Monitoring Grapevine Water Status at the Regional Scale of the San Joaquin Valley Using Remotely-Sensed Actual ET
Kaylah Vasquez, Eve Laroche-Pinel, and Luca
Brillante*
*Department of Viticulture and Enology, California State
University Fresno, 2360 E Barstow Ave, Fresno, CA, 93740
(lucabrillante@csufresno.edu)
Water insecurity, as a result of erratic environmental behavior, has become a familiar concern for growers across California and water restriction has increased demand for precision farming techniques. Satellite sensors can provide useful information in space and time to monitor vegetation characteristics, as multispectral imagery can inform about plant composition and structure. This project aims to validate if the application of a spatial model of energy balance and actual evapotranspiration from satellite images and agrometeorological data can be used by growers to monitor grapevine water status in the San Joaquin Valley. In 2021, we selected 50 experimental units of Chardonnay grapevines in five vineyards located in different counties across the San Joaquin Valley. We selected the location of experimental units by maximum dissimilarity sampling based on soil texture and hydraulic conductivity obtained from the USDA-SSURGO database and normalized difference vegetation index measured in late spring of the same year from Landsat 8. We geolocated all experimental units and assessed grapevine water status at the end of ripening by measuring the carbon isotope discrimination (δ13C) of grape juice at harvest. To estimate actual grapevine evapotranspiration, we applied the simple algorithm for evapotranspiration retrieving (SAFER) model based on satellite imagery from Landsat 8, reference evapotranspiration and solar radiation from the spatial version of CIMIS (California irrigation management information system), and average temperature from the PRISM (parameter-elevation regressions on independent slopes model) climate mapping system. Finally, we compared pixel-level actual evapotranspiration to carbon isotope discrimination to evaluate the ability of model estimates to assess grapevine water status and inform irrigation decisions.
Funding Support: ARI-HSI
