Sustained and regulated deficit irrigation of field-grown Merlot grapevines

Background and Aims: The aim of this research was to examine the effect of sustained and regulated deficit irrigation regimes on vegetative growth, physiological aspects and yield parameters of field-grown Merlot grapevines. Methods and Results: The 4-year trial (2009–2012) in a 13-year-old commercial vineyard of Vitis vinifera cv. Merlot compared the following irrigation treatments: three sustained deficit irrigation treatments and two regulated deficit irrigation treatments. We measured leaf area index and pruning mass to assess vegetative growth, and we recorded stem water potential and gas exchange parameters to examine vine water status. At harvest, we measured yield parameters, crushed berries and analysed must. High water availability during early berry development enhanced vegetative growth and increased berry size and yield. Reducing water supply in order to create a certain level of drought stress during late berry development did not damage yield or berry maturation. Conclusions: Regulated deficit irrigation treatment combining higher irrigation from flowering to bunch closure and lower irrigation from bunch closure to harvest has the potential to generate the best balance between vegetative growth, high yield and wine with enhanced colour and aroma compounds. Significance of the Study: This study demonstrates the implications of skilled irrigation, in particular the specific effect of irrigation alternation at different phenological stages.