Modeling Grapevine Water Use

Data were collected on Thompson Seedless grapevines grown in a weighing lysimeter to refine a model of vine water use and then compare those results with actual water use. The model was dependent upon the interception of sunlight on each of the three canopy surfaces (top, north and south; row direction east to west) and the relationship between light and stomatal conductance. The canopy also was divided into sunlit and shaded leaf areas. Measures of total vine leaf area, shaded area and leaf area index (LAI) were also measured several times during the growing season. Solar and net radiation, vapor pressure and wind speed were measured above the canopy of the vines within the lysimeter. Once the necessary environmental data had been collected on a specific day and canopy conductance (gc) had been modeled, canopy resistance (l/gc) and aerodynamic resistances were inserted into a resistance-energy balance equation to calculate vine water use. There was a linear relationship between total leaf area per vine and shaded area per vine. As leaf area increased from 2 to 25 m2 per vine, shaded area increased from 0.8 to just less than 5 m2 per vine. The LAI (m2 leaf area m”2 shaded surface area) of the vines in the lysimeter increased up until total vine leaf area was 15 m2 per vine at which time it leveled off (at approximately 5.6 m2 m”2) with further increases in whole vine leaf area. There were linear relationships (r ‘s greater than 0.9) between vine water use and shaded area per vine and {aed9a53339cdfc54d53cc0c4af03c96668ab007d9c364a7466e3349a91bf0a23} shaded area per unit land area. In addition, the crop coefficient (kc) and total vine leaf area also were linearly related to vine water use (i^’s approximately 0.88). Modeled water use and actual water use on three dates (August 4 and 12 and September 6) late in the growing season were compared with one another. The two earlier dates were chosen as vine leaf area differed from August 4 to 12 due to cane cutting on August 8. Modeled and actual water use on August 4 was 12.3 and 12.28 mm, respectively. The model overestimated water use on 12 August and 6 September by 5.7 and 7.8{aed9a53339cdfc54d53cc0c4af03c96668ab007d9c364a7466e3349a91bf0a23}, respectively. On all dates tested, the model underestimated water use early in the morning and overestimated water use late in the afternoon. To obtain the above results, it was determined that canopy conductance was responding to VPD and therefore, gc was made a function of VPD (when the VPD was greater than 2.0 kPa.). Due to the lateness in which monies to conduct this study were received, water use was not modeled earlier in the growing season because the appropriate measures of canopy light interception had not been measured. The results collected in 1998 are promising but indicate that further refinement is needed both at the leaf and canopy levels.

Water Use of Cabernet Sauvignon Grafted onto Three Rootstocks in a Vineyard

A study was initiated in a Cabernet Sauvignon vineyard to determine the applicability of crop coefficients and deficit irrigation factors developed in a Chardonnay vineyard located in the Carneros district of Napa Valley at other locations, on different cultivars/rootstocks and row directions. The three rootstocks used in the trial were 5C, 110R and 3309C. Potential ET (ET0) from budbreak (23 March) until 20 September, 1998 was 802 mm (31.6 inches). Estimated full ET of the vines was determined by multiplying weekly ET0 by the crop coefficients developed in Carneros. Water use at 100{aed9a53339cdfc54d53cc0c4af03c96668ab007d9c364a7466e3349a91bf0a23} of estimated ETC between the above two mentioned dates was equivalent to 123 gallons per vine (321 mm or 12.6 inches based upon actual area allotted per vine in the vineyard). Irrigation treatments at the vineyard were fractions (0, 0.25, 0.5, 0.75, 1.0 and 1.5) of estimated full ETC. Prior to harvest midday values of leaf water potential for the irrigation treatments at 100{aed9a53339cdfc54d53cc0c4af03c96668ab007d9c364a7466e3349a91bf0a23} of ETC or greater were less negative than -1.0 MPa. Vines that were deficit irrigated had midday leaf water potential values more negative than -1.0 MPa. There were significant interaction (irrigation treatment by rootstock) effects on all berry parameters measured on 28 September. Berry weight was maximized at irrigation amounts from 75 to 100{aed9a53339cdfc54d53cc0c4af03c96668ab007d9c364a7466e3349a91bf0a23} of ETC while the rootstock 5C had the largest berries. Soluble solids decreased, pH decreased and titratable acidity increased as applied water amounts increased. The pH was highest for the 110R rootstock and the TA was higher for both the 5C and 110R rootstocks compared to the 3309C rootstock. Vines receiving no applied water had the lowest yields followed by the 0.25 irrigation treatment. There were no significant differences in yield among the remaining four irrigation treatments. Wines were made as a function of irrigation treatment. TA and color intensity tended to decrease and pH and potassium increased in the wine as the amount of applied water increased. Pruning weight increased as the amount of applied water increased. Vines on the 5C rootstock had the highest pruning weights when comparisons among the rootstocks were made.

