Water Use of Wine Grapes Along the Central Coast of California – Validation of
A study was continued in three vineyards along the central coast of California to determine the applicability of crop coefficients and deficit irrigation factors established in a Chardonnay vineyard located in the Carneros district of Napa Valley at other locations. The vineyard sites were located at Gonzales in the Salinas Valley, Paso Robles and Edna Valley, south of San Luis Obispo. Potential ET (ET0) between budbreak and harvest at Gonzales, Paso Robles and Edna Valley was 997, 1023 and 959 mm (39.3, 40.3 and 37.7 inches), respectively. Estimated full ETC was determined by multiplying weekly ET0 by the crop coefficient developed in Carneros for 7-foot rows and then adjusted for row width at each vineyard. Calculated water use at 100%of ETC between the above two mentioned dates was equivalent to 402, 423 and 400 gallons per vine at Gonzales, Paso Robles and Edna Valley, respectively, while applied water at the same locations was 351, 337 and 353 gallons per vine. Irrigation treatments at each location were fractions (0.25, 0.5, 0.75, 1.0 and 1.25) of estimated full ETC. Maximum berry weight was obtained at irrigation amounts between 75 and 100%of estimated full ET treatments at all locations. Application of water at amounts greater than full ET did not significantly increase berry size. Soluble solids were significantly affected by irrigation treatments at all locations; the less amount of water applied the higher the °Brix. Rootstock and irrigation had an effect on berry pH. Titratable acidity was significantly affected by applied water amount as well as rootstock at all locations, however, there were no rootstock/irrigation interactions. Yields were not measured at the Gonzales site as the cooperator harvested the plots without prior notification. Rootstock had a significant effect on yield at the Edna Valley site. The rootstock 110R had the highest yield at that location followed by 5C while the lowest was Freedom. There was a significant interaction of rootstock and irrigation treatment on yield at the Paso Robles site. Yields of 5C and 110R tended to be maximized at the 0.75 irrigation treatment (leveling off with further increases in applied water) while yields of Freedom, 140 Ruggeri and 1103 Paulsen increased with more applied water. It should be pointed out that both 5C and 110R had delayed vegetative growth at the beginning of the 1999-growing season. It is unknown whether this was due to lack of soil moisture or to below average temperatures (or soil temperatures) early in the season. Pruning weights had not been measured as of the date this report was written.