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.
Dr. Alexander Levin is a viticulturist at the Southern Oregon Research and Extension Center, an associate 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.
Determining optimal irrigation initiation time
The overall objective of this proposed research project is to determine the optimal irrigation initiation time by:
- Delaying initiation time using declining stem water potential (ψstem) 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.
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.
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