Effect of different timings and intensities of water stress on yield and berry composition of grapevine (cv. Sauvignon blanc) in a mountain environment
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Irrigation is becoming an extremely important practice for mountain viticulture to guarantee the quality of the production in a climate change scenario. The aim of this work was to relate the degree and the timing of water stress caused by limited soil water availability to the performance of field-grown Sauvignon blanc vines. The 2-year trial (2014–2015) was conducted in a terraced Sauvignon blanc vineyard located in a coarse-textured soil of South Tyrol, Italian Alps, at 500 m altitude. Treatments were: full irrigation (FI), corresponding to the standard farm irrigation approach; deficit irrigation (DI), corresponding to half of the FI water volume; rain fed (RF), not irrigated. In year 2014, the drought period was short and intense, lasting for approximately 15 days during flowering. The reduction of the number of berries per bunch was severe in RF vines, leading to a strong limitation of the final yield per vine. A rainfall above the seasonal average for the study area in summer 2014 (post veraison phases) allowed, despite the average berry weight reduction, DI vines to reach a final yield that did not differ as compared to FI. Year 2015 was much dryer, with a drought period lasting from blooming to approximately 20 days after veraison. Both RF and DI vines were severely affected by water shortage as indicated by different physiological indexes (pre-dawn leaf water potential, leaf gas exchanges) and growth, yield and grape maturation process were impaired. Results indicate that under the described experimental conditions, water stress that occurred in the period before and around fruit set, with pre-dawn leaf water potential (Ψpd) lower than −0.7 MPa, severely reduced the final number of berries per cluster. A deficit irrigation regime in the same phenological stage was able to reduce the intensity of water stress (Ψpd around −0.4 MPa) and did not affect the fruit set process. Increasing water stress intensity between fruit set and veraison (up to a Ψpd of −0.9 MPa) progressively depressed berry weight and quality. This work underlines that under the unpredictable climatic conditions that characterized mountain environment, a strict control of the vine and soil water balance is needed for a successful management of deficit irrigation systems.