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{aed9a53339cdfc54d53cc0c4af03c96668ab007d9c364a7466e3349a91bf0a23} 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{aed9a53339cdfc54d53cc0c4af03c96668ab007d9c364a7466e3349a91bf0a23} 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{aed9a53339cdfc54d53cc0c4af03c96668ab007d9c364a7466e3349a91bf0a23} 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.

Water Use of Wine Grapes In the Temecula Grape Region of California

The second 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 1998-growing season. Calculated vine water use (ETC) from budbreak, 9 March, to the end of the growing season, 26 October, was 23.9 inches (1,399 gal. per vine). Applied water from the first irrigation (28 April) to harvest was 17.2 inches (906 gal. per vine). A measure of vine water status (midday leaf water potential) indicated that close to harvest, our estimates of full vine water were pretty much on schedule. The application of differing amounts of water and time the treatments were imposed affected berry size and composition. Irrigation applications at the lowest amounts (25{aed9a53339cdfc54d53cc0c4af03c96668ab007d9c364a7466e3349a91bf0a23} of estimated ETC) reduced berry size by 14{aed9a53339cdfc54d53cc0c4af03c96668ab007d9c364a7466e3349a91bf0a23} when the treatments were imposed at bloom but less so when they were imposed at veraison. Maximum size resulted from irrigation amounts at 75 to 100{aed9a53339cdfc54d53cc0c4af03c96668ab007d9c364a7466e3349a91bf0a23} of estimated full vine water use. There were differences among irrigation treatments with regard to berry composition (soluble solids, pH and titratable acidity [TA]). Higher soluble solids were obtained as irrigation amounts decreased and higher TA as irrigation amounts increased. There was a significant interaction between irrigation amounts and time of treatment imposition with regard to yield. Yield averaged across all treatments was approximately 6.2 tons per acre. Pruning weights increased significantly as the amount of water applied increased. Wines were made by the Calloway winery in 1998 and are currently being assessed by winemakers in the Temecula Valley.

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

A study was initiated in two 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. Since the amount of money received from the American Vineyard Foundation was only 44{aed9a53339cdfc54d53cc0c4af03c96668ab007d9c364a7466e3349a91bf0a23} of that requested, data were only collected in a Chardonnay vineyard located in Monterey County and a Cabernet Sauvignon vineyard east of Paso Robles. No data were collected at the other proposed site (a Chardonnay vineyard located in the Edna Valley) nor were data collected in all blocks of the two above cited vineyards. Irrigation treatments began on 6 May in the Chardonnay vineyard with a total of 305 gallons of water (10.2 inches) applied per vine up to harvest (Oct 1) for those irrigated at 100{aed9a53339cdfc54d53cc0c4af03c96668ab007d9c364a7466e3349a91bf0a23} of estimated full ET. Irrigation treatments commenced 12 June at the Paso Robles site with a total of 321 gallons applied per vine to those receiving 100{aed9a53339cdfc54d53cc0c4af03c96668ab007d9c364a7466e3349a91bf0a23} of estimated full ET. Maximum berry weight was obtained at approximately the full ET treatments at both locations. Application of water at amounts greater than full ET did not increase berry size. There were no significant effects of irrigation treatments on soluble solids or pH at the Monterey site. Titratable acidity increased as applied water increased at that site. As applied water increased at the Paso Robles site, soluble solids decreased. There were no significant effects of irrigation treatments on titratable acidity at Paso Robles. Maximum yields at the Monterey site were obtained at the 125{aed9a53339cdfc54d53cc0c4af03c96668ab007d9c364a7466e3349a91bf0a23} irrigation treatment when averaged across rootstocks. This was probably due to the fact that the vines at that site were inadvertently stressed early in the season (during bloom/berry set). Maximum yields at the Paso Robles site were obtained at the 50{aed9a53339cdfc54d53cc0c4af03c96668ab007d9c364a7466e3349a91bf0a23} irrigation treatment for two of the rootstocks, at the 75{aed9a53339cdfc54d53cc0c4af03c96668ab007d9c364a7466e3349a91bf0a23} treatment for another and at 100{aed9a53339cdfc54d53cc0c4af03c96668ab007d9c364a7466e3349a91bf0a23} of estimated full ET for the remaining two rootstocks. These results were probably due to the fact that the treatments were not imposed at the Paso Robles site until after berry set had occurred during the 1997 growing season. Wine lots were not made after harvest in 1997.

