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The effects of two regulated deficit-irrigation (RDI) strategies pre- and postveraison on soil-plant water relations and their influence on leaf area development, cluster microclimate, yield, and berry quality were evaluated during two years in field-grown Monastrell grapevines under semiarid conditions in southeastern Spain. Three treatments were applied. The control was irrigated at 60% ETc (crop evapotranspiration), or 319 mm water over the full season. Regulated deficit-irrigation treatment 1 (RDI-1) received the same irrigation as the control before fruit set, 30% ETc from fruit set to harvest, and 45% ETc postharvest. Regulated deficit-irrigation treatment 2 (RDI-2) was the same as RDI-1, but with 15% ETc from fruit set to harvest. RDI-1 maintained soil water content and vine water status adequate for sustaining leaf gas exchange, without affecting sugar accumulation or increasing polyphenols at harvest. Moreover, RDI-1 reduced yield and berry size and improved cluster microclimate by reducing leaf area and increased water use efficiency. However, RDI-2 suffered more stress, mainly postveraison. This severe water stress substantially reduced root-vine hydraulic conductance and leaf gas exchange, decreasing gas exchange efficiency, leaf nitrogen, and chlorophyll content. Excessive postveraison water stress advanced leaf abscission, reducing leaf area development and yield. Lower leaf photosynthesis and higher leaf abscission significantly decreased yield and sugar in RDI-2 berries compared with RDI-1. Polyphenol and anthocyanin content also decreased significantly in RDI-2 compared with RDI-1. To avoid severe root and leaf function damage and increase polyphenols in this cultivar, we identified optimum physiological thresholds for several vine water indicators pre- and postveraison.
Romero et al. (2010) studied this question.