Water Use of Wine Grapes in the Temecula Grape Region of California -Validation
The third (but last) of a four-year study to determine vine water use and effects of various irrigation amounts imposed either at bloom or veraison in the Temecula region was completed during the 1999-growing season. Calculated vine water use (ETc) from budbreak, March 25 to harvest September 24th, was 19.4 inches (1162 gal. Per vine). Applied water from the first irrigation (10 May) to harvest was 17.5 inches (1053 gal. per vine). A measure of vine water status (midday leaf water potential indicated that close to harvest these values were very similar to those recorded in 1998. Midday leaf water potential for the 25, 50, 75, 100 and 125%irrigation treatments were approximately -1.45, -1.35, -1.15, -0.95 and -0.9 MPa, respectively, each year. The application of differing amounts of water and time the treatments were imposed affected berry size and composition. Irrigation applications at the lowest amounts (25%of estimated ETc) reduced berry size by 32%when the treatments were imposed at bloom but less so when they were imposed at veraison. There was a significant interaction between irrigation amount and time the treatments were imposed. Maximum size resulted from irrigation amounts at 75 to 100%of estimated full vine water use. There were significant differences among irrigation treatments with regard to titratable acidity but not with soluble solids or pH. However, soluble solids tended to decrease as applied water increased. The time of irrigation applications did significantly affect pH and titratable acidity of the berries. There was a significant interaction between irrigation amounts and time of treatment imposition with regard to yield. Yield averaged across all treatments was approximately 8.1 tons per acre. Wines were made by the Callaway winery in 1998 as a function of irrigation amount and time of irrigation and assessed by myself and Callaway’s wine makers and vineyard personnel. Most individuals preferred wines made from application amounts of 75 and 100%of full ET. Based upon this tasting, wine was not made from the 25 or 50%irrigation amounts in 1999. Pruning weights were not taken after the 1999-growing season as the vineyard being used was severely affected by Pierce’s Disease. This also is the reason that the irrigation trial will not be conducted in the 2000-growing season.