Grape-based agriculture in the Western SARE region has been a major industry historically with rapid expansion occurring in recent decades in the Pacific Northwest. However, water for crop irrigation now faces potential limits owing to multiple competing demands from the public as well as from changing climatic patterns. Agriculturalists are currently being forced to make essential decisions ranging from crop selection to management strategies in order to maintain sustainable operations. Owing to moisture losses associated with surface evaporation and weed growth under conventional surface irrigation methods, development of more highly efficient irrigation methods are necessary for producers to meet this resource use challenge. Working in close collaboration with vineyard owners and managers in southcentral Washington, our research group recently introduced a new subsurface micro-irrigation strategy which uses hard tubes placed vertically into soil to deliver water directly into the lower root zone of certain perennial crops such as grapes. During the 2015 growing season, one of the hottest and driest on record, we were able to produce 70 percent of commercial production using direct root-zone irrigation while conserving 85 percent of the water applied by surface drip irrigation to achieve full commercial production. We anticipate that this study will clarify the advantages of our new irrigation method for growers when coping with water scarcity in the western region of the U.S., and also gain a better understanding of growth capacities of grapevines under water stress. These results will be translated to growers through an integrated applied research and educational program with primary objectives focused on: 1) advancing the understanding of the role of water in allocation of carbohydrates within the grapevine; and 2) extension education programming directed by a logic model developed to guide project activities. Our proposed activity plan is based on stakeholder input and involvement, sound experimental design involving statistical principles, and an educational programming model containing proven methods. We will utilize on-farm demonstration, formal educational programs containing learning assessment, and surveys to track rate of adoption by growers and determination of resulting economic impact to the grape-based industry in the western U.S.
Overall goal: Achieve comprehensive understanding of subsurface micro-irrigation impacts on grapevine growth and wine quality by determining minimal amounts of water required to achieve acceptable fruit quality. Growers will be directly engaged with this project through planned program activities to translate research-based findings to provide efficient and sustainable irrigation methods for vineyard managers to utilize during periods of limited water availability.
Objective 1: Evaluate efficiency of our subsurface micro-irrigation strategy on water conservation
- Sub-objective 1: Calculate water saved without diminishing fruit quality
- Sub-objective 2: Compare differences in water use efficiency between subsurface micro-irrigation and surface drip irrigation
- Sub-objective 3: Determine combinations of water delivery amount and irrigation depth yielding highest water use efficiency
Objective 2: Measure the impact of our new subsurface micro-irrigation strategy on grapevine growth and fruit quality
- Sub-objective 1: Assess role of subsurface micro-irrigation strategy in partitioning carbohydrates within the grapevine
- Sub-objective 2: Quantify subsurface micro-irrigation effects on root distribution and abscisic acid (ABA) exudation
- Sub-objective 3: Analyze vital nutrient content in grapes
Objective 3: Educate vineyard producers and engage community members on irrigation water conservation and wine grape quality improvement
- Sub-objective 1: Conduct extension workshops or field days to educate producers about improving wine grape quality by using less irrigation water
- Sub-objective 2: Develop educational materials for vineyard managers and growers to conserve irrigation water and improve water use efficiency
1) Field research
Subsurface micro-irrigation system was installed in a commercial block of Cabernet Sauvignon wine grapes located on Kiona Vineyards in the Red Mountain AVA near Benton City, WA in early 2015, and duplicated in another vineyard planted to Chardonnay wine grapes near Prosser in the Yakima Valley AVA in 2016 (Fig. 1). Experiments were established according to a randomized complete block design with 3 blocks, and each block has 5 replicates of main treatment effects. PVC tubes are used to vertically deliver water to precise depths (30, 60, and 90 cm) in the lower root zone, and electronic irrigation controllers are employed to schedule water delivery at rates of 60, 30, and 15 percent of the commercial rates used for surface drip irrigation. All fertilizers and herbicides are applied commercially as uniformly across the vineyard as possible.
Grapevines are fully irrigated right after bud break till the time before fruit set to replenish soil water content after winter, then we switch it to deficit irrigation by implementing our treatments (3 irrigation depths * 3 irrigation rate = 9 treatments) from fruit set to harvest to control shoot growth and fruit quality. Commercial irrigation timing and rates are controlled by each vineyard manager depending on soil moisture content and their production goals.
