Influences of Direct Root-Zone Deficit Irrigation on Root Distribution and Wine Grape Production in Pacific Northwest.

Direct root-zone (DRZ) deficit irrigation is an emerging strategy to enhance water conservation and fruit quality in Pacific Northwest vineyards. After two growing seasons, DRZ has demonstrated advantages in regulating plant water stress and improving crop water use efficiency, while balancing both yield and quality of wine grapes. DRZ, by delivering water to the lower soil profile, has led to deeper root growth and creation of a dry zone in the upper soil profile which limits water availability for weed growth under Mediterranean growing conditions typical in the PNW. Two experiments were conducted in commercial vineyards to investigate influences of DRZ applied as season-long deficit irrigation on root traits, grape production, and fruit quality compared with commercial surface drip irrigation. Irrigation rates of DRZ were applied at 60, 30, and 15 percent of full commercial rate applied as surface drip. DRZ was delivered subsurface at 30, 60, and 90 cm depths by two irrigation methods (constant versus pulse). Total irrigation amount significantly influenced root length, volume, and distribution, as well as fruit yield; however, quality of grapes was enhanced under concomitant reduction in seasonal water delivery amounts. No significant differences in grape yield were attributed to any particular depth of DRZ delivery. Compared with commercial surface drip irrigation, root-zone deficit irrigation strategy advanced crop water use efficiency (grape yield: water applied) in direct correlation with reduced amounts of water applied. After two growing seasons, DRZ deficit irrigation shows promise for water conservation and enhancement of wine grape quality. We expect that this irrigation strategy could be extended to other perennial specialty crops such as apples, cherries, and hops.