Deficit Irrigation of Cabernet Sauvignon and Tempranillo: Impacts on Vine Growth, Yield, and Berry Composition

Field experiments were implemented in the 2010 season to contrast the impact of varied deficit irrigation regimes on vine development and fruit composition in Tempranillo and Cabernet Sauvignon. A similar randomized split-plot design was imposed at each site with three treatment replicates. Soil textures range from deep gravelly loam (> 5 feet) to silty clay loam soils (< 3 feet). The late winter and early spring weather conditions across the Southern Oregon region required some adjustment in the original irrigation protocols. Initiation of irrigation was delayed due to the cool and wet soil conditions. Based on the site specific weekly ETo and canopy width, each cooperator maintained the following irrigation treatments: (SD-35) initiate irrigation at 35 percent of ETc for the entire season; (RDI-35) initiate irrigation at 35 percent ETc until veraison, then 70 percent ETc until harvest; (SD-70) initiate irrigation at 70 percent ETc until harvest; and (RDI-75) initiate irrigation at 70 percent ETc until veraison, then 35 percent ETc to harvest. Fruit chemistry analysis continues at the time of this report in collaboration with the Dept. of Chemistry at Southern Oregon University. All members of this project agree that the atypical weather conditions in 2010 were an important factor having strong influence on the development and degree of water stress imposed in all treatments. Irrigation and crop level adjustments had variable impacts on leaf water potential, yield, Brix, pH, titratable acidity (TA), and leaf nutrition. Deficit irrigation treatments had a greater impact on Tempranillo in contrast to Cabernet. Irrigation and thinning had impact on fruit chemistry and ripening early, but by harvest these effects were muted and more variable. Beyond differences due to site, differences in crop level had greater, though variable impacts on fruit chemistry at intervals closer to veraison than harvest. At harvest there were few significant differences in Brix, pH, and TA due to irrigation, crop level, or the interaction of the two. Crop thinning generally had a greater impact on Brix (higher) closer to veraison than at harvest. Sugar accumulation was greatest in earlier ripening Tempranillo in comparison to the very late (under 2010 conditions) Cabernet crops at both sites. Acidity measures were also higher in Cabernet at harvest, and generally the deep soil site that produced both Tempranillo and Cabernet had lower fruit acidity than the shallow soil sites from 2 weeks post-veraison to harvest. Preliminary analyses surprisingly suggest that berry weight may have been greater in 35 percent deficit treatments, and greater in RDI treatments in contrast to SD treatments. Irrigation had a significant effect on many vine nutrients, although Tempranillo and Cabernet responded differently. Higher concentrations of N and other macronutrients in Tempranillo leaves from 35 percent deficit irrigation treatments may not be entirely due to growth or vigor ?dilution? effects. In contrast Cabernet often had higher macronutrient concentration with 75 percent deficit irrigation. We are still amassing and analyzing data to further our interpretation of 2010 experiments and will have a comprehensive final project report this spring.