Deficit irrigation (DI) consists on applying water rates to replace only a percentage of the potential vine evapotranspiration (Intrigliolo and Castel 2010). When the water shortage is applied steadily throughout the season, the DI strategy is known as Sustained Deficit Irrigation (SDI), whereas if applied during specific phenological stages is referred as Regulated Deficit Irrigation (RDI). The latter is a particularly promising management irrigation technique in arid and semiarid areas as it offers greater potential to increase water use efficiency (WUE) and improve berry and wine quality (Fereres and Soriano 2007). Numerous DI studies carried out under different edaphoclimatic and experimental conditions, with several winegrapes varieties-rootstocks combinations and with different RDI strategies tested and water volumes applied have revealed significant improvements in WUE and berry quality, although also with yield losses compared to conventional or standard irrigation, sustained deficit irrigation and full irrigation practices. Moreover, it must be noted that the application of irrigation in the vineyard is usually performed by efficient technologies such as pressurized irrigation systems (Keller 2005) and therefore dependent on significant energy inputs for its pumping In this regard, it should be borne in mind that any reduction in irrigation water to the vineyard will lead to energy savings.

The physiological base of DI approaches consists in apply irrigation based upon optimum water status in order to maintain vine water status within the range of optimum thresholds proposed (Romero et al. 2013). On the other hand, the principle of RDI is that plant sensitivity to water stress, in terms of yield and berry quality, is different depending on vine phenological stage and the severity of the stress imposed (McCarthy et al. 2002). If water deficit is applied from fruit set to veraison (pre-veraison water deficit) it will mainly control berry size and reduce vine vigor (McCarthy et al. 2002). If applied after veraison, during berry ripening (Phase III), (post-veraison water deficit) it will mainly increase the biosynthesis of anthocyanins and other phenolic compounds (Castellarin et al. 2007). In general, pre-veraison water deficit is more effective than post-veraison water deficit in reducing berry growth (Levin et al. 2020). Pre-veraison water deficit can also accelerate berry color change (Herrera and Castellarin 2016). Both pre- and post-veraison water deficits have the potential to benefit berry and wine quality in different ways, including: 1) a reduced berry weight and size and higher skin/pulp ratio, 2) an improvement in the cluster microclimate (due to reduced canopy leaf area and more open canopies), 3) altered endogenous hormonal response (e.g. increased abscisic acid (ABA) in roots, leaves and/or berries), 4) changes in root to shoot ratio and/or 5) greater gene expression regulating flavonoid biosynthesis.

The effect of RDI depends on the phenological stage and the severity of the stress imposed in each stage, which in turn is variety specific (Mirás-Avalos and Intrigliolo 2017). An efficient scheduling of RDI requires maintaining the soil and plant water status within a narrow tolerance range, and defining several optimum thresholds values for soil–plant stress indicators to avoid severe root and leaf function damage and drastic yield and berry quality losses (Gambetta et al. 2020). Nonetheless, these indicators depend on the iso/anisohydric behavior of the variety resulting from its interaction with the environment.

Negative carryover effects of some RDI strategies can be also important to maximize grapevine yields or to maintain a sustained long-term high productivity is the main goal (Buesa et al. 2017). A recent study in 15 field-grown grapevine varieties reported that pre-veraison water deficits not only reduced yield in the current season by reducing berry size but can also reduce yield the following season by reducing bud fruitfulness through a reduction in clusters vine^-1 (Levin et al. 2020). Thus, to maximize grapevine yields, water should be applied early to avoid pre-veraison water deficits that can inhibit berry growth in the current season and bud fruitfulness for the following season (Levin et al. 2020). Probably, pre-veraison water deficits of Ψ_leaf averaged ≥ -1.5 MPa (as reported in Levin´s study, - 1.5 to -1.6 MPa), indicator of severe water stress, was enough to disrupt development of cluster primordia in the bud.

As a general guide, most of RDI strategies that have shown benefits apply moderate or low seasonal irrigation water volumes, between 50 and 150 mm season^-1. Besides, the physiologically based irrigation scheduling studies carried out in different grapevine varieties and edaphoclimatic conditions have found significant correlations between midday Ψ_stem and berry quality components and have showed Ψ_stem as a suitable physiological indicator to apply accurate water supply and irrigation scheduling in RDI winegrapes. These studies have revealed that by maintaining moderate levels of mid-day stem water potential, within an optimum Ψ_stem within -1.2 and -1.4 MPa (never Ψ_s ≥ -1.4 MPa) during the pre- and post-veraison periods (mainly from fruit set to harvest) could improve WUE, berry quality and irrigation management in RDI grapevines (Romero et al. 2013; Levin et al. 2020). Moreover, the decoupling between grape primary metabolism (e.g. synthesis of sugars) and secondary metabolism (e.g. synthesis of phenolic substances) observed in field-grown grapevines under heat stress (Sadras and Moran 2012), may also suggest that RDI strategies will have to be adapted to new climatic conditions as consequence of global warming to minimize these undesirable effects on berry quality.

