Different spatial distributions of soil moisture were imposed on field-grown grapevines by applying the same irrigation volumes to the entire (DI; deficit irrigation) or part of the (PRD; partial root zone drying) root zone. Five treatments were applied: controls irrigated at 60% ETc (crop evapotranspiration) for the whole season (308 mm year⁻¹); DI-1 and PRD-1 that received the same irrigation as controls before fruit set, 30% ETc from fruit set to harvest and 45% ETc post-harvest (192 mm year⁻¹); and DI-2 and PRD-2 that were the same, except that 15% ETc was applied from fruit set to harvest (142 mm year⁻¹). Compared with DI-1, PRD-1 maintained higher leaf area post-veraison and increased root water uptake, whole-plant hydraulic conductance, leaf transpiration, stomatal conductance, and photosynthesis, but decreased intrinsic gas exchange efficiency without causing differences in leaf xylem abscisic acid (ABA) concentration. Compared with DI-2, PRD-2 increased leaf xylem ABA concentration and decreased root water uptake, whole-plant hydraulic conductance, leaf transpiration, stomatal conductance, and photosynthesis, mainly at the beginning of PRD cycles. Distinctive PRD effects (e.g. greater stomatal closure) depended on the volumetric soil water content of the wet root zone, as predicted from a model of root-to-shoot ABA signalling.

In many areas of southern Europe, the scarcity of water due to climate change will increase, making its availability for irrigation an even more limiting factor for agriculture. One of the main necessary measures of adaptation of the vineyards in these areas will be the implementation of water-saving irrigation strategies and technologies to improve WUE (water use efficiency). The objective of the present study was to evaluate the long-term economic viability/profitability of different deficit irrigation techniques such as regulated deficit irrigation (RDI) and partial root-zone irrigation (PRI) with low water volume/fertilizer applied in a Monastrell vineyard in southeastern Spain to plants grafted on different rootstocks, and to assess the productive, social, and economic efficiency in these semiarid conditions. Through a cost/benefit analysis, socio-economic and environmental criteria for the selection of optimal deficit irrigation strategies and tolerant/water use efficient rootstocks for the vineyards in arid environments are proposed. Our analysis shows a clear conflict between productivity and quality in wine grape production. Productive and economic indices, such as yield, productive WUE (kg m⁻³), economic efficiency (€ m⁻³), break-even point (kg ha⁻¹), and water productivity (€ m⁻³), were inversely related with berry quality. Besides, high berry quality was closely related with higher production costs. Under the current market of low-priced grapes, if the grower is not rewarded for the quality of the grapes (considering technological, phenolic, and nutraceutical quality), the productivity vision will continue and the cost-effective option will be to produce a lot of grapes, even if at the expense of the berry and wine quality. In this situation, it will be difficult to implement optimized deficit irrigation strategies and sustainable irrigation water use, and the pressure on water resources will increase in semiarid areas. Public policies should encourage vine growers to invest in producing high-quality grapes as a differentiating character, as well as to develop agronomic practices that are environmentally and socially sustainable, by the grapes more adjusted to their real quality and production costs. Only in this way we can implement agronomic measures such as optimized low-input DI (deficit irrigation) techniques and the use of efficient rootstocks to improve WUE and grape quality in semiarid regions in a context of climate change and water-limiting conditions.

Regulated deficit irrigation (RDI) and partial root zone irrigation (PRI) were compared for 4 years at two irrigation volumes (110 mm year–1 (1) and 78 mm year–1 (2)) in field-grown grafted Monastrell grapevines (Vitis vitifera L.) to distinguish the effects of deficit irrigation from specific PRI effects. PRI-1 and RDI-1 vines received ~30% of the crop evapotranspiration (ETc) from budburst to fruit set, 13–15% from fruit set to veraison and 20% from veraison to harvest. RDI-2 and PRI-2 vines received around 20% of ETc from budburst to fruit set, no irrigation from fruit set to veraison, and recovery (21–24% ETc) thereafter. Compared with RDI-1, PRI-1 increased irrigation depth and total soil water (?v) availability in the root zone, and stimulated greater fine root growth and water uptake. Increased soil volume exploration supported greater canopy water use, vegetative development, biomass accumulation and internal water storage capacity. PRI-1 vines had higher stomatal conductance, lower leaf-level water use efficiency and increased leaf xylem sap concentration ([X-ABA]leaf) following reirrigation. Compared with RDI-2, PRI-2 decreased total ?v availability, fine root growth and water uptake, gas exchange, leaf water status, [X-ABA]leaf, biomass accumulation and storage capacity. Xylem ABA decreased with total ?v availability in PRI-2, probably from limited sap flow when ?v in drying soil was low (˜20%). For this rootstock–scion combination, high irrigation volumes applied to the wet part of the roots (?v > 30%) are critical for increasing root-to-shoot ABA signalling and growth, and improving performance under semiarid conditions.