New technology for determining vine water status and controlling vineyard

We confirmed that ultrasonic acoustic emissions occur in field-grown grapevines subjected to water deficits. The appropriate sensor and frequency for adequate detection was determined. Although we can record acoustic emission rates in the field, we are not satisfied with the present sensor attachment. For Cabernet Sauvignon vines in the Lodi area, differences in the rate of acoustic emissions at the onset of veraison were easily resolved between vines receiving irrigation every other day and vines from which water was withheld up to that point. The rate of acoustic emissions from the stressed vines was two to five times greater than from the irrigated vines at midday. When water was withheld (at 50{aed9a53339cdfc54d53cc0c4af03c96668ab007d9c364a7466e3349a91bf0a23} veraison) from some vines for only six days, there were again large differences (up to five-fold) in the rate of acoustic emissions at midday. The results suggest that the water status of a vineyard may be estimated daily and automatically without grower labor input.

Influence of nitrogen fertilization and other vineyard cultural practices on the

Sauvignon blanc and Chardonnay grapevines grown at the North Oakville Experimental Vineyard (OEV) generally responded favorably to increased rate of nitrogen fenilization up to 90 lbs/acre as demonstrated by higher yield, shoot growth, pruning weight and total leaf area per vine. Differences in fruit composition between low and high nitrogen fertilization were relatively small. However, high N generally increased the pH, TA, malate, K, and arginine levels of must of both cultivars. The field fertilization did certainly improve the ability of the juices to ferment. Without the nitrogen additions, the juices took twice as long to ferment. Otherwise, the routine must and wine analyses show little differences.

Shoot positioning as a means of improving fruit composition, wine quality

Two replicated shoot positioning field trials were conducted from 1987 to 1990; one with Chardonnay, Sauvignon blanc and Cabernet Sauvignon vines at the Oakville Experimental Vineyard and the other with Chenin blanc vines at Davis. Chardonnay. Sauvignon blanc and Cabernet Sauvignon trial: The main conclusions obtained from the Chardonnay, Sauvignon blanc and Cabernet Sauvignon shoot positioning-hedging trial conducted at the Oakville Experimental Vineyard over a period of five years (1987 to 1990) may be summarized as follows. Conclusions are based on five-year averages. 1. Shoot positioning/hedging (SP) of Chardonnay and Sauvignon blanc increased crop yield by 4 to 5{aed9a53339cdfc54d53cc0c4af03c96668ab007d9c364a7466e3349a91bf0a23} or 0.4 tons/acre compared to no shoot positioning (NSP) and hedging (Tables 1 and 2). Shoot positioning and hedging did not effect the crop yield of Cabernet Sauvignon. 2. SP reduced the amount of direct light and increased the amount of indirect light (diffuse light) in the fruiting zone.

The Regulation of Fruit Growth, Fruit Composition, and Wine Composition by Water Management

