Water Use of Wine Grapes in the Temecula Grape Region of California – Validation

The first 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 1997 growing season. Calculated vine water use (ETC) from budbreak, 17 March, to the end of the growing season, 26 October, was 23.4 inches (1,406 gal. per vine). AppUed water from the first irrigation (28 April) to harvest was 15.3 inches (917 gal. per vine). Total applied water during the irrigation season (28 April to 26 October) was 21.6 inches (1,297 gal. per vine). A measure of vine water status (midday leaf water potential) indicated that close to harvest, our estimates of full vine water use may have been too much. This could have been due to the fact that the vines in this vineyard looked somewhat potassium stressed at that time and may not have used as much water if this had not occurred. The application of differing amounts of water and time the treatments were imposed affected both berry composition and final yield. Irrigation applications at the lowest amounts (25%of estimated ETC) reduced berry size by 34%when the treatment was imposed at bloom, compared to the maximum berry size obtained. When the treatments were imposed at veraison, there was no decrease in berry size until irrigation amounts were 50%(or lower) of estimated full vine water use. Maximum size resulted from irrigation amounts at 100%of estimated full vine water use. There were little differences among treatments with regard to berry composition (soluble solids, pH and titratable acidity [TA]). There were trends for higher soluble solids as irrigation amounts decreased when the treatments were imposed at bloom and higher T A as irrigation amounts increased for both the bloom and veraison dates of imposition. Yields tended to decrease for water application amounts less than full ET for the bloom time treatments and less than 75%of full ET for the verasion treatments. Yield averaged across all treatments was approximately 11 tons per acre. Pruning weights increased only slightly as the amount of water applied increased. No wines were made from the study last year. It is anticipated that wines will be made as a function of irrigation treatments in 1998.