Interactive effects of pruning systems and deficit irrigation methods on productivity and phenolic composition of Zinfandel under prolonged drought

Abstract

A trial was conducted in the hot climate of central California to assess the interactive effects of pruning systems and deficit irrigation methods on canopy architecture, yield, water productivity and phenolic composition of Zinfandel under exceptional drought. Pruning systems were cane-pruned (CP, six-canes with 8-nodes), spur-pruned (SP, 22, two-node spurs) and mechanically-pruned (MP, 100 mm hedge). Deficit irrigation treatments were sustained deficit irrigation (SDI) receiving 80% of crop evapotranspiration (ETc) from bud-break to leaf fall, and regulated deficit irrigation (RDI) receiving 80%, 50%, and 80% of ETc between bud-break and fruit set, fruit set to veraison and veraison to leaf fall, respectively. Research vineyard received 87% and 30% of the ten year average of winter precipitation in year 1 and year 2 of the study. In year 1, combination of CP and RDI was recommended based on reproductive and reduced water footprint. In year 2, combination of MP and SDI was recommended based on sustainable yield, optimum leaf area to fruit ratio and increased flavonol, flavan-3-ol monomers, and anthocyanin concentration in berry skin. Productivity indices (leaf area to fruit ratio and Ravaz Index) were adjusted based on results for this hot climate region to reach commercial maturity for the cultivar studied. The study provides information for growers in identifying combinations of pruning systems and deficit irrigation methods that can optimize reproductive, vegetative and water productivity while accumulating commercially acceptable flavonol, flavan-3-ol monomers and anthocyanin concentration in berry skin in hot climate under exceptional drought.