The Interactive Effect of Pruning Level and Irrigation Strategy on Water Use Efficiency of Vitis vinifera L. cv. Shiraz

A partial rootzone drying (PRD) irrigation technique (0.5 ML/ha) was compared with a standard irrigation treatment(1 ML/ha) at three different pruning levels of 30, 60 and 120 nodes per grapevine in Vitis vinifera L. cv Shiraz. The PRDirrigation technique was applied to a single side of the grapevine rootzone at a time, 45 cm from the trunk, and the sideswere switched in 10-day cycles. For the standard irrigation treatment, both sides of the grapevine were irrigated. At theend of an irrigation cycle, the PRD treatment resulted in reduced midday readings of stomatal conductance and stem (ψS)and leaf (ψL) water potential relative to the control treatment. During the switch between irrigation cycles, when the soilwater profile of both the ‘wet’ and ‘dry’ sides of the PRD-treated grapevines was refilled, stomatal conductance, ψS andψL were restored to the same levels as for the control experiment. As node number per grapevine increased, berry size andwinter pruning weight were reduced and yield increased. In the first season of the experiment, the PRD treatment did nothave a significant effect on berry size, yield and pruning weight, although shoot length was reduced in response to PRD forall the pruning treatments. In a subsequent season, PRD was found to reduce yield, primarily through a reduction in berryset. Water use efficiency measured as t/ML irrigation water applied was increased significantly as crop load increased, andwas enhanced in response to the PRD irrigation technique.