Carmen Gispert,* Alyssa DeVincentis , Keith Orlebeck, Justin Haessly, and Samuel Sandoval-Solis  
*University of California Cooperative Extension, 81-077 Indio Blvd. Suite H, Indio, CA 92201 (cgispert@ucanr.edu)

The purpose of the study was to develop a regulated deficit irrigation program as a strategy to optimize water use on Tempranillo grapes in the Temecula Valley of California and document the effect of deficit irrigation on juice composition. We are testing the hypothesis that the relationship between soil moisture and leaf water potential in Tempranillo grapes receiving deficit irrigation can be modeled. Three deficit irrigation scheduling treatments, replicated three times, were assigned to blocks of 150 vines in a complete randomized block design. The deficit irrigation treatments were T1: sustained deficit at 50% ET from bud-break through veraison; T2: postveraison deficit at 10% ET at veraison; and T3: preveraison deficit at 10% ET beginning at fruit set. The vines from all treatments were irrigated at 100% ET after harvest. Leaf water potential was measured weekly using a pressure chamber. In most cases, at the time irrigation events took place, the pressure chamber readings were between 11 to 13 bars. The correlation between the water potential and soil moisture was analyzed at 4-inch increments up to 36 inches below the soil surface to determine if soil moisture levels can indicate the stress level of a grapevine. The analysis revealed a negative correlation between leaf water potential and the previous day’s soil moisture at 36 inches below the surface for postveraison and preveraison treatments, while the sustained deficit at 50% ET showed no identifiable relationship. Future research will focus on modeling this relationship to develop a practical deficit irrigation guide based on measureable soil humidity.

Funding Support: California Department of Food and Agriculture