Location: Water Management Research2012 Annual Report
1a. Objectives (from AD-416):
Determine the effects and limits of deficit irrigation strategies on the yield and quality of wine and juice grape.
1b. Approach (from AD-416):
The research will be a combination of field studies on cooperating farms, laboratory studies at Washington State University.
3. Progress Report:
This project supports objective 1 of the parent project. This research is being conducted in support of the NIFA-SCRI project “Developing Sustainable Vineyard Water Management with Limited and Impaired Water Supplies”. The first deliverable is “Develop and recommend sustainable water management strategies for wine, table, raisin, and juice grape production using limited and impaired water supplies”. This project is located in Prosser, Washington and is evaluating the water management strategies for juice (Concord) and wine (Cabernet Sauvignon) grown in Washington State in support of the first deliverable. The wine grape study complements research on Cabernet Sauvignon being grown on the coast of California. Prior to the 2011 field season, we concentrated on development and implementation of project parameters specific to our site location. As per project guidelines, we worked with the owner of Airfield Ranches, to select a Concord and Cabernet Sauvignon block suitable for this trial. The treatment parameters for both the Concord and Cabernet Sauvignon grapes were determined based on guidelines set forth in the original proposal with consideration given for local climatic constraints, current irrigation infrastructure, and grower concern. The four treatments for the Concord block were determined to be; 1) Control – current vineyard practice, 2) 100% evapotranspiration (ET), 3) 85% ET and, 4) 70% ET. These irrigation deficits would be induced from bloom to verasion. Prior to this treatment period and post treatment irrigation would be set based on the grower’s current practices. For the Cabernet Sauvignon the treatments are as follows; 1) Control – current vineyard practice, 2) 1/3 increase in irrigation all season, 3) 1/3 increase in irrigation until fruit set, stop, then a 1/3 increase again at verasion, and 4) a 1/3 increase at 50% verasion. Within each vineyard, there were four replicate blocks containing each treatment, one through four, in a random distribution. This was done to ensure any differences in soil and microclimate characteristics were minimized. Plots were outfitted with additional irrigation piping as needed in both the Concord and Cabernet Sauvignon vineyards to meet treatment water requirements. To monitor soil moisture, neutron probe access tubes were installed between the 2nd and 8th data vines in each plot. Additionally, four watermark soil moisture sensors were placed in each vineyard with one set per treatment in a single replicate. The watermark sensors were installed to provide consistent measurement techniques between all grapes in this study both in Washington and California. At the beginning of the season, we took three measurements of the shaded area under the canopy (Paso panel measurements) per treatment to characterize the grapevine canopies of both the Cabernet and the Concord, resulting in a total of twelve samples per treatment. Because of intensive management in the Cabernet vineyard (canopy positioned, shoot thinned, leaf thinned, hedged), there were stable readings with the Paso panels throughout the summer. However, the Concord canopy proved to be much more consistent with typical management practices for juice grape in central Washington. Thus, the sample size was increased from three measurements per treatment to nine samples per treatment. This stabilized the average Paso panel reading and increased the accuracy of the crop coefficient calculations. During the 2011 growing season, soil moisture monitoring was conducted on a weekly schedule. Since these measurements were not in concert with these irrigation events, we altered the schedule for timing soil moisture monitoring to occur within 28 hours after an irrigation event. Collecting data in the new schedule has allowed for a clearer visualization of the differences the treatments are making in the soil moisture. The irrigation treatments have an effect on the soil moisture in the top 30 inches of soil. The weather also played a major role in the delayed development of Yakima Valley grapevines in 2011 due to an abnormally cool spring. As a result, the phenological stages of grape development (bloom, fruit-set, verasion) were later than the historical average for the region. Between the two years of this study, 2012 is closer to the historical average of 520 growing degree days (GDD) with 456 accumulated GDD to date, while 2011 clearly lagged behind with only 292 GDD accumulated to date. In addition to changes in methodology described above, two additional measurements were included to characterize the soil moisture in relationship to the treatments over time. To characterize the distribution of soil moisture of the different treatments adjacent to both a drip emitter and a vine, soil samples are being collected in a radial pattern. Centered under a drip emitter located between two data vines, soils were sampled in 25 locations in the cardinal directions (N to S, E to W, NE to SE and NW to SW) at three widths (50, 100 and 150cm from the emitter), and four depths (20, 40, 60, and 80cm). This will provide a three dimensional picture of soil moisture within the vineyard. Sample times occurred at 3-4 leaf stage, pre-verasion, and third pre-final irrigation. These times coincide with times most likely to illustrate treatment differences and persistence. Additionally, depth of the neutron probe measurements was increased from 3 feet to 5 feet to improve understanding of soil moisture in response to treatment throughout the entire soil profile.