Water Use and Effects of Deficit Irrigation on Chardonnay Grapevines Grown in the

A study was conducted to determine the water use or vineyard evapotranspiration (ET) of Chardonnay grapevines subsequent to vineyard establishment. ET is the combined loss of water by evaporation from the soil and transpiration by the vine. The experimental vineyard is located in the Carneros District of Napa Valley. In addition, the vines were grafted onto two different rootstocks (110R and 5C) to determine if there are differences in water use between them. Lastly, five irrigation treatments were imposed to determine the effects of both under- and over-irrigation on vine physiology and growth and wine quality. Vine water use was determined by measuring soil water depletion and the addition of water during an irrigation. Soil water content was measured with a neutron probe at eight sites throughout the vineyard, four sites per rootstock. Vineyard water use in 1997 at full ET (i.e. water applications equal to vine water use) was approximately 470 mm (18.5 inches). Deficit irrigation of vines resulted in the depletion of soil water, the amount dependent upon water application amounts. There has been no difference in water use between the two rootstocks. Water applications less than full ET resulted in more negative leaf water potentials and lower stomatal conductance and photosynthesis. The percent reduction was a function of the amount of water applied. There were significant reductions in berry size for vines that were deficit irrigated in 1997. There have been no differences among irrigation treatments with regard to juice pH. Titratable acidity increased with increasing water applications. There were minor differences in berry composition among the rootstocks in 1997; however, there were no significant interactions among rootstocks and irrigation treatments. Experimental wines made in 1997 are currently being analyzed.

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{aed9a53339cdfc54d53cc0c4af03c96668ab007d9c364a7466e3349a91bf0a23} of estimated ETC) reduced berry size by 34{aed9a53339cdfc54d53cc0c4af03c96668ab007d9c364a7466e3349a91bf0a23} 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{aed9a53339cdfc54d53cc0c4af03c96668ab007d9c364a7466e3349a91bf0a23} (or lower) of estimated full vine water use. Maximum size resulted from irrigation amounts at 100{aed9a53339cdfc54d53cc0c4af03c96668ab007d9c364a7466e3349a91bf0a23} 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{aed9a53339cdfc54d53cc0c4af03c96668ab007d9c364a7466e3349a91bf0a23} 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.

Water Use and Effects of Deficit Irrigation on Chardonnay Grapevines

A study is being conducted to determine the water use or vineyard evapotranspiration (ET) of Chardonnay grapevines subsequent to vineyard establishment. ET is the combined loss of water by evaporation from the soil and transpiration by the vine. The experimental vineyard is located in the Carneros District of Napa Valley. In addition, the vines are grafted only two different rootstocks (110R and 5C) to determine if there are differences in water use between them. Lastly, five irrigation treatments were imposed to determine the effects of both under and over-irrigation on vine physiology and growth and wine quality. Vine water use is determined by measuring soil water depletion and the addition of water during an irrigation. Soil water content is being measured with a neutron probe at eight sites throughout the vineyard, four sites per rootstock. Vineyard water use in 1996 at full ET (i.e., water applications equal to vine water use) were approximately 470 mm (18.5 inches). Deficit irrigation of vines resulted in the depletion of soil water, the amount dependent upon water application amounts. To date there has been no difference in water use between the two rootstocks. Water applications less than full ET result in more negative leaf water potentials and lower stomatal conductance and photosynthesis. The percent reduction is a function of the amount of water applied. There are highly significant correlations between the grapevine’s water status and soil water content when measured on the same day. There were significant reductions in berry size for vines that were deficit irrigated in 1996. There has been no differences among irrigation treatments with regard to juice pH. Titratable acidity increased with increasing water applications. There were minor differences in berry composition among the rootstocks in 1996; however, there were no significant interactions among rootstocks and irrigation treatments. Experimental wines made in 1996 are currently being analyzed. Preliminary results indicate a preference for wines made from the 50{aed9a53339cdfc54d53cc0c4af03c96668ab007d9c364a7466e3349a91bf0a23} to full ET irrigation treatments.

