Influence of timing and intensity of deficit irrigation on vine vigour, yield and berry and wine composition of 'Tempranillo' in southern Portugal

For most of the Portuguese viticultural regions, winegrape production is subject to high evaporative demands during dry summer leading to increasingly low soil water availability. As a consequence, grapevines normally suffer severe drought stress, affecting negatively yield, wine quality and consequently farmers' income. To sustain an economic productivity, irrigation is an important tool in vineyard management. The objective of this study was to understand how deficit irrigation strategies would influence vine vigour, yield and quality of grapes and wines. During two growing seasons (2008-2009), field grown grapevines (‘Tempranillo’) were studied in southern Portugal. Vines were spur-pruned and trained to a bilateral cordon. Three deficit irrigation treatments were defined, using as reference predawn leaf water potential ((Ψpd): weak water stress (Ψpd<-0.4 MPa); mild water stress (-0.4 MPa>Ψpd>-0.6 MPa); and severe water stress (Ψpd<-0.6 MPa)). All these three treatments were undertaken in traditional tillage. An additional treatment was performed with a cover crop (mild water stress) in order to increase soil moisture depletion in spring, causing an earlier water stress. This last treatment caused a greater reduction on vegetative growth (primary and secondary shoots) and yield. Conversely, an increase of total phenolic compounds was found, probably due to higher sunlight penetration into the canopy. However strong differences were verified between the two years with a reduction in total polyphenols index and anthocyanins content in 2009. This was probably due to negative effect of the very high temperatures during phenolics synthesis. Deficit irrigation treatments also caused significant differences on yield, berry sugar content and total phenolics, as well as in the chromatic and sensorial characteristics of wines. The severe deficit treatment caused defoliation leading to an incomplete maturation and inferior wine quality. On the other hand, the weak deficit treatment originated wines with lower total phenolics. Our results suggest that mild water deficits may benefit fruit composition and wine quality. Furthermore, an earlier water deficit could be a useful strategy to increase the phenolic compounds.