Water Management of Irrigated Cabernet Sauvignon Grapevines in Semi-Arid Areas

The effect of four years of deficit irrigation on water savings, yield, crop load, plant growth, and juice composition was determined on Cabernet Sauvignon grapes grown on the Central Coast of California. The growing season was divided into three periods. The first was from budburst to fruit set, during which there was no irrigation. The second was from fruit set to three weeks post-fruit set, during which 75% of calculated crop water use (ETc) was applied for all treatments. The third began three weeks post-fruit set and continued to harvest, during which irrigation resumed whenever the leaf water potential (LWP) reached -1.2 MPa in one of three sustained deficit irrigation treatments equal to 25/35% (LOW), 50% (MED), and 75/65% (HIGH) of ETc. The sum of rainfall and irrigation applied during the growing season ranged from 91 to 196 mm, from 145 to 234 mm, and from 198 to 273 mm for the LOW, MED, and HIGH treatments, respectively. Total water use, including soil water during the growing season, ranged from 250 to 359 mm, 288 to 418 mm, and 313 to 378 mm for the LOW, MED, and HIGH treatments, respectively. Yield was linearly related to the sum of irrigation and rain and to the total available water (rain, irrigation, and stored soil water) during the growing season. Yield was consistently lower in the LOW treatment across all years than in the MED and HIGH treatments; while yields in the MED and HIGH treatments were not different. Average pruning weight and cane weight declined in all treatments over the four years of the study, as did average berry size. Berry and wine composition was not affected by irrigation treatment within a given year, but were different across years due to climate, irrigation schedules, and harvest dates. Our results illustrate potential applied water savings during the growing season with moderate deficit irrigation (i.e., MED), with minimal or no significant effect on fruit yield and juice composition, while severe reduction of applied water (i.e., LOW) led to loss of yield without changing juice composition and would not be considered economically sustainable.