Each year, grapes are harvested by hands (Fig. 2), and are weighed by digital scale for yield data. Besides, grape samples are picked from each treatment plot for quality analyses. Leaf samples at each key stage (fruit set, veraison, and harvest) are collected from each treatment plot for abscisic acid (ABA) analysis. At harvest, leaves, shoots, and roots are collected for carbon partition analysis. Grapevines are pruned in winter to measure shoot biomass. Moreover, the minirhizotron system (CI-600 in-situ root imager, CID Bio-science, Inc., WA), which is designed to slide down inside a transparent tube and to take root pictures belowground, is used for observations of root growth and distribution (Fig. 3). Leaf water potential is measured by pressure chamber at midday. Weather variables, such as air temperature, relative humidity, and rainfall, are recorded by WSU weather station nearby.
2) Greenhouse research
A supplementary research was initiated in greenhouse in April 2016 to compare the biomass partitioning and root growth of young vines under different irrigation rates and depths (Fig. 4). Daily temperature and illumination periods are automatically controlled at 75°F/16h at daytime and 55°F/8h at night. Experimental seedlings of Cabernet Sauvignon are donated by Inland Desert Nursery, Inc. (Benton City, WA). In 2016, We randomly selected 24 seedlings in similar weight and height, and consecutively planted them in each of pots with 30 cm wide and 120 cm deep. 24 minirhizotron tubes in 142 cm long were inserted into pots before filling topsoil up for root observation, and root images are taken periodically. We set 4 watering levels (full, high, medium, and low), and water vines at approximately weekly intervals. At first, we fully watered all seedlings for 4 weeks to break their dormancy and help them adapt to the greenhouse condition, and then started our treatments in fifth week.
Another pot experiment was finished in September 2016, which was focused on how grapevines allocate biomass to roots, shoots, and leaves under 3 different watering levels (high, Medium, and low). It was a randomized complete block design with 4 blocks, and each block had 5 duplicates of vines under each treatment. We harvested 1 seedling under each treatment replicate from each block every month from May to September to observe dynamics of biomass allocation.
We have conducted field experiments in Kiona vineyard (Cabernet Sauvignon) for three years since 2015, and two years in Hogue Ranches vineyard (Chardonnay) since 2016, which were mainly focused on grape production and water conservation under subsurface micro-irrigation. During the growing season in 2015, one of the hottest and driest on record, we could produce 70% of commercial production of Cabernet Sauvignon using subsurface micro-irrigation while using only 15% of the water applied by surface drip irrigation to achieve full commercial production. Moreover, fruit production was only 10% less that of commercial rates with 60% the water applied as surface drip with full commercial rates. Similar results were received from plots of Chardonnay in 2016. Surprisingly, we didn’t see any improvement of water use efficiency on grape yield of Cabernet Sauvignon under 60% irrigation rate in 2016, however, grape qualities increased with the decrease of water use. We had plenty of precipitation early in 2017, combined with a short growing season, and no significant difference of treatments were found from our study. Based on visual observation and partial physiological data collected, we hypothesize that length of growing season and precipitation heavily influence irrigation efficiency in a dry-land area.
During the 2016 growing season, we also conducted both greenhouse and field experiments to observe the root growth under deficit irrigation. Root biomass significantly decreased with the water stress increased (P < 0.05). Vines receiving the full watering rate accumulated biomass faster than vines in deficient watering rates (P < 0.05) during the early and middle growing seasons. During the late growing season, biomass accumulation for vines in median and full watering rates became similar, but both were still significantly higher than vines in low watering rate (P < 0.05). The ratio of below- to above-ground biomass for vines in median watering rate was significantly higher than the ratios for vines in full and low watering rates (P < 0.05), which means vines might allocate more carbon resource into root growth under appropriate water deficiency. Additionally, roots were found to develop deeper into the soil profile under water stress, which could be considered a survival strategy that helps plants access water during extended drought in deeper soils (Fig. 5).
Educational & Outreach Activities
Right after we received this funding support, we had an on-farm demonstration combined with Washington viticulture field day which was held by WSU Viticulture and Enology Program (August 12, 2016). A presentation about deep irrigation was given by our project team, which discussed research on subsurface irrigation strategy and plant response. Besides, we showed our irrigation equipment (electronic controllers, water delivery tubes, etc.) to growers and students, and demonstrated how we regulate this subsurface micro-irrigation system in vineyard (Fig. 6).
