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. Patty Skinkis is a professor and viticulture extension specialist in the Department of Horticulture at Oregon State University and member of the Oregon Wine Research Institute. She has prepared the update for the project below.

This work is being conducted with collaboration from Dr. Paul Schreiner, research plant physiologist, USDA-ARS and Andy Gallagher, Red Hills Soils.

In addition to the OWB grant, support was provided by Erath Family Foundation for soil moisture sensors and equipment. Fruit Growers Lab, Inc. donated tissue nutrient analysis services.

Characterizing Willamette Valley Soil Moisture and Grapevine Response under Drying Seasonal Conditions

Project objectives:

  1. Characterize soil moisture conditions throughout the season among different soil types common to Willamette Valley wine grape production.
  2. Determine vine water status, growth, and berry development response to weather and soil moisture conditions throughout the season among different soil types.

Importance to the Oregon wine community:
Most Oregon vineyard businesses do not have budgets to support soil moisture and plant water stress monitoring and often are making best-guess estimates on when to initiate irrigation or vineyard floor management practices that influence soil moisture. This project will generate regionally-specific information about soil water content, climatic conditions, and the impacts of these factors on vine growth that will aid others (e.g., growers, management companies, consultants) to determine best management practices.

Progress so far:
Soil moisture, weather data, and vine growth responses were measured in 2020 in a Pinot noir vineyard that had vines of the same age, clone, and rootstock growing on three soil types, including Saum (volcanic), Dupee (sedimentary), and Willamette-Woodburn (marine sediments). Sensors measured soil moisture, soil temperature, and electrical conductivity at two monitoring locations per soil type to a depth of 18 and 36 inches under-vine and in the middle of the alley between rows.

Soil moisture remained relatively consistent through spring, with soil moisture decline starting mid-June, shortly after bloom, and continuing through summer. Soil moisture decline was greatest at the 18” depth. Willamette-Woodburn soil had the greatest decline in soil moisture yet the largest vine size (based on dormant pruning weight), suggesting that the higher vigor vines in that soil type required more water from the soil profile than vines in the other two soils.

There were no clear differences in vine water stress of the three soil types. Berry weight lagged slightly for vines in Willamette-Woodburn, but there were no differences in the berry development curve. By harvest, yields were similar from each soil type. However, the Willamette-Woodburn had lower Brix and sugar per berry compared to the other two soils. Willamette-Woodburn vines also had greater tissue N at véraison and berry YAN at harvest compared to vines in the other two soils. Since the site was not irrigated and no fertilizers added, the differences in growth and berry composition reflect differences in soil fertility and moisture.

Next steps:
We will continue to this project through the 2021 and 2022 growing seasons. Results of the study will be summarized and compared with other soil moisture monitoring efforts in other Willamette Valley research blocks and with the local technical group to determine how the research compares with other vineyards in the region. We will develop future research projects that will build upon foundational knowledge gained from this study (e.g., timing and type of vineyard floor practices).