Relationship between Soil and Plant Water Status in Wine Grapes under Various Water Deficit Regimes

Limited water supply in arid and semiarid Mediterranean environments demands improving irrigation efficiency. The purpose of this study was to determine a functional relationship between soil water availability and wine grape ( Vitis vinifera ) water status to determine a threshold value of soil matric potential to trigger irrigation. Seasonal trends of soil water potential, leaf water potential, and stomatal conductance ( g S ) of ‘Tempranillo’ wine grape were determined in two deficit irrigation treatments replenishing 45% and 30% of the reference evapotranspiration, and in a third non-irrigated treatment during 2001 and 2002. Soil water potential was measured with granular matrix soil moisture sensors placed at 0.3 m (Ψ 0.3 ), 0.6 m (Ψ 0.6 ), and 1.2 m (Ψ 1.2 ) depths. The sensors at 0.3 m depth quickly responded to irrigation by increasing Ψ 0.3 levels. At the 0.6 m depth, Ψ 0.6 progressively decreased, showing significant differences between T1 and the rest of the treatments, while no significant differences in Ψ 1.2 were found. All relationships between profile soil matric potential and leaf water potential and g S were highly correlated. After integrating our data with previous studies, we suggest a whole profile soil water potential value of –0.12 MPa as threshold to trigger irrigation and avoid severe water stress during berry growth.