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Williams L.E.,University of California at Davis | Williams L.E.,University of California Kearney Research and Extension Center
Australian Journal of Grape and Wine Research | Year: 2010

Background and Aims: It is commonly thought that grapevine rootstocks vary in their tolerance to drought. This study examined the interaction between various applied water amounts and productivity of Cabernet Sauvignon grafted onto five rootstocks. Methods and Results: The commercial vineyard used in this study was located along the central coastof California. The rootstocks used were Teleki 5C, 110 Ricter, 140 Ruggeri, 1103 Paulson and Freedom. Irrigation amounts ranged from 0.25 up to 1.25 of estimated vineyard evapotranspiration. Midday leaf water potential (Yl), was significantly affected by irrigation treatment but not by rootstock. There was a significant effect of irrigation treatment and rootstock on berry weight, number of bunches per vine and yield but no interaction between those two factors. The rootstock 5C had the lowest yield compared with the other rootstocks. Yield at the 0.25 irrigation level was approximately 62% of the yield at the 1.25 irrigation level across rootstocks. Irrigation treatment was the only factor that significantly affected soluble solids in the fruit. There was a significant interaction between rootstock and irrigation amount on pruning weights. Berry weight, yield and pruning weights were linearly correlated with midday Yl across rootstock and year. Conclusions: The results indicate that the rootstocks producing greater yields at the highest applied water amounts also produced greater yields when deficit irrigated. Significance of the Study: Under both stressed and non-stressed conditions, the rootstocks with the highest yield were those with the greatest number of bunches. © 2010 Australian Society of Viticulture and Oenology Inc.

Williams L.E.,University of California Kearney Research and Extension Center
Australian Journal of Grape and Wine Research | Year: 2012

Aims: To determine the effects of applied water amounts at various fractions (0.2, 0.6, 1.0 and 1.4) of grapevine evapotranspiration on leaf gas exchange of Thompson Seedless grapevines. Methods and Results: Midday stomatal conductance (g s) decreased linearly as leaf water potential (Ψ l) and soil water content decreased. Leaf net CO 2 assimilation rate only decreased once midday Ψ l values were less than -1.0MPa and when ~50% of the soil water content at field capacity had been depleted. The mean seasonal midday A/g s ratio (intrinsic water use efficiency) was greatest for the 0.2 irrigation treatment and decreased as applied water amounts increased. Diurnal A and g s for vines irrigated at the 0.6 level or greater reached a maximum prior to midday remained constant thereafter before decreasing late in the afternoon, while those for vines that received less water decreased subsequent to the first measurement of the day. Conclusions: A and g s responded differently to vine and soil water statuses under the conditions of this study. There was no midday depression in either A or g s for vines irrigated at full evapotranspiration. Significance of the Study: The values of Ψ l, A and g s reported here would serve as criteria to indicate that vines were well watered. © 2012 Australian Society of Viticulture and Oenology Inc.

Williams L.E.,University of California Kearney Research and Extension Center
Journal International des Sciences de la Vigne et du Vin | Year: 2012

Aims: Leaf (Ψ1) and stem (Ψstem) water potentials were measured on grapevines to determine the effects of shoot location on both methods to assess vine water status. Methods and results: Cabernet-Sauvignon and Merlot used in this study were grown at two locations in California. Measurements were taken at midday in July (Merlot) and at two times of the day (morning and afternoon), on two dates in August (Cabernet-Sauvignon). Measurements of Ψl and Ψstem, stomatal conductance and transpiration were taken on shoots entirely exposed to direct solar radiation or on shoots totally in the shade at the times of measurement. There were significant differences (P < 0.05) between Ψl and/or Ψstem measured on shoots exposed to direct solar radiation and those in the shade. Both Ψl and Ψstem were significantly greater on the shoots exposed to direct sunlight compared to those in the shade. There was no significant difference between Ψl measured on shaded leaves and Ψstem determined on the fully exposed shoots. Conclusions: Regardless of method used, water potentials were highly correlated with stomatal conductance measured on leaves in direct sunlight at the same time. All means of measuring grapevine water potential used in this study were highly correlated with one another. Significance and impact of the study: The data indicate that any of the techniques used in this study would be a sensitive indicator of vine water status and that the Ψ of shaded leaves would be an alternative to the measurement of Ψstem. © Vigne et Vin Publications Internationales.

Williams L.E.,University of California at Davis | Williams L.E.,University of California Kearney Research and Extension Center
Irrigation Science | Year: 2012

A study was conducted in the San Joaquin Valley of California on Merlot to determine the interaction of applied water amounts [at 0.4, 0.8, and 1.2 of estimated vineyard evapotranspiration (ET c)] and leaf removal (at berry set or veraison) in the fruiting zone on productivity. Shaded area was measured beneath the canopy of the 1.2 irrigation treatment at solar noon throughout the study to provide an estimate of seasonal crop coefficients (K c). Vine water status was assessed across treatments and years by measuring midday leaf water potential (Ψ l). The maximum K c determined from the percent shaded area was 0.7 at the row spacing of 3.66 m and canopy type that developed a "California Sprawl." Irrigation treatment had a significant effect on midday Ψ l and no such effect for leaf removal. Clusters exposed to direct solar radiation had significantly higher temperatures and lower cluster Ψ than clusters in the shade. Irrigation treatment had a significant effect on berry weight, soluble solids, and titratable acidity. Yields of vines significantly increased as applied water amounts increased. In this wine grape production area, profitability is dependent upon yield. This study provided a reliable estimate of ET c and applied water amounts to maximize yield. © 2012 Springer-Verlag.

Williams L.E.,University of California at Davis | Williams L.E.,University of California Kearney Research and Extension Center
American Journal of Enology and Viticulture | Year: 2014

A study was conducted in a Chardonnay vineyard located in the Carneros district of Napa Valley to derive vineyard evapotranspiration (ETc) and seasonal crop coefficients (Kc) values. The vineyard was planted on 2.13 m rows, using a vertical shoot-positioned trellis. Vineyard ETc was measured using the soil water balance method. Soil water content (SWC) was measured in one-fourth of an individual vine's soil profile (six access tubes per site) to a depth of 2.75 m. In addition, vines were irrigated with applied water amounts at 0.25, 0.5, 0.75, 1.0, and 1.25 of estimated vineyard ETc. Vineyard ETc the first year of the study was ~400 mm. Thereafter calculated vineyard Etc (the product of reference ET [ETo] and the Kc) ranged from 346 to 503 mm per season. Midday leaf water potential (Ψl), leaf net CO2 assimilation rate (A), and stomatal conductance (gs) were used to indirectly validate estimated Etc (to determine that vines were not stressed for water) and the derived Kc values. Midday Ψl, A, and gs were linearly related with applied water amounts and SWC across irrigation treatments and years. The diurnal measurements of A and gs resulted in differences among irrigation treatments, from early morning until late afternoon, with significant differences among treatments dependent upon actual applied water amounts. The results from this study are the first in which vineyard ETc has been measured on vines grown at a cool vineyard site in California. Estimates of ETc from this study would be valid for a vineyard with a row spacing of 2.13 m and a canopy vertically positioned using a maximum Kc of 0.74. © 2014 by the American Society for Enology and Viticulture. All rights reserved.

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