This summary will constitute a brief overview of what we have learned about water stress in winegrape production in California. This project was designed to extend our initial study with hillside Cabernet franc and Sauvignon blanc (1984-1988) by extending our understanding of the role of vine water status in determining yield, fruit and wine composition, and wine sensory attributes. Experiments and sites were designed to test several questions including: whether vine water status can be readily controlled at different sites and soils (Carneros and Lodi areas); whether other important red winegrape varieties, Pinot noir and Cabernet Sauvignon, respond similarly to seasonal water deficits; whether water stress at veraison is particularly critical in determining the composition of harvested fruit; whether the changes in fruit composition caused by water stress are due directly to water stress or to indirect effects of changes in the cluster microclimate; and which specific flavor and aroma compounds are responsible for the sensory differences caused by water stress. We report that soil and vine water status is readily controlled in drip-irrigated vineyards of Pinot noir (Carneros) and Cabernet Sauvignon (Lodi). For the Pinot noir site, differences in water status of vines receiving the standard or a supplemented rate of irrigation were greater than we obtained in the hillside Cabernet franc and Sauvignon blanc we used in our earlier study. This shows that our earlier results can be extrapolated to valley floors and are not indicative only of hillside vineyards with shallow soils and high exposures. The results also show the utility of drip irrigation for control of vine water status and the prevalence of water deficits in winegrape production in the North Coast. Thus, many growers can control vineyard water status; we are working to identify how much stress should occur and when to meet grower and winemaker objectives. The results from three sites and four varieties over several seasons indicate some clear generalizations. Regulation of vine water status is effective in controlling fruitfulness, and many vineyards may be under-irrigated for maximum fruitfulness. Early season stress is more effective in decreasing berry size and fruitfulness in the following season. Several aspects of fruit ripening are to some extent controlled by vine water status. Properly timed water stress increases the color of red winegrape juice, the concentration of phenolics (tannins), and the concentration of amino acids in juice of red and white varieties. As long as the water stress is moderate, these changes occur without significant effects on sugar accumulation and titratable acidity. The timing of water stress is important. For color and phenolics, stress early in the season (before veraison) is more important. However, early season stress also leads to significant decreases in the concentration of malate (increasing the tartrate:malate ratio) which may be perceived as positive or negative, and leads to inhibited yields in the following season. Water stress after veraison (a common practice), is more important than early stress in increasing the concentration of amino acids in the harvested juice and also decreases the relative amount of proline in the total amino acids. This is important because proline is largely unavailable for yeast during fermentation. Postveraison stress is less effective in increasing color, phenolics, and the tartratermalate ratio. If late stress is severe enough, delayed ripening and inhibited yield in the following season occur. These differences in fruit composition lead to significant differences in the appearance, aroma, and taste of wines. The results of sensory analyses indicates that all stresses are not equal. That is, the appearance, aroma, and taste of a wine made from vines that experienced and early stress are different from those attributes of a wine made from vines that experienced water stress only after veraison. We are now testing whether these changes in fruitfulness, fruit composition, and wine sensory attributes are due to water stress directly or are due to the effects of water stress on the canopy microclimate. If the latter is true, water stress may not be necessary to obtain these differences. Early season water deficits increased light and air temperature in cluster zone throughout much of the season. Postveraison water deficits can also cause an increase in light in the cluster zone, apparently due to leaf abscission which we intend to quantify in 1992. Another approach was to include treatments that counteracted the effects of the irrigation treatments on microclimate. In some control vines, leaves were removed to open the canopy and make conditions similar to those experienced under the Early deficit treatment. Likewise, in some Early deficit vines clusters were bagged with shade cloth to decrease light penetration. The results suggest that changes in fruit growth and composition that occur in response to water stress are unlikely to be due to changes in the canopy; rather fruit responses appear to be due to changes in the physiology of the berry caused by water stress conditions. However, these treatments, partial defoliation of control vines to create “Early deficit-like” canopies and shading of Early deficit clusters were only partially successful in accurately recreating the alternative cluster environments. The plan for 1992 includes modifications in these treatments to more accurately reproduce their alternative cluster environment goals and sensory analysis of Pinot noir and Cabernet Sauvignon wines from different water stress treatments.

Trellises for Wine Grape Canopy Management in the San Joaquin Valley

A wine grape trellis trial was designed and planted in 1986 at the U.C. Kearney Agricultural’ Center in the San Joaquin Valley. The purpose was to determine the most suitable trellis system for optimum fruit production and composition in cultivars of major importance to the area; ease and economics of vine management and mechanization were also considerations. Two cultivars, French Colombard and Barbera, were tested on 8 trellis designs suited to mechanization over 3 years, 1989-91. Data collection involved measurements of vine growth and light environment and fruit characteristics and composition; wine making, must and wine composition, and wine sensory analysis were also performed. Contrast analysis was conducted on major comparisons of vine training and trellis configuration for individual years and all 3 years (overall effects). The addition of one foliage support wire above bilateral cordons (11″ distance) increased pruning brush weights; vine yield was also increased through increased berry and cluster weights and with little or no effect on fruit composition in both cultivars. Similar effects were also obtained by increasing the bilateral cordon height by 11″ in both cultivars and with some advanced fruit maturation in Barbera.

