CORVALLIS, Ore. — Wine grape growers in Southern Oregon might be able to cut their irrigation water use by almost half, according to an Oregon State University study.
“We found that new regional estimates are more accurate and have the potential to result in increased irrigation efficiency and significant water savings. The improved accuracy should allow growers to optimize irrigation scheduling for better fruit and wine quality.”
Alec Levin, OSU Extension viticulturist at the Southern Oregon Research and Extension Center, found that water use estimates from the U.S. Bureau of Reclamation’s AgriMet weather station network were 44% higher than necessary. AgriMet is a free, widely used tool for determining crop irrigation needs.
AgriMet estimates that wine grapes in Southern Oregon need 20.2 inches of water per year. Levin’s research, however, found that annual needs are closer to 11.4 inches — depending on the time of year.
He conducted the study at two Jackson County vineyards from 2017 to 2019. Using solar panels, Levin measured evapotranspiration — the amount of water transferred from soil and plants to the atmosphere.
The process involved placing a solar panel in full sun next to grapevines, and then placing it under the canopy where part of it was shaded. Comparing the energy output from sun and shade produced a “crop coefficient,” a number growers use in irrigation formulas to adjust watering needs for different crops.
Wine grapes need less water than turfgrass
In irrigation science, well-watered turfgrass is often used as a reference crop because it covers the ground completely and requires more water than most crops. Grapevines, by contrast, have less leaf area and lower evapotranspiration, so they require less water.
Many Pacific Northwest growers already use AgriMet or other weather stations for irrigation scheduling. However, Levin noted that the crop coefficients in AgriMet were developed in California, where plant growth patterns, vineyard practices, and climate differ from Oregon.
“The California-based coefficients don’t quite match the pattern of plant growth and development we have here in Oregon,” Levin said. “They work well in California — better than we expected — but we noticed they didn’t match what we saw in the vineyard here.”
The potential for significant water savings
Southern Oregon — stretching from south of Eugene to the California border — had 9,242 acres of wine grapes producing 25,000 tons in 2019, valued at $50 million, according to the Oregon Vineyard and Winery Report by the University of Oregon. When the value of the wine is included, the region’s wine grape industry is worth about $238 million, Levin said.
By adopting regional crop coefficients that reflect local growing conditions, growers could improve irrigation efficiency, conserve water during drought years, and maintain or improve fruit and wine quality.
“We found that new regional estimates are more accurate and have the potential to result in increased irrigation efficiency and significant water savings,” Levin said. “The improved accuracy should allow growers to optimize irrigation scheduling for better fruit and wine quality.”
Previously titled Southern Oregon wine grapes may need less water, OSU Extension study shows
