Ecohydrological investigation of an alluvial plain vineyard in Precenicco (Italy)

In recent summers, there has been an increase in torrid periods and droughts in the Mediterranean area due to climate changes, leading to a more common use of emergency irrigation in viticulture and reinforcing the need to achieve a more sustainable use of the water resources. In this context, by tracking water in the soil-plant-atmosphere continuum using δ18O and δ2H isotopic values and monitoring water potential in the soil and vines during the growing season, it is possible to understand the water dynamics in the soil, the depth of root water uptake, the water status of the vines, and in the end evaluate the water requirements of the vineyard to achieve a more rational irrigation. In the Interreg Ita-Slo Acquavitis project, this ecohydrological method was applied on six vineyards between Italy and Slovenia. Here we present the results for a vineyard (Vitis vinifera L. cv. Glera) in Precenicco (Friuli-Venezia Giulia, NE Italy). The vineyard is located on the silty-clay alluvial deposits of the Low Tagliamento plain, an area characterized by the presence of multi-layered confined and artesian aquifer systems. Precipitations are abundant in autumn while summers are usually hot and dry (average annual precipitation: 900 ÷ 1000 mm/year). Monthly precipitations were sampled from April 2020 to December 2021. The sampling campaigns for soil (down to 120 cm), xylem sap and water potentials were conducted in the summers of 2020 and 2021. Surface waters and groundwaters samples were collected from a ditch and some wells in the area. During the summer 2021 the vineyard was irrigated three times, and the irrigation water was sampled. The isotopic composition of the water samples was analyzed using an IRMS and a CRDS. The CRDS was also coupled with an induction module to extract and analyze soil water and to analyze xylem sap samples extracted in the field with a vacuum system. The isotopic and water potential data suggest that during the summer of 2020 the vines root water uptake occurred mainly at the most superficial soil layers as in June they were almost saturated by the heavy rainfall. In August and September 2020, the topsoil appeared to have greater water availability than the deeper soil, due to the frequent, albeit scarcer, precipitation occurred in those months. In 2021, we observed a progressive negativization of soil water and xylem sap isotopic values due to the growing contribution of irrigation as a water source.