Water Use of Wine Grapes Along the Central Coast of California – Validation

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 March 9 and September 20 at Gonzales, Paso Robles and Edna Valley was 754, 898 and 923 mm (29.7, 35.4 and 36.3 inches), respectively. Estimated full ETC was determined by multiplying weekly ET0 by the crop coefficient developed in Carneros. Calculated water use at 100%of ETC between the above two mentioned dates was equivalent to 385, 456 and 378 gallons per vine at Gonzales, Paso Robles and Edna Valley, respectively, while applied water at the same locations was 353, 391 and 276 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 generally had the predominate effect on berry pH. Titratable acidity significantly increased as applied water increased at the Gonzales site but not at the other two vineyard locations. There were no significant effects of irrigation treatments on titratable acidity at Paso Robles. Yields tended to increase at all locations with an increase in applied water. The maximum yields at each location occurred at the 125%irrigation treatment when averaged across rootstocks. Rootstock had a significant effect at all locations on final yield. Wine lots were made as a function of irrigation treatment (using the 5C rootstock) at the Gonzales and Paso Robles sites. Pruning weights were taken at the Gonzales and Paso Robles sites. Both irrigation and rootstock treatments had a significant effect on pruning weights, but there were no interactions between the two.