Can soil water content be used as a predictor of predawn leaf water potential for deficit irrigation scheduling? A case study at Alentejo wine region

Abstract

Context and purpose of the study: Water and heat stress impose new challenges to irrigation management in the Mediterranean areas. This reality has a major impact on the vineyard ecosystem, particularly on the scarce water resources of the Alentejo region (South Portugal). To mitigate this problem, irrigation management should focus on optimizing yield and fruit quality per volume of water applied. This work aims to discuss the use of predawn leaf water potential and soil water status relationships as a decision tool for irrigation management taking as basis data from a field trial where two deficit irrigation strategies were compared.

Material and methods: A deficit irrigation experiment was conducted from 2013-2015 at a commercial vineyard locatedat Reguengos de Monsaraz, Alentejo, Portugal (38o22’ N 7o33’ W) with the V. vinifera variety Aragonez (syn. Tempranillo). A sustained deficit irrigation (DI) strategy used by the farm consisting of a constant proportion of crop evapotranspiration (0.28) was applied along the irrigation period (DI1) and was compared with DI2, a similar strategy but with 48% lower water volumes than DI1, using a randomized complete block design with four replications of 15 plants. Predawn leaf water potential (ψPD) was used to define the beginning of each irrigation event.Soil water content until one meter depth was assessed and the fraction of transpirable soil water (FTSW) was calculated. Yield, berry composition and pruning weight were assessed. This paper reports the first year (2013) results.

Results: The DI strategies induced a decrease of ψPD along the season. In parallel, the progressive water withhold decreased FTSW (accessed after each irrigation event) along the season from 80 to 20%, while atmospheric water demand was increasing. The strong correlation between ψPD and FTSW observed may support the use of FTSW as a robust predictor of ψPD. The stressful conditions imposed by this irrigation strategy had no significant effect on yield, berry composition and vigor. The crop WUE (amount of fruit produced per unit of water applied) was higher for DI2 strategy and, at the same time, allowing water savings as compared to grower’s irrigation strategy.