The last year of a three-year study was completed in a Cabernet sauvignon near Oakville in 2000. The objective was to determine the applicability of crop coefficients developed using Chardonnay in different vineyard with different cultivars, rootstocks and row directions. The three rootstocks used in the trial were 5C, 110R and 3309C. Potential ET (Eto) from budbreak (3 April) until harvest (21 September) was 875 mm (34.4 inches). Estimated full ET of the vines was determined by multiplying weekly Eto by the crop coefficients developed in Carneros. Water use at 100%of estimated Etc between the above two mentioned dates was equivalent to 209 gallons per vine (450 mm or 17.7 inches). Applied water in 2000 was equivalent to 187 gallons per vine.
Irrigation treatments at the vineyard were fractions (0, 0.25, 0.5, 0.75, 1.0 and 1.5) of estimated full Etc. Prior to harvest midday values of leaf water potential for the irrigation treatments at 100%of Etc or greater were less negative than ?1.0 Mpa. Vines that were deficit irrigated had midday leaf water potential values more negative than ?1.0 Mpa. There were significant irrigation and rootstock treatment effects on berry weight measured on 12 September. Berry weight was maximized at irrigation amounts from 75 to 100%of Etc while the rootstock 5C had the largest berries. There were no differences in soluble solids among treatments on the sample date. Rootstock had no significant effect on Ph and titratable acidity (TA). However, TA tended to increase as applied water amounts increased. Vines receiving no applied water or applied water at 0.25 Etc had the lowest yields. Vines receiving 75%of estimated Etc had the highest yield in 2000 (equal to 5.25 tons per acre). Wines were made as a function of irrigation treatment using fruit from all rootstocks. Wine color intensity and the total wine phenols index decreased as the amount of applied water increased. Two tasting panel sensory analyses indicated a preference for wine made from the 0.75 Etc treatment.
Over the three-year course of the experiment, berry weight was maximized at the 0.75 ETc irrigation treatment. This result is similar to studies I?ve conducted at other locations on wine grapes in the coastal valleys of California and on raisin and table grapes in the San Joaquin Valley. Pruning weights and yield were generally highest for the 0.75 ETc treatment in this study. Both parameters leveled off at applied water amounts above this treatment level. Yields of vines receiving no applied water, 0.25 ETc and 0.5 ETc were 66, 77 and 96%of the maximum yield, respectively. The results indicate that one could deficit irrigate this particular vineyard and have minimal effects on productivity, while increasing water use efficiency and providing beneficial effects on fruit quality.
PDF: Water Use of Cabernet Sauvignon Grafted onto Three Rootstocks in a Vineyard Near Oakville in the Napa Valley: Validation of Crop Coefficients and Regulated Deficit Irrigation Factors Developed in the Carneros District on Chardonnay