Other additional factors that may be important in increasing irrigation efficiency and vineyard performance under DI strategies, are the frequency of irrigation, emitter spacing and water distribution patterns, and water volume applied in each irrigation (discharge flow rate). The effect of irrigation frequency seems to be more relevant than that of emitter spacing and water distribution pattern (Sebastian et al. 2016). The results obtained in Syrah vineyards indicate that applying a small irrigation dose with a high irrigation frequency (every 2 days) in a heavy clay soil may lead to an efficiency loss (compared to every 4 days). This is because as the wetted soil volume created is small and close to the soil surface it favors soil water evaporation, overall under low water irrigation volume (137 mm season^-1) as usually applied in DI strategies (Sebastian et al. 2015). Besides, under low water availability conditions, plant irrigated every 4 days had higher average net assimilation than plants irrigated every 2 days (Sebastian et al. 2016). In contrast, in table grapes in sandy soils more frequently irrigation resulted more beneficial than low irrigation frequency (Myburgh 2012). These contrasts evidence the need to adapt the agronomic design of the irrigation system to the particular conditions of each vineyard (soil texture and depth, meteorology, irrigation water characteristics, rootstock, etc.) as well as of course, to the winemaking objective.

Moreover, the economic evaluation of the irrigation system must be carried out before adopting any irrigation strategy. In this sense, the energy efficiency of the pressurized system plays a crucial role. Both proper hydraulic design and maintenance are essential for effective operation (Moreno et al. 2016). Simple actions such as cleaning filters and emitters periodically are key to achieving energy savings and ensuring optimal operating pressures. In this regard, it is worth noting the usefulness that soil moisture sensors can have in monitoring the application efficiency of irrigation (Intrigliolo and Castel 2006). But also improve the scheduling time and frequency of irrigation by adjusting the soil profile recharge where the roots are active and avoiding excessive water percolation. Finally, modelling of irrigation systems can also play an important role in precision irrigation, as it allows the determination of irrigation water application uniformity (González-Perea et al. 2018).

Related document(s)

Buesa, I., Pérez, D., Castel, J., Intrigliolo, D.S., Castel, J.R. (2017). Effect of deficit irrigation on vine performance and grape composition of Vitis vinifera L. cv. Muscat of Alexandria. Australian Journal of Grape and Wine Research 23, 251-259.

Castellarin S.D., Matthews, M.A., Di Gaspero, G.D. and Gambetta, G.A. (2007). Water deficits accelerate ripening and induce changes in gene expresión regulating flavonoid biosynthesis in grape berries. Planta 227, 101-112.

Fereres, E. and Soriano, M.A. (2007). Deficit irrigation for reducing agricultural water use. Journal of Experimental Botany, 58, 147-159.

Gambetta, G.A., Herrera, J.C., Dayer, S., Feng, Q., Hochberg, U. and Castellarin, S.D. (2020). Grapevine drought stress physiology: towards an integrative definition of drought tolerance. Journal of Experimental Botany.

González-Perea, R., Daccache, A., Rodríguez-Díaz, J.A., Camacho-Poyato, E. and Knox, J.W. (2018). Modelling impacts of precision irrigation on crop yield and in-field water management. Precision Agriculture 19(3): 497-512.

Herrera, J.C. and Castellarin, S.D. (2016). Preveraison water deficit accelerates berry color change in Merlot grapevines. Am J Enol Vitic. 67, 356-360.

Intrigliolo, D. and Castel, J. (2006). Vine and soil-based measures of water status in a Tempranillo vineyard. VITIS-Journal of Grapevine Research 45(4): 157.

Keller, M. (2005). Deficit irrigation and vine mineral nutrition. American Journal of Enology and Viticulture 56(3): 267-283.

Levin, A., Mathews, M.A. and Williams, L. (2020). Impact of pre-veraison water deficits on the yield components of 15 winegrape cultivars. American Journal of Enology and Viticulture (in press) doi: 10.5344/ajev.2020.19073.

McCarthy, M.G., Lveys, B.R., Dry, P. R. and Stoll, M. (2002). Regulated deficit irrigation and partial root zone drying as irrigation management techniques for grapevines. Deficit irrigation practices. FAO Water Reports Nº.22. Rome, Italy.

Mirás‐Avalos, J.M. and Intrigliolo, D.S. (2017). Grape Composition under abiotic constrains: Water Stress and Salinity. Frontiers in Plant Science. 8, 851‐872.

Moreno, M. A.; del Castillo, A.; Montero, J.; Tarjuelo, J. M. and Ballesteros, R. (2016). Optimisation of the design of pressurised irrigation systems for irregular shaped plots. Biosystems Engineering 151, 361–373.

Myburgh, P.A. (2012). Comparing irrigation systems and strategies for table grapes in the weathered granite-gneiss soils of the lower Orange River region. S. Afr. J. Enol. Vitic. 33, 184-197.

Romero, P., Gil-Muñoz, R., Del Amor, F., Valdés, E., Fernández-Fernández, J.I. and Martínez-Cutillas, A. (2013). Regulated deficit irrigation based upon optimum water status improves phenolic composition in Monastrell grapes and wines. Agr. Water Manage. 121, 85-101.

Sadras, V.O. and Moran, M.A. (2012). Elevated temperature decouples anthocyanins and sugars in berries of Shiraz and Cabernet Franc. Australian Journal of Grape and Wine Research 18(2): 115–122.

Santesteban, L.G. (2019). Precision viticulture and advanced analytics. A short review. Food Chemistry 279: 58-62.