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50 WINES&VINES June 2017 GRAPEGROWING PRACTICAL WINERY & VINEYARD Deficit irrigation regimes A deficit-irrigation study was conducted at Cold Creek Vine- yard, a property owned by Ste. Michelle Wine Estates that was planted in 1981 in the Columbia Valley appellation in southeast- ern Washington state. The trial was conducted in 2011, 2012 and 2013 on own-rooted Caber- net Sauvignon grapevines (clone FPS 08). Cold Creek Vineyard was irri- gated using drip irrigation with pressure-compensating, 1-gallon- per-hour emitters spaced 3.5 feet apart. Vine spacing was 6.8 feet between vines with 9.8-foot-wide tractor rows. Vines were trained to bilateral cordons at 3.5 feet aboveground and spur-pruned in winter to 67 nodes. Shoots were loosely positioned between two foliage wires, and the trial re- ceived standard applications of fertilizers, herbicides and other pest- and soil-management prac- tices as other blocks in the vine- yard. Because the vineyard did not receive enough precipitation in winter months to replenish the soil-moisture profile, the root zone was irrigated to near field capacity prior to bud break. Weather data collected daily from an on-site weather station owned by Ste. Michelle Wine Es- tates is summarized in the table "Summary of Weather Condi- tions." Cumulative growing de- gree-days were calculated from daily maximum and minimum temperatures, with a base tem- perature of 50° F from April 1 to Oct. 31. Four temperature thresh- olds were counted separately to identify the number of hot and very hot days (temperatures above 86° F and greater than 95° F) during pre-véraison and ripening, and two temperature thresholds were used to identify the number of cool and cold days (less than 59° F and less than 50° F) in the spring and fall. Four irrigation regimens were applied in four replicated blocks to replace a range of crop evapotrans- piration (ETc) fractions from fruit set to harvest. Evapotranspiration (ET) is the sum of evaporation of water from the soil and plant tran- spiration and uses a reference crop surface such as grass, without any water stress, multiplied by a grape- vine-specific and seasonally vari- able crop coefficient to calculate the crop's water use. 8 The trial was designed to vary the timing and extent of water deficit from no water stress to relatively severe stress. The same vineyard was part of previous deficit-irrigation research con- ducted in the three years leading up to the present trial. 9 The overall goal of this study was to investigate the impact on fruit and wine composition from more widely contrasted irrigation regimes than were previously studied. 10 The study measured vine growth and yield compo- nents, plant water status and gas exchange and canopy microcli- mate. Although experimental wines were made by co-investiga- tor Dr. Jim Harbertson's team, the effects on fruit and wine composi- tion are not covered here but will be contained in other reports. Irrigation regimes were imple- m e n t e d w h e n s h o o t g r o w t h stopped, which typically occurred soon after fruit set. The four irri- gation treatments were: • 100% ETc (ET 100 ) • 70% ETc (ET 70 ) • 25% ETc (ET 25 ) • 25% ETc before véraison, 100% ETc thereafter (ET25/100) All treatments were fully irri- gated after harvest in preparation for winter. Although there was yearly variation in the three grow- ing season temperatures, the ef- fects from irrigation treatments were consistent between years. Deficit irrigation treatments did not enhance water-use effi- ciency: Lower seasonal irrigation water supply was also associated with lower yield, but deficit irriga- tion did reduce water use. The average amounts of irrigation water supplied over three years varied from 16.0 inches (1.3 acre- feet) in the ET 100 treatment; 12.6 inches (1.05 acre-feet) in the ET 70 vines; 11.4 inches (0.95 acre-feet) in the ET25/100, and 6.8 inches (0.5 acre-feet) in the ET 25 . On average, deficit irrigation reduced the amount of water supplied by 22% in the ET 70 , 31% in the ET25/100, and 56% in ET 25 . Vine vigor Vines in this trial exhibited most of their shoot growth before fruit set. Though primary shoots in all treatments stopped growing be- fore véraison, lateral shoots in the ET 100 and ET 70 vines continued to grow through harvest. Effects on vine vigor, size and density of canopy from irrigation were con- sistent across the three years. SUMMARY OF WEATHER CONDITIONS Year GDD (°F) a Seasonal temperatures (d) b Precipitation (in) >86ºF PV/RP >95ºF PV/RP <59ºF S/F <50ºF S/F Annual Seasonal c 2011 2,959 32/16 2/2 20/9 1/1 3.6 2.1 2012 3,305 50/4 15/0 7/9 1/4 4.0 1.8 2013 3,528 55/19 16/1 10/6 0/0 1.9 1.5 1995- 2013 3,245 53 13 10/9 0/2 4.7 2.2 Data were collected by an on-site weather station located less than 400 meters from the experimental vineyard block in southeastern Washington. a Cumulative growing degree-days (>50°F) from April 1 to Oct. 31. b Number of days from April 1 to Oct. 31 with maximum temperatures above or below four threshold temperatures. (PV: pre-véraison/RP: ripening; S: spring/F: fall). c Cumulative rainfall from April 1 to Oct. 31. SHOOT VIGOR AND VINE SIZE Shoot length a (inches) Lateral leaves (per shoot) Pruning weight (ounces/foot) Weak canes c (%) ET 25 27 b b 10 b 2.2 c 33 a ET 25/100 35 a 16 b 3.9 b 25 b ET 70 36 a 23 a 4.6 ab 27 ab ET 100 39 a 22 a 5.6 a 22 b 2011 41 a 23 a 3.6 b n.d. 2012 31 b 15 b 3.8 b 30 a 2013 32 b 15 b 4.9 a 23 b Cabernet Sauvignon grapevines irrigated at various fractions of crop evapo- transpiration (denoted by subscripts of ETc) from fruit set to harvest over three years; ET 25/100 refers to 25% ETc before véraison and 100% ETc thereafter. a Length of primary shoots at harvest. b Means followed by different letters differ significantly at p < 0.05 by Duncan's new multiple range test. c Proportion of canes with less than five nodes (not determined in 2011). YIELD AND YIELD COMPONENTS Yield (tons/acre) Berries/ cluster Berry weight (g) Yield: pruning weight (pounds) ET 25 2.1 b a 69 c 0.84 c 7.3 a ET 25/100 3.8 a 89 a 0.95 b 8.2 a ET 70 3.9 a 76 bc 1.08 a 7.1 a ET 100 4.4 a 80 ab 1.06 a 6.9 a 2011 2.5 b 70 c 1.18 a 6.6 a 2012 3.8 a 79 b 0.84 c 8.6 a 2013 4.3 a 88 a 0.93 b 7.0 a Cabernet Sauvignon grapevines irrigated at various fractions of crop evapo- transpiration (denoted by subscripts of ETc) from fruit set to harvest over three years; ET 25/100 refers to 25% ETc before véraison and 100% ETc thereafter. a Means followed by different letters differ significantly at p < 0.05 by Duncan's new multiple range test.