Quantifying the Influence of Irrigation and Meteorology on Water Use Efficiency at a Vineyard in Washington

Washington State has taken its place as the second largest grape producer in the United States. With the warming of the climate and the future growth of population, it may be possible that water will become a much scarcer resource. This presents a problem for the growers and their ability to make decisions on how to use their water, versus the quality of grapes produced. To help Washington grape growers make informed decisions in regards to irrigation strategies, Washington State University is running a pilot study to better understand Water Use Efficiency (WUE) at Ciel du Cheval vineyard on the Alcora Estate in Benton City, WA. In this pilot study, an eddy covariance tower was installed at a vineyard, watered by a drip irrigation system, to measure the net ecosystem exchange (NEE) and evapotranspiration (ET) of the grape vines, as well as other meteorological factors. Water use efficiency has been defined as the ratio between NEE and ET, and in this study, WUE will help the growers understand how efficient their watering strategies are. In the realm of grape growing there are many watering strategies that can be used, from sprinkler irrigation, to above surface drip irrigation, to sub-surface drip irrigation, each differing in WUE. From the data collected and analyzed, it was shown that the eddy covariance technique can be used to reliably measure WUE of a vineyard. The calculated average daytime WUE for the Ciel du Cheval vineyard was found to be – 4.53 mg CO2 g ^-1 H₂O. Influence from environmental factors on WUE is evident. Obtaining additional data including soil moisture, irrigation schedule, incoming solar radiation, and canopy temperature would be helpful for further analysis. Future studies from this research hope to deploy eddy covariance towers over multiple vineyards with different watering strategies to compare the efficiencies of those different watering strategies.