The effect of water stress applied alternately to part of the wetting zone along the season (PRD-partial rootzone drying) on wine quality, yield and water relations of red wine grapes

Three levels of irrigation regimes were applied during three successive years to a 6 year old Vitis vinifera L. ev. Merlot vineyard grafted onto 1108 rootstock. The vineyard is located at the Kibbutz Yiftakh commercial vineyard in the upper Galilee region of Israel at an elevation of 350 m on a deep gromosol soil. The three irrigation levels applied by drip irrigation consisted of 0.15, 0.28, and 0.55 average seasonal class A pan evaporation coefficient respectively. The seasonal accumulated water applied varied between 120 to 450 mm, equivalent to 50, 100 and 200% respectively of the commercial recommendation for wine grapes in this region. Each irrigation levels was applied by both one and 2 lateral lines per row. The two lateral treatment was applied in a PRD mode, namely alternating the irrigation between the two sides of the vines approximately every two weeks whereas the one lateral per row served as a control. The six treatments were applied in a 5, randomized block design with 10 vines per replicate. The following measurements and analyses were made: Crop level, pruning weight, crop load, number of clusters, berry number and weight, Brix, TA, pH, midday stem water potential. Soil water content and potential was measured by a Neutron scattering device. Wine was prepared from each replicate by microvinification. Sensory evaluation by an experienced panel as well as volatile GC-MS analyses were conducted. Results of all measured parameters showed no significant effect of PRD. Significant effects of the irrigation levels on many parameters were found among the three experimental years. The results of this study contradict reports of other field experiments where proper control treatments were not implemented. A thorough literature review of root physiology mechanisms leads to a conclusion that drip irrigation principles are based on partial root drying and therefore alternating irrigation between vines sides are not expected to have any advantage under field conditions. The difference between short time split root container experiments under controlled conditions and field experiments will be discussed.