Irrigation scheduling and management for white wine grape production

By altering the amount of water available to grapevines, irrigation can impact canopy growth, fruit quality and yield, especially in arid and semi-arid regions. Most information about irrigation management has been generated using red wine grape cultivars, therefore, two white cultivars, Chardonnay and Riesling, were used in this study. First, the efficiency of three irrigation scheduling aid tools was compared. These tools were based on (i) evapotranspiration (‘ET’, to replace 100% crop evapotranspiration (ETc), (ii) soil moisture (qv, ‘SOIL’, to maintain qv near field capacity, 16%), and (iii) vine water status (‘PLANT’, to maintain stem water potential (Y_stem) near non-stress levels, -0.7 MPa). For both cultivars, ET received more water than did SOIL and PLANT. Consistently, qv of ET was >16% and its Y_stem was > -0.7 MPa, which resulted in denser canopies, more lateral growth, and larger berries compared with SOIL or PLANT. Although SOIL received more irrigation than PLANT, few differences in vine performance were observed between them. Consequently, water use efficiency was the highest for PLANT and the lowest for ET. Secondly, three deficit irrigation regimes were implemented to optimize irrigation practices. These treatments were (i) moderate water stress from fruit set to harvest (‘SDI’), (ii) moderate water stress from fruit set to véraison, and then no water stress through harvest (‘RDI’), and (iii) partial rootzone drying from fruit set to harvest (‘PRD’). The target levels of qv and Y_stem for moderate water stress were 12% and -1 MPa, respectively. The drying part of the rootzone of PRD was irrigated once qv ≤12%, which led to irrigation being alternated every 2-3 weeks. For Chardonnay, PRD resulted in more canopy growth, higher yield, and larger berries than other regimes. For Riesling, however, few differences in vine performance were found, except that berries of PRD were larger than others. Overall, it showed that ET over-irrigated the vines, because irrigating at <100% ETc was adequate to sustain non-stress levels in qv and Y_stem. Compared with moderate water stress, no stress after véraison did not affect yield, berry size, or berry composition. Moreover, PRD increased yield without affecting berry composition.