sustainable Agriculture Research and Education Program (WSARE, USDA) Graduate Student Grant; Washington State Grape and Wine Research Program.