Delayed irrigation nearly doubles yield loss compared to anthocyanin gain in Southern Oregon Pinot noir

Abstract

Irrigation initiation timing is a critical annual management decision that has cascading effects on grapevine productivity and wine quality. A three-year multilocation trial was conducted to optimize irrigation initiation timing using midday stem water potential (Ψstem) thresholds. Plant material, vine and row spacing, and trellising systems were concomitant among sites, while vine age, soil type, and pruning systems varied. Five target Ψstem thresholds were arranged in an RCBD and replicated eight times at each site: -0.7, -0.9, -1.1, -1.3, and -1.5 MPa (T1, T2, T3, T4, and T5, respectively). When thresholds were reached, plots were irrigated weekly at 70% ETc. Yield components, berry chemistry, and anthocyanins were quantified at harvest. Across sites and years, irrigation was initiated at Ψstem = -0.69, -0.96, -1.15, -1.38, and -1.40 MPa for T1, T2, T3, T4, and T5, respectively. Consistent significant linear trends were found for key yield and berry quality parameters across sites and years. Yield decreased by 6.2, 16.9, 24.4, and 34.0% for T2, T3, T4, and T5, respectively, compared to T1 across sites and years that were driven by similarly linear reductions in berry weight and to a lesser extent clusters per vine. Comparatively, berry chemistry variables (Brix, pH, TA) responded weakly and/or inconsistently to treatments across sites and years. However, berry anthocyanin response to treatments was consistent and significant across all sites, increasing linearly with delayed irrigation initiation. Regression analyses of percent change relative to T1 revealed that for every 0.1 MPa of delay past -0.7 MPa, yield decreased by 4.2% (R2 = 0.71, p < 0.001) and anthocyanins increased by 2.3% (R2 = 0.47, p = 0.005) with no change in Brix nor differences among years. Because producers are paid by weight, and contracts typically stipulate a target maturity level, results suggest that there may not be an economic incentive to delay irrigation initiation regardless of vineyard site.