Irrigation management is the focus of many research projects in Washington, and rightly so. Research has guided wine grape growers on how to optimize timing and amount of irrigation needed to improve wine quality, but until recently, little research has focused on the quality of the water used for irrigation.
Grapevines need good quality water for vineyard health, high-quality fruit and sustainable productivity. Long-term use of low-quality water can cause the buildup of salts and sodium in the soil and lead to soil decline and degradation.
Once soils have a salinity or sodicity problem, remedial steps can be daunting because of the time and expense needed to correct issues.
New research supported by the wine industry through the Washington State Wine Commission will help growers deal with declining soil and vineyard health due to salinity and sodicity.
The project, initiated in 2016, includes a survey of vineyard soils and their water sources to assess the extent of salinity and sodicity. Joan Davenport, a Washington State University soil scientist who is leading the project, will also evaluate treatment strategies for affected vineyards and develop management guidelines.
Soil and water quality problems often show up years after planting a vineyard and can be difficult to treat in an established vineyard, which is why Davenport says, growers are always advised to sample their soil and water source before planting and ideally before purchasing.
“I’