Water Use of Cabernet Sauvignon Grafted onto Three Rootstocks in a Vineyard

A study was initiated in a Cabernet Sauvignon vineyard to determine the applicability of crop coefficients and deficit irrigation factors developed in a Chardonnay vineyard located in the Carneros district of Napa Valley at other locations, on different cultivars/rootstocks and row directions. The three rootstocks used in the trial were 5C, 110R and 3309C. Potential ET (ET0) from budbreak (23 March) until 20 September, 1998 was 802 mm (31.6 inches). Estimated full ET of the vines was determined by multiplying weekly ET0 by the crop coefficients developed in Carneros. Water use at 100%of estimated ETC between the above two mentioned dates was equivalent to 123 gallons per vine (321 mm or 12.6 inches based upon actual area allotted per vine in the vineyard). 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 interaction (irrigation treatment by rootstock) effects on all berry parameters measured on 28 September. Berry weight was maximized at irrigation amounts from 75 to 100%of ETC while the rootstock 5C had the largest berries. Soluble solids decreased, pH decreased and titratable acidity increased as applied water amounts increased. The pH was highest for the 110R rootstock and the TA was higher for both the 5C and 110R rootstocks compared to the 3309C rootstock. Vines receiving no applied water had the lowest yields followed by the 0.25 irrigation treatment. There were no significant differences in yield among the remaining four irrigation treatments. Wines were made as a function of irrigation treatment. TA and color intensity tended to decrease and pH and potassium increased in the wine as the amount of applied water increased. Pruning weight increased as the amount of applied water increased. Vines on the 5C rootstock had the highest pruning weights when comparisons among the rootstocks were made.