Abstract Shayla NikzadJean-Jacques LambertZibran ChausChristopher ParryAndrew McElroneAndre KnoesenDavid Block

Using Mass Balance to Determine Plant Water Status of Individual Grape Vines

Shayla Nikzad, Jean-Jacques Lambert, Zibran Chaus, Christopher Parry, Andrew McElrone, Andre Knoesen, and David Block*  
*University of California at Davis, One Shields Avenue, Davis, CA 95616 (deblock@ucdavis.edu)

Bulk irrigation is the status quo in vineyards. However, even when comparing vines planted side by side, irrigation needs may vary dramatically. Additionally, berry quality may be improved by decreasing this heterogeneity between vines. For these reasons, along with the increasing scarcity of water resources in California grapegrowing regions, there is a need to increase the resolution of vineyard irrigation. However, traditional methods of measuring plant water stress (i.e., pressure bomb, porometry, and soil moisture sensing) pose major complications when applied to individual vines. This manifests itself either in the inability of these methods to function at such a high resolution, or in the labor-intensive nature of taking single-vine measurements. Our work focuses on detecting the evapotranspiration rate of individual grapevines using a mass balance approach. Four individually potted vines were placed on load cells. Each vine was outfitted with four humidity sensors and a single anemometer. Two of the four vines were watered with 
48 kg of water, while the remaining two vines were watered with 36kg of water only, every ten days to simulate variable water stress. From budbreak, the relative humidity, wind speed through the canopy, and mass of each potted vine were re-corded continuously. Estimated values of evapotranspiration were calculated from a mass balance using the vine canopy as a control volume. These estimated values were compared to the absolute measurement of lost water mass recorded by the load cell. Additionally, the mass balance estimates were compared to continuous soil moisture measurements and porometric and pressure bomb data taken once and twice a day, respectively. This work is a continuation of a similar experiment conducted on a single vine, in which evapotranspiration rates calculated via mass balance showed agreement with the evapotranspiration rates from the load cell. 

Funding Support: Cypress Semiconductor, Ernest Gallo Endowed Chair in Viticulture, and Till Guldimann