Drought is a widespread concern globally. Along with temperature increases, water scarcity has created increasing competition for this vital resource. Therefore, adopting sustainable practices to efficiently utilize water in agriculture is crucial, particularly in arid and semi-arid regions. Over the past decades, extensive research has been conducted on water usage in agricultural products, including wine grapes. The water status of grapevines during the growing season plays a dominant role in nutrient uptake, vine vigor, and nutrient source-sink ratio, all of which ultimately affect berry composition and wine quality (Chaves et al., 2010; Hunter, Etchebarne, Ojeda, & Hunter, 2010; Zufferey et al., 2017).
To maximize water productivity, deficit irrigation is frequently practiced on farms to provide crops with less water than their full evapotranspiration needs. Although a slightly lower yield is typical, deficit irrigation often results in higher water use efficiency and improves the sustainable use of water. Deficit irrigation can also impact grape quality by impacting the formation and accumulation of secondary volatiles and volatile precursors in grapes (Koundouras, 2018) in a varietal specific response.
Both the degree and timing of deficit regulation affect vine growth and grape secondary metabolite accumulation; therefore, it is crucial to apply proper deficit irrigation at the optimal time to produce premium wines with minimal loss. While deficit irrigation can be a tool to improve grape quality, excessive water stress can negatively impact vine nutrient uptake and photosynthesis, leading to yield loss and poor grape quality. Therefore, the degree of water stress must be carefully regulated to promote healthy vine growth and high-quality grape production. Despite the potential impact of deficit irrigation, the effects of irrigation quantity and timing, particularly on wine aroma composition, are not well-documented, especially for Pinot noir.
To address this, the influence of delayed irrigation initiation time on the aroma composition and total phenolics of Pinot noir wine was investigated from 2021 to 2023 in three sub-regions with different soil types and climates in Southern Oregon (Ashland, Eagle Point, and Jacksonville). Grapevines were irrigated with 70% evapotranspiration (ETc) at different initiation times based on normalized vine water status thresholds (ΔSWP) throughout berry development. The ΔSWP was defined as the departure of measure midday stem water potential from the calculated non-water-stressed baseline (ΔSWP = SWPns – SWPabs). Wines were made from these grapes, and the volatile compounds in the wine were analyzed. The results showed that delayed initiation of irrigation time impacted the volatile compounds in the wines, although the effects of geographic location and vintage were more significant. Methoxypyrazines, associated with herbal and green aroma attributes, decreased with delayed irrigation in Jacksonville and Eagle Point in all three vintages; however, this trend was not consistent in Ashland. Total esters and total terpene alcohols increased in response to delayed initiation of irrigation at all three sites. β-Damascenone and β-ionone, which are associated with berry aroma attributes, increased in response to delayed irrigation initiation times at the Jacksonville and Ashland sites for all three years. The increase in β-damascenone and β-ionone, combined with the decrease in methoxypyrazines, will likely result in wines with fruitier, berry-like aroma attributes. Further research is underway to investigate the effects of irrigation on aroma precursors in the grapes and grape quality. — By Tingting Ye, Alexander Levin, Yanping Qian, & Michael Qian (Oregon State University)
This research was funded by the USDA-ARS.
Chaves, M. M., Zarrouk, O., Francisco, R., Costa, J. M., Santos, T., Regalado, A. P., Lopes, C. M. (2010). Grapevine under deficit irrigation: hints from physiological and molecular data. Annals of Botany, 105(5), 661-676. https://doi.org/https://doi.org/10.1093/aob/mcq030.
Hunter, J. J., Etchebarne, F., Ojeda, H., & Hunter, J. J. (2010). Leaf: Fruit Ratio and Vine Water Status Effects on Grenache Noir (Vitis vinifera L.) Berry Composition: Water, Sugar, Organic Acids and Cations. South African Journal for Enology and Viticulture, 31, 106-115. https://doi.org/https://doi.org/10.21548/31-2-1407.
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Koundouras, S. (2018). Environmental and Viticultural Effects on Grape Composition and Wine Sensory Properties. Elements, 14(3), 173-178. https://doi.org/https://doi.org/10.2138/gselements.14.3.173.
Zufferey, V., Spring, J.-L., Verdenal, T., Dienes, A., Belcher, S., Lorenzini, F., . . . Viret, O. (2017). The influence of water stress on plant hydraulics, gas exchange, berry composition and quality of Pinot Noir wines in Switzerland. OENO One, 51(1). https://doi.org/https://doi.org/10.20870/oeno-one.2017.51.1.1314.