Vineyard canopy management practices for improving grapevine

The main conclusions from a four-year study of trellising, row spacing and pruning level of Cabernet Sauvignon at the Oakville Experimental Vineyard are as follows: 1. Reducing row spacing from 12 feet to 8 feet increased crop yield by 35{aed9a53339cdfc54d53cc0c4af03c96668ab007d9c364a7466e3349a91bf0a23} or 2.8 tons/acre with little or no significant difference in fruit composition. 2. At each of the three row spacings, quadrilateral cordon (QC) trellised vines produced approximately two tons/acre higher yield than bilateral cordon (BC) trellised vines averaged over a period of four years. 3. At the same level of “Brix at harvest, QC fruit had lower pH and higher levels of anthocyanins than BC fruit. 4. The higher level of anthocyanins in QC fruits than BC fruits was correlated to greater amount of photosynthetic active radiation in the fruiting region of the former treatment. 5. Increasing the pruning level from 24 to 60 buds per vine increased crop yield from 6.6 tons/acre to 11.0 tons/acre. 6. With increase in the number of buds per vine from 36 to 60 there was an average of 7 to 10 days delay in ripening. 7. At harvest, fruits from vines pruned to 48 and 60 buds/vine had lower pH, TA, malic acid and K and higher anthocyanin than vines pruned to 24 and 36 buds per vine. 8. Dividing the canopy, reducing distance between rows, and increasing the number of buds per vine all reduced shoot length, shoot weight, pruning weight per vine, and primary and lateral leaf area per shoot and increased the cropping efficiency. 9. The canopy density of QC trellised vines was significantly less than BC trellised vines. 10. Sensory analysis showed that BC wines could be distinguished from QC wines. 11. Sensory analysis could not distinguish between low crop wines (24 buds/vine) and high crop wines (60 buds/vine).

Water Conservation in Wine Grape Production

An infrared thermometer (IRT) was used to schedule irrigation in five vineyards. Chardonnay vines in Madera and Santa Maria, CA; Chenin Blanc vines in Madera, CA; and Cabernet Sauvignon vines in Madera and Paso Robles, CA were used in this project. Water was applied to drip irrigated vines only when IRT measurements indicated a certain level of water stress. If vines were below that stress level, water was withheld until stress increased to the selected level. Treatments were imposed from veraison to harvest at the Madera and Santa Maria locations; and from berry set to harvest at the Paso Robles location. Water use for irrigation was reduced by up to 3 0{aed9a53339cdfc54d53cc0c4af03c96668ab007d9c364a7466e3349a91bf0a23} in this study. The amount of water saved depended on environmental conditions and the irrigation scheduling practices of the grower-cooperator. Irrigation scheduling treatments had no significant effect on vine yield or dormant pruning weight. Fruit composition displayed only a small response to the treatment. In general, {aed9a53339cdfc54d53cc0c4af03c96668ab007d9c364a7466e3349a91bf0a23} soluble solids of fruit were increased by increasing water stress. The effect of treatment on titratable acidity and pH was not consistent. These results are preliminary and several more years of data collection are required before equilibrium results can be obtained. Commercially available microsprayers were tested in the Center for Irrigation Technology Sprinkler Testing Laboratory on the CSU, Fresno campus. All microsprayers tested were not suitable for targeted frost protection of vines. Prototype microsprayers from two manufacturers were also evaluated. The Wade Manufacturing Pulsator was identified as being capable of providing adequate targeted frost protection with a flow rate of approximately 11 gpm/acre. Thus, the commercial application of this technology would substantially reduce water use for frost protection. Additional testing is needed to evaluate the Pulsator microsprayer under field conditions using differential application rates.

