2020-21 OWB Funded Research | Determining optimal irrigation initiation time

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 industry members know about the status of these projects.

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.

This project also receives funding from Rogue Valley Winegrowers Association.

Determining optimal irrigation initiation time

Project objectives:
The overall objective of this research project is to determine the optimal irrigation initiation time by:

1. Delaying initiation time using declining stem water potential thresholds; and
2. 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 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 (ψ_stem) data collected at veraison in 2020, statistical analyses were conducted to assess presence of spatial variability of selected blocks at each site. The pilot ψ_stem 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 ψ_stem 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.