Effects of irrigation amount on water relations, vegetative growth, yield and fruit composition of Sauvignon blanc grapevines under partial rootzone drying and conventional irrigation in the San Joaquin Valley of California, USA

Abstract

SummaryA study was conducted to investigate the effect of partial rootzone drying (PRD) in comparison to conventional irrigation (CI) at both 0.8 and 0.4 crop evapotranspiration (ETc) on water relations, vegetative growth, yield, and fruit composition of mature Sauvignon blanc grapevines (Vitis vinifera L.) in the San Joaquin Valley of California, USA. Soil moisture decreased quickly on the dry side and was restored quickly on the wet side of PRD-treated vines after switching. There was no yield reduction while vegetative growth was reduced at 0.4 ETc. However, in contrast to published studies assuming and emphasizing the role of PRD, this study demonstrated that only an irrigation amount of 0.4 ETc reduced stomatal conductance, transpiration, pruning weight, number of lateral shoots, number of active growing points, and fruit titratable acidity (TA). It appears that the irrigation amount, not PRD, is the determining factor inducing water stress and reducing transpiration and vegetative growth. With vine water relations only occasionally affected and no improvement in vine performance and vine water use at the same irrigation amount, PRD is not recommended for winegrape production with Sauvignon blanc under similar climatic conditions and cultural practices as in this study. Commercial implementation of PRD as described in previous studies should not be recommended until PRD is proven advantageous over CI at the same irrigation amount.