Dr. Alexander Levin, asst. professor, Dept. of Horticulture, OSU and OWRI, has prepared the update below. This project receives funding from the Oregon Wine Board as part of its viticulture and enology research grant program.
Importance to the Oregon Wine Community
Competition for freshwater resources is increasing throughout the American West, and there is continued pressure on agricultural producers to conserve water through improved irrigation management practices. Pinot noir is the third most widely planted red wine grape cultivar in the United States and is Oregon’s signature wine grape cultivar. Yet, while it has traditionally been cultivated in cooler and wetter growing regions of the state (e.g. the Willamette Valley), new Pinot noir plantings have occurred in warmer and more arid growing regions, such as the Umpqua and Rogue Valleys of Southern Oregon. Despite increasing acreage in these regions, cultivar-specific drought responses remain poorly elucidated in the literature. Compared to other economically important cultivars, such as Cabernet Sauvignon, there are surprisingly few publications that have addressed Pinot noir responses to water deficits. Therefore, this study has been designed to fill the gap in the literature by establishing a robust field experiment in a mature, commercial Pinot noir vineyard to evaluate yield, fruit quality, and wine quality responses to the timing and severity of water deficits. Providing growers with more information regarding the effects of seasonal water deficits on vine performance is necessary for the optimization of irrigation management strategies that will ultimately reduce water use and improve Pinot noir fruit and wine quality.
A multi-year field experiment was established with eight irrigation treatments designed to alter vine water status either pre- or postveraison. Irrigation was scheduled based on applying water at fractions of estimated crop evapotranspiration (ETc) ranging from 25 to 100%. Vine water status was monitored with regular measurements of midday stem water potential (Ψstem) throughout the growing season. At harvest, fruit were analyzed for yield and quality characteristics, and small-lot wines were made.
The irrigation treatments significantly altered vine water status both pre- and postveraison, giving rise to a broad range of water deficits during both periods. Berry size was negatively correlated with water deficits during both periods. Berry primary metabolism (Brix, pH, and TA) was less sensitive to water deficits relative to secondary metabolism (anthocyanins and tannins). Total anthocyanins increased with water deficits both pre- and postveraison, and the response was more sensitive preveraison, but the differences were not statistically significant across treatments. In contrast, skin and seed tannins were significantly impacted by the treatments. Skin tannins increased with preveraison water deficits but decreased with postveraison water deficits. Seed tannins increased with preveraison water deficits but were not affected by postveraison water deficits.
In general, berry secondary metabolism was more sensitive to preveraison water deficits. However, postveraison water deficits resulted in higher concentrations of secondary metabolites overall. While wine sensory analyses have yet to be completed, the results suggest that postveraison water deficits may be more effective at improving Pinot noir fruit quality without a yield penalty compared to preveraison deficits. Additional years of study will aim to corroborate the first year’s results and will be used to develop irrigation management strategies for Pinot noir that are optimized for production goals.