CORVALLIS, Ore. – Oregon wine grape growers in southern Oregon may be able to cut their water usage by almost half, according to an Oregon State University study.
Alexander Levin, assistant professor and viticulturist at the Southern Oregon Research and Extension Center, found that wine grape water usage estimated by the U.S. Bureau of Reclamation’s AgriMet network for irrigation was 44% higher than necessary. AgriMet is a free weather station widely used by growers to determine how much water they need to irrigate their crops.
AgriMet estimates wine grapes need 20.2 inches of water per year in southern Oregon. In his study, Levin estimated annual wine grape needs at 11.4 inches annually, depending on time of year – a vast difference for water-starved southern Oregon, which is already bracing for another drought.
“Federal recommendations are built into the weather station and network,” Levin said. “The network attempts to simplify irrigation scheduling for farmers. We use it regularly for our research. It provides the basic values for them to determine their irrigation needs.”
In southern Oregon – stretching from south of Eugene to the California state line – 9,242 acres were planted with 25,000 tons of wine grapes in 2019, an amount valued at $50 million, according to the Oregon Vineyard and Winery Report by the University of Oregon. When the value of wine is considered, the worth of southern Oregon wine grapes sits right around $238 million, Levin said.
Levin conducted his research at two vineyards in Jackson County, Ore., from 2017-2019. Using solar panels, he estimated the vines’ evapotranspiration – the amount of water transferred from land and plants to the atmosphere. First, he placed the solar panel next to the grapevines in full sun. The same solar panel was then placed under the vines so that part of the panel was shaded. The panel gave a reading of the power produced by the sun compared to shade. This results in a value called a crop coefficient. Growers plug it into a mathematical equation to make irrigation adjustments for different crops.
Well-watered and maintained turfgrass is used as a reference crop because it covers the ground and needs more water than most crops. With grapes, there’s less evapotranspiration and less need for water than for turf.
Using the measurement Levin made between solar power when the panel is in the sun as opposed to the power generated in the shade under the vines results in a number called a crop coefficient. Growers plug it into a mathematical equation to make the irrigation adjustments for different crops.
As the growing season progresses, vineyard water requirements change with grapevine canopy growth and warmer, drier conditions, Levin said. Many growers in the Pacific Northwest already use personal or publicly available weather stations like AgriMet. However, the crop coefficients used for irrigation scheduling were developed in California, where crop growth, cultural practices and water requirements differ.
“The California-based coefficients don’t quite match the pattern of plant growth and development we have her in Oregon,” Levin said. “When the crop coefficient maxes out, you’d expect that to be when the canopies are done growing. They should match. The coefficients developed in California work well in California – better than we expected. But we noticed they weren’t matching what we saw on the ground in Oregon.”
Current values for grapevine water requirements either lack precision or were developed in other regions characterized with different growing conditions. For growers to establish sustainable irrigation practices, they need improved crop coefficients that take into consideration management practices and climate, Levin said.
“We accepted both hypotheses that new regional estimates of coefficients are more accurate and have the potential to result in increased irrigation efficiency and significant water savings,” Levin said. “Ultimately, the improved accuracy of the new estimated coefficient values should allow growers to optimize irrigation scheduling for improved fruit and wine quality.”
About the OSU Extension Service: The Oregon State University Extension Service shares research-based knowledge with people and communities in Oregon’s 36 counties. OSU Extension addresses issues that matter to urban and rural Oregonians. OSU Extension’s partnerships and programs contribute to a healthy, prosperous and sustainable future for Oregon.