1) WAVE Minute: Irrigation Developments. 2017. Washington Ag Network. August 3: http://www.washingtonagnetwork.com/2017/08/03/wave-minute-irrigation-developments/. This radio news recorded by Glenn Vaagen discusses our latest irrigation technology and research taking place at WSU.
2) Study pushes limits of deficit irrigation. 2017. Good Fruit Grower. July 24: http://www.goodfruit.com/study-pushes-limits-of-deficit-irrigation-trials/. This article written by Kate Prengaman describes our research in Red Mountain AVA.
3) Deeper irrigation method showing promise for vineyards. 2016. Growing Produce. August 23: http://www.growingproduce.com/fruits/grapes/deeper-irrigation-method-showing-promise-for-vineyards/. This article written by Brian Wallheimer shows promise of our irrigation system in vineyards and interests from growers.
Talks and presentations:
1) Xiaochi Ma, Pete Jacoby, Karen Sanguinet. 2017. Influences of direct root-zone deficit irrigation on wine grape production, grapevine growth, and root distribution in Pacific Northwest. American Society of Agronomy, Crop Science Society of America, and Soil Science Society of America (ASA, CSSA, SSSA) 2017 Annual Meeting. October 22-25. Tampa, FL. (1st place award – graduate presentation category).
2) Xiaochi Ma, Pete Jacoby, Alexis Torp, Gillian Hawkins, Lindsey Mongan. 2017. Effects of root-zone deficit irrigation on crop growth, fruit yield, and agroecosystem stability: using the wine grapevine Cabernet Sauvignon as a model. Ecological Society of America 102nd Annual Meeting. August 6-11. Portland, OR. https://eco.confex.com/eco/2017/webprogram/Paper66329.html.
3) Xiaochi Ma, Jeremy Thompson, Pete Jacoby. 2017. A strategy to enhance water conservation and sustain grape production in Pacific Northwest. Center for Precision & Automated Agricultural System (CPAAS) Agricultural Technology Day. July 31. Prosser, WA. 2017-CPAAS-Poster-Xiaochi-Ma
We gave a poster presentation, and had a good networking with local growers, agricultural industry professionals, crop consultants and researchers during this event, which was hosted by WSU CAHNRS’s Center for Precision & Automated Agricultural Systems (Fig. 7).
4) Pete Jacoby, Xiaochi Ma, Jeremy Thompson. 2017. Maintaining vineyard production with season-long deficit irrigation. 68th American Society of Enology and Viticulture National Meeting. June 26-29. Bellevue, WA.
5) A talk given by Pete Jacoby: Novel irrigation delivery system. 2017. Washington Advancements in viticulture & Enology (WAVE), Washington Wine Industry’s Research Program, International Masters of Wine WA/OR Tour. May 2. Richland, WA.
Dr. Pete Jacoby gave this talk about our advance irrigation system and research conducted in vineyards to more than 50 Masters of Wine (MW), the people from different countries who have demonstrated thorough knowledge of all aspects of wine and ability to communicate clearly (Fig. 8).
6) Pete Jacoby, Xiaochi Ma, Jeremy Thompson. 2016. Effects of root-zone micro-irrigation on Cabernet Sauvignon. Proceedings: Technical Education Conference on Use of Micro-irrigation in Agricultural Cropping Systems, Irrigation Show & Education Conference. December 5-9. Las Vegas, NV.
7) Xiaochi Ma, Pete Jacoby, Jeremy Thompson. 2016. Assessing impacts of direct root-zone irrigation on grapevine physiology. American Society of Agronomy, Crop Science Society of America, and Soil Science Society of America (ASA, CSSA, SSSA) 2016 Annual Meeting. November 7-11. Phoenix, AZ. (3rd place award – graduate poster category). https://scisoc.confex.com/crops/2016am/webprogram/Paper100398.html.
Educational tool – Web page:
We built a stand-alone web page for this project in early 2017 that is linked with Jacoby’s laboratory page at Washington State University (https://labs.wsu.edu/jacoby/). This page currently provides general information about our project and announcements we have for our education & outreach events. We also show our latest press releases and scientific publications that are related with this project on our website.
Upcoming publications and presentations in 2018:
We will write one peer-reviewed paper, and at least two extension articles based on this project. Plus, we will give at least four presentations to enhance the recognition of this project.
Project outcomes will be shown on our final report after we receive complete results from our research, and from our education & outreach activities.