Kaylah Vasquez, Guadalupe Partida, 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)

As drought conditions become more familiar to San Joaquin Valley grapevine growers, the need for effective water management solutions has heightened. Understanding the physiological responses of the plant at various intensities and timings can still provide great context for more advanced developments.

The purpose of this study was to determine the primary effects of sustained and regulated deficit irrigation on plant water status, gas exchange, berry composition, and yield components. We used a single commercial Cabernet Sauvignon × 1103P vineyard located in the West San Joaquin Valley. Irrigation treatments were applied nine times weekly from bunch closure to harvest. Irrigation was applied using a semi-autonomous irrigation approach and actual amounts were recorded through flow meters. The plants were sampled biweekly, starting the week before the first irrigation event. Irrigation treatments were calculated as fractions of the grower’s water allocation, which roughly corresponded to 60% crop evapotranspiration in the middle of the summer. Treatments included sustained deficit irrigation schedules with 40, 60, 80, and 100% of the grower allocation and regulated deficit irrigation strategies with different amounts before and after veraison. RDI treatments were 100/40, 80/60, 60/100, 100/60, 60/80, 80/40, 40/100, and 40/80, where figures express percentages of the grower allocation and are formatted as preveraison allocation/postveraison allocation). In the dry conditions of our study, limited to one single season of observation, we found little to no effect of irrigation amounts on plant physiology, yield, and grape composition. The results of this study did follow the general trends for grapevines in semiarid environments, although continued data acquisition is required to validate the results and observe carryover effects. We also infer that implementing automated irrigation can be effective for irrigating remotely and monitoring true amounts; we do, however, discuss several limitations associated with precision in large blocks.

Funding Support: American Vineyard Foundation; California State University – Agricultural Research Institute