Water Use and Effects of Deficit Irrigation on Chardonnay

A study is being conducted to determine the water use or vineyard evapotranspiration (ET) of Chardonnay grapevines subsequent to vineyard establishment. ET is the combined loss of water by evaporation from the soil and transpiration by the vine. The experimental vineyard is located in the Carneros District of Napa Valley. In addition, the vines are grafted onto two different rootstocks (110R and 5C) to determine if there are differences in water use between them. Lastly, five irrigation treatments were imposed to determine the effects of both under- and over-irrigation on vine physiology and growth and wine quality. Vine water use is determined by measuring soil water depletion and the addition of water during an irrigation. Soil water content is being measured with a neutron probe at eight sites throughout the vineyard, four sites per rootstock. Vineyard water use in 1994 and 1995 at full ET (i.e. water applications equal to vine water use) were approximately 470 mm (18.5 inches). Deficit irrigation of vines resulted in the depletion of soil water, the amount dependent upon water application amounts. To date there has been no difference in water use between the two rootstocks. Water applications less than full ET result in more negative leaf water potentials and lower stomatal conductance and photosynthesis. The percent reduction is a function of the amount of water applied. There are highly significant correlations between the grapevine’s water status and soil water content when measured on the same day. There were significant reductions in berry size for vines that were deficit irrigated in 1994 but not in 1995. The difference between the years was due to an irrigation event in 1995 at berry set that resulted in no stress among treatments for a period of approximately three weeks. There has been no differences among irrigation treatments with regard to juice pH. Titratable acidity increased with increasing water applications both years. There were minor differences in berry composition among the rootstocks in 1995, however, there were no significant interactions among rootstocks and irrigation treatments. Experimental wines made in 1994 and 1995 are currently being analyzed. Preliminary results indicate a preference for wines made from the 75{aed9a53339cdfc54d53cc0c4af03c96668ab007d9c364a7466e3349a91bf0a23} and full ET irrigation treatments.

Water Requirements During and After Vineyard Establishment for Chardonnay Grapevines Grown in the Carneros District

ABSTRACT: A study is being conducted to determine the water use of Chardonnay grapevines grown in the Carneros District of Napa Valley during vineyard establishment. Vineyard water use was determined by measuring soil water content with a hydroprobe and measuring applied water and effective rainfall. The arrangement of access tubes at each site allowed us to quantify the amount of water within the soil profile. A decrease in soil water content would indicate that irrigation was not meeting the water requirements of the vines while an increase in soil water content would indicate that irrigation was greater than vineyard evapotranspiration (ET). The soil water content decreased from budbreak until the middle of September and remained constant after that. This would indicate that applied water was less than vineyard ET. Soil water supplied approximately 38{aed9a53339cdfc54d53cc0c4af03c96668ab007d9c364a7466e3349a91bf0a23} of the 316 mm (12.4 inches) of water used by the vines in that vineyard. Effective rainfall supplied 36{aed9a53339cdfc54d53cc0c4af03c96668ab007d9c364a7466e3349a91bf0a23} of the water used by the vines. The depth of water extraction from the soil profile extended to greater than 2.0 m (approximately 7 ft). Midday values of leaf water potential measured throughout the season were no more negative than -1.0 MPa (-10 bars) except when maximum, ambient temperatures were greater than 27°C (81°F) . The crop coefficient ranged from 0.2 to approximately 0.7, depending upon the time of year.