Use of sap-flow sensors to schedule vineyard irrigation. I. Effects of post-veraison water deficits on water relations, vine growth, and yield of Shiraz grapevines

Different levels of irrigation based on transpiration data measured using s ap-flow sensors were applied after veraison to Shiraz grapevines grown on a two-wire vertical trellis in the Barossa Valley, Australia. Data for the v ines of the upper and lower wire were studied separately. The intensity and duration of stress in each treatment was expressed as a water stress integ ral (S psi) from the predawn leaf water potentials. Leaf area, yield and po st-veraison water use of vines in the different treatments was closely rela ted to S psi. Irrigation increased grape yields and differences in vine wat er status after veraison led to differences in the leaf area to fruit weigh t ratio. it was concluded that data from the sap-flow sensors could be used as a basis for calculating irrigation amounts to influence vine water stat us, canopy size, and grape yield.