Matthew Jenkins, Autumn Mannsfeld, Konrad Miller, Jean-Jacques Lambert, Mason Earles, and David Block*
*University of California – Davis, 1 Shields Ave, Davis, CA 95616 (deblock@ucdavis.edu)

As California becomes increasingly affected by drought and water use regulations become more restrictive, the demand for increased water use efficiency grows in importance. Currently, the viticulture industry relies on bulk irrigation, which assumes all vines in a given area have the same water demands. This assumption ignores individual plant health, the heterogeneity of soil, canopies, topography, and many other factors that affect plant water use, leading to over and under-watering. To increase water use efficiency, irrigation practices must take this spatial variation into account. Existing methods for estimating single-vine ET, such as sap flow or aerial imaging, are too expensive and/or technically advanced to use in most commercial settings. The purpose of this project was to provide proof of concept that simple ET sensors, along with appropriate, physically-based models, will allow precise control of irrigation down to single-vine resolution. Four mature Zinfandel vines were potted and placed on load cells in a vineyard setting, as simple weighing lysimeters to accurately measure ET. We then developed three mathematical models, two based on first principles and one empirical model, to predict the mass flow rate of water leaving a single vine based on common biometeorological parameters measured on each of the four vines. To evaluate the utility of each model, we compared the predicted mass flow rate of water out of a grapevine to load cell-derived ground truth ET data. We report a strong correlation between all models’ predicted water use rate and real water use rate (r2 = 0.78 to 0.88). Predicted water use rates can be used to accurately calculate single vine ET, thereby informing irrigation decisions at the previously unthinkable scale of single vines.

Funding Support: Private gifts; Ernest Gallo Endowed Chair in Viticulture & Enology