Project Summary
Delaying irrigation initiation can have many positive direct and indirect effects on grapevine growth and development, and ultimately on fruit and wine quality. The overall objective of this research project is to determine the optimal irrigation initiation time using declining stem water potential thresholds and relating grape yield and berry composition metrices to those thresholds. Our central hypothesis is that growers can substantially delay irrigation initiation time without any negative effects on current or future production.
Project objectives:
The overall objective of this research project is to determine the optimal irrigation initiation time by:
- Delaying initiation time using declining stem water potential thresholds; and
- Relating crop yield and quality metrics to those thresholds.
Our central hypothesis is that growers can substantially delay irrigation initiation time without any negative effects on current or future production, ultimately improving vineyard water use efficiency.
Importance to the Oregon wine community:
When to initiate irrigation is a critical annual management decision that has a large impact on the current season’s production. Delaying irrigation initiation can have many positive direct and indirect effects on grapevine growth and development, and ultimately on fruit and wine quality. Thus, it is economically favorable to delay the initiation of irrigation just enough to create a slight water deficit.
Other funding sources: Oregon Department of Agriculture, Rogue Valley Winegrowers Association
Progress Reports
2020-21: Year 1 Update
In its 2020-21 fiscal year, the Oregon Wine Board of Directors granted $350,000 to researchers for eight projects with the potential to advance quality grape growing and winemaking in Oregon. The update below is part of a series to let you know about the status of these projects.
Progress so far
At present, the pilot phase of the project has been successfully completed. Sites that represent a transect of soils and climates were identified and assessed for field variability. Using midday stem water potential (ψstem) data collected at veraison in 2020, statistical analyses were conducted to assess presence of spatial variability of selected blocks at each site. The pilot ψstem data were used to identify ideal experimental design using pre-determined levels of precision. Experimental plots were laid out at all three sites, and custom irrigation systems have been installed. All sites are ready for the experimental phase of the project to be conducted in the 2021 and 2022 growing seasons.
Next steps
Weekly ψstem data collection will begin approximately 30 days after bud break (mid-May) at all sites. It is anticipated that earliest initiation timing will be in late-May and latest initiation timing will be in mid- to late-July (depending on site). Vine productivity and fruit composition data will be collected at harvest in late-September.
2021-22: Year 2 Update
In its 2021-22 fiscal year, the Oregon Wine Board of Directors granted $289,000 to researchers for six projects with the potential to advance quality grape growing and winemaking in Oregon. The update below is part of a series to let industry members know about the status of these projects.
Progress so far
At present, the first year of the project has been successfully completed. Irrigation treatments were successfully applied at each of the three trial sites. As expected, there were large differences among sites with respect to grapevine dry-down dynamics – vines at the first site dried down early and quickly (all treatments initiated in June), vines at the second site dried down late and quickly (all treatments initiated in July), while vines the third site dried down slowly over the course of the growing season (treatments initiated over a 9-week period from June to August). Total amounts of applied water accordingly depended on site and treatment and ranged from 2.4 to 9.1 inches. ψstem values at initiation ranged from -0.7 to -1.5 MPa. Berry size and ultimately yield were strongly and linearly reduced with delays in irrigation initiation at each site. Both Brix at harvest and wine anthocyanins increased with slight delays in initiation, then decreased with further delays.
Next steps
Analyses of fruit and wine flavonoid composition in response to treatments is ongoing, as well as those of fruit and wine tannins. Experimental trial is being repeated in 2022, and carryover effects will be noted from 2021 water stress.
Other funding sources: Oregon Department of Agriculture, Rogue Valley Winegrowers Association
Principal Investigator
Dr. Alexander Levin is a viticulturist at the Southern Oregon Research and Extension Center, an assistant professor in the Department of Horticulture at Oregon State University, and a core faculty member of the Oregon Wine Research Institute. He has prepared the update below.
