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

A study is being 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 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 were differences in water use between the two. The rootstocks were planted in June of 1990 and Fall chip budded with the Chardonnay scion. Vineyard water use was determined by measuring soil water depletion and monitoring the addition of water via irrigation or measured rainfall. 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 places such that the soil water content in one quarter of an individual vine’s root volume could be quantified down to a depth of 3 m (approximately 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 v\Lnes within a row. The year 1992 represented the third growing season for this vineyard. Soil water content decreased rapidly early on in the growing season until the end of May. After this time soil water content remained constant until the end of October. The depth of water extraction from the soil extended down 1.3 m (4.25 ft). The constancy of the soil’s water content from June until October indicated that the water applied via irrigation equaled the amount of water used by the vineyard. The average seasonal water use of both rootstocks was 236 mm (9.3 inches) of water. This is equivalent to approximately 750 1 (200 gallons) of water per vine. The amount of water used by the vines supplied from the soil resevoir was 42{aed9a53339cdfc54d53cc0c4af03c96668ab007d9c364a7466e3349a91bf0a23} of the total amount used. Midday leaf water potentials were measured every two weeks during the season. Leaf water potential is a measure of a vine’s water status and would give an indication as to whether the vine experienced stress at any time. Of the eleven times measurements were taken, leaf water potential readings on nine dates indicated that the vines were not under stress (values were less negative than – 0.8 MPa or -8 bars) . However, on two of the dates leaf water potentials became more negative than -1.0 MPa. Values more negative than -1.0 MPa are associated with vine water stress in mature vines. It should be pointed out that on both of those dates ambient temperatures were greater than 32°C (90°F) and relative humidities were quite low. This information would indicate that irrigation amounts should have been increased during those periods when evaporative demand was greater than normal. One of the primary objectives of this study is to determine crop coefficients for vines grown in a cool climate during vineyard establishment. The crop coefficient for this vineyard started out at 0.5 and decreased thereafter until day of year 220 (approximately the first week in August) when the crop coefficient reached a minimum of 0.2. Subsequent to this date the crop coefficient increased and reached a maximum of 0.4 at the end of the growing season. The relatively high crop coefficient early in the season could have been due to the percolation of water below the depth of the access tubes (which would have been measured as vineyard water use) and the fact that a natural cover crop had been established during the winter months. The cover crop would have used a considerable amount of water until the vine rows started drying out. The increase in the crop coefficient from August until the end of the growing season was due to the continued growth of the vines up to November. An increase in the crop coefficient up to the end of the season has previously been reported for vines grown in the San Joaquin Valley during the second year of vineyard establishment.

Water Conservation in Wine Grape Production

An infrared thermometer (IRT) was used to schedule irrigation and impose selected levels of stress in two vineyards during the 1992 season. Cabernet Sauvignon vines in Paso Robles, CA and French Colombard vines in Ripperdan, 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 berry set to harvest. Water use was reduced during the berry set to harvest period by up to 50.3 and 39.0{aed9a53339cdfc54d53cc0c4af03c96668ab007d9c364a7466e3349a91bf0a23}, respectively for Cabernet Sauvignon and French Colombard vines. Treatments which exposed vines to moderate levels of stress for the entire berry set to harvest period produced the greatest reductions in water use. Irrigation scheduling treatments had no significant effect on yield or dormant pruning weight of Cabernet Sauvignon vines. However, growth and yield of French Colombard vines were significantly reduced by all programmed water stress treatments. Fruit maturity was generally advanced by increasing water stress but differences were often not statistically significant. These results are preliminary and several more years of data collection are required before equilibrium results are obtained. The Wade Manufacturing Pulsator microsprayer was subjected to further developmental testing in the Center for Irrigation Technology sprinkler testing laboratory to refine its application pattern. A commercial plot was established in a Chardonnay vineyard near Los Alamos, CA and field testing of the Pulsator occurred this spring. Analysis of data is not complete but it appears that the Pulsator microsprayer was as effective as overhead sprinklers for frost protection.

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.

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.