**5. Conclusions**

Grapevines exhibit a vigorous vegetative growth between budbreak and veraison [162] and as consequence, the plant has its highest demand for water during this period. If there is an ample availability of soil water that might be supplemented with occasional rains, the plant grows a dense, shaded canopy at expense of reproductive berries with negative impacts on fruit and wine quality potential, foster pests and diseases, and the grower has to resort to expensive canopy management such as shoot and leaf thinning, hedging, and shoot repositioning to correct the canopy architecture and manipulate the plant yield [163]. Attending the effects of these contrasting conditions, a degree of water stress is considered beneficial for the

The use of irrigation in these increasingly stressful environments is a mitigating solution to maintain quality in wine production, minimize the most serious risks of drought damage, and

Under RDI, plant water status is maintained within limits of deficit during certain phases of the seasonal development, normally when fruit growth is least sensitive to water reductions [167]; then, RDI at early stage of grapevine development looks more promising than in later stages. RDI has become widely adopted in the production of wine grapes in arid and semiarid areas [168] and several works have shown that it brings better results than simple DI or FI.

The demand for vineyard irrigation is on the rise as climate becomes more stressful but water is scarcer and the competition among stakeholders becomes acute, factors that require an

In Alto Douro region, the highest water use efficiency (WUE) was reached in rainfed grapevines at expense of yields that were economically unsustainable because the benefits of irrigation were disproportional to the amount of water necessary to bring them about [152, 169]. To strike a balance between yields, berry quality and WUE, it is advisable to impose a moderate stress before veraison but after fruit setting. Pre-veraison RDI compared to SDI reduces vine water use and increases the canopy WUE, decreases the berry polyphenolic but might lower

There is no consensus among the various authors regarding the accumulation and concentration of important metabolites because it depends on skin to pulp ratio in berries [171] as smaller berries favor their concentration in the must. The soluble solids that determine the alcohol content in wine, was found to be more concentrated in grapevines subjected to SDI than in rainfed or abundantly irrigated plants [172], while others found a lower concentration under very restricted DI [153] or did not find any significant difference in their concentration [173]. These contradictory results might be related to the accuracy of vine water status monitoring necessary to regulate and manage the physiological changes imposed to the vines by DI [83]. In other words, DI might be beneficial if an accurate control of water deficits is

Studies have shown that changes in grapevine water status, at selected and critical phenological stages, are as important as the amount of water applied on influencing vegetative

production of quality grapes [164, 165].

68 Irrigation in Agroecosystems

improvement in the efficiency of water use.

the financial return due to lower yields [170].

*4.3.3. Effect on berries quality*

exerted [94].

in extreme cases, guarantee plant survival [151, 166].

The recommended irrigation strategy should be the one that maintains better tree water status throughout the season, depending on the soil water content at the beginning and the availability of water. These factors change between years, so deficit irrigation studies should be carried out for longer time than 2 or 3 years to produce a better knowledge of water stress effects.

For the above reasons, and based on the successful use of RDI in fruit trees and grapevines reviewed herein, the adoption of RDI strategies in water-limited areas should be encouraged.

So, it is of great importance to bear in mind that results depend mainly on cultivar, orchard characteristics, environmental conditions, and agronomic practices and to the large variability in rainfall, climate, and soil types between the various growing regions; thus caution must be taken when applying the findings reported by different authors to a particular orchard.