WATER REQUIREMENTS DURING AND AFTER VINEYARD ESTABLISHMENT FOR CHARDONNAY GRAPEVINES GROWN IN THE CARNEROS DISTRICT

A study was conducted to determine the water use or vineyard evapotranspiration (ET) of Chardonnay grapevines during vineyard establishment. ET is the combined loss of water by evaporation from the soil and transpiration by the vine. The experimental vineyard was 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 were differences in water use between them. Vineyard 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 (also called a hydroprobe or soil moisture gauge). Access tubes, needed to measure soil water content, were placed at eight sites throughout the vineyard (four sites per rootstock). At each site six access tubes were placed such that the soil water content in one quarter of the vine’s root volume could be quantified down to a depth of 3 m (10 ft) . The tubes were placed equidistant from one another: two tubes in the vine row, two tubes midway between rows and two tubes midway between the four tubes mentioned previously. The tubes also extended midway between vines within a row. The vineyard was planted with the rootstocks in June of 1990. In the Fall, the rootstocks were chip budded with Chardonnay scion buds. Starting the first week in July, soil water content (SWC) was measured at all eight sites (four sites per rootstock) weekly. Soil water content the first year declined slightly from the first measurement date throughout the remainder of the season. This indicated that the vineyard was irrigated at slightly less than vineyard ET during that time. Approximately 3 0{aed9a53339cdfc54d53cc0c4af03c96668ab007d9c364a7466e3349a91bf0a23} of the water used by the vines was supplied by the soil, with the rest being provided by the irrigation water. The total amount of water used by the vines (averaged across both rootstocks) from July until the end of October was approximately 117 mm (4.6 inches) of water. This was equivalent to 380 liters (100 gallons) of water per vine during that time. Potential evapotranspiration (ETJ , determined at the CIMIS (California Irrigation Management Information System) weather station at Oakville was 575 mm (22.6 inches) of water from July to the end of October. Potential ET is the calculated water use of a short, green, well irrigated reference crop (usually a grass) . The use of water by the grass is used for comparison with the use of water by other crops. ET? is needed to develop crop coefficients. In 1991, SWC increased during the first six weeks of the season indicating that the vines were being over-irrigated. After that, SWC decreased for the next six weeks and then remained constant from then until the end of October. These results indicated that the vineyard was irrigated at close to vineyard ET during the major portion of the growing season. Again, approximately 3 0{aed9a53339cdfc54d53cc0c4af03c96668ab007d9c364a7466e3349a91bf0a23} of the water used by the vines in this vineyard was supplied by the soil. The total amount of water used by the vines (average of the two rootstocks) from April until the end of October was 175 mm (6.9 inches) of water. This was equivalent to 563 liters (150 gallons) of water per vine. ET0 measured at the Oakville CIMIS weather station was 810 mm (31.9 inches). Leaf water potential was measured several times during the 1991 growing on the Chardonnay scions within the vineyard. Leaf water potential is a measure of the water status of a plant. It previously has been demonstrated that leaf water potentials less negative than -1.0 MPa indicate that the vine is not under water stress. In this study, leaf water potential values for vines on both rootstocks were less negative than -0.9 MPa, indicating that during the growing season the vines were probably not under stress. It also indicates that the vines had been irrigated at amounts close to what the vines actually used. The water used by the vines in this vineyard was less than half that used by grapevines growing in the San Joaquin Valley during similar periods of vineyard establishment. For example, vineyard ET was 300 mm (11.8 inches) and 400 mm (15.7 inches) of water the first and second years, respectively, for a Thompson Seedless vineyard compared to 117 (4.6 inches) and 175 (6.9 inches) for this vineyard during the same years of vineyard establishment. This would be expected as evaporative demand is much greater in the San Joaquin Valley compared to the Carneros district. In addition, this Chardonnay vineyard was not planted until the last week in June compared to an April 10 planting date for the Thompson vineyard (therefore, a shorter time period for taking measurements in the first year of vineyard establishment at the Carneros site). Another reason for the lowered water use reported here was that vine growth was much less for the Chardonnay vines compared to the Thompson Seedless vines grown near Fresno. The data contained in this report is the first the authors are aware of in which vine water use was quantified for vines grown in a cool climate during vineyard establishment. This study will continue for another four years, including years in which vines will be in full production. Lastly, crop coefficients will be calculated for each year of the study and then be used for future irrigation management practices.