Matthew Jenkins, Konrad Miller, and David Block*
*University of California – Davis, Robert Mondavi Institute - North Building, Block Lab, 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 which affect plant water use, leading to over- and underwatering. To increase water use efficiency, irrigation practices must take 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 for use in most commercial settings. The purpose of this project is to provide proof-of-concept that ET sensors, combined with appropriate, physically-based models, 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. In 2020, we introduced three ET models and discussed their strong correlation with real ET. This presentation explores one of these models, the Convective Mass Transfer model, more closely, discussing the first principles concepts underlying the model and the meaning of each term in the model. Results from the 2021 season compar­ing CMT-model predicted water use rate and real ET provide further evidence that it could be possible to inform irrigation decisions at the previously unthinkable scale of single vines.

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