Frost hardiness of irrigated and fertigated 'Chardonnay' grapevines

The purpose of this study was to determine if irrigation and/or fertigation, practices used to improve grape production and fruit and wine quality in the Eger wine district of Hungary, would affect vine cold hardiness. Cordon trained 'Chardonnay' vines with two different pruning levels were irrigated or fertigated from anthesis until 4 weeks prior to harvest. Changes in soil moisture tension were monitored with tensiometers and soil and leaf nutrient analyses were determined at anthesis, veraison and harvest. Different methods were used to characterize dormancy of buds and canes: (1) Microwave technique measuring free and bound water contents in canes, (2) Analysis of soluble sugars in canes and (3) Differential thermal analysis determining low temperature exotherm (LTE) values. Yields of irrigated or fertigated vines exceeded that of the control from 25-50% and 12-55% in 2002 and 2003, respectively. Both irrigation and fertigation slightly delayed cane ripening (about 1 month) compared to the control. This was reflected in the ratio of bound to total water content of the xylem, but the differences disappeared by the beginning of December. There were no significant differences in soluble sugar content (glucose, fructose sucrose, and raffinose) among treatments. The LTE temperatures of the different treatments also did not detect a considerable decrease in freezing tolerance. The results indicate that freezing tolerance of 'Chardonnay' grapevines is not adversely affected by irrigation, fertigation or pruning level under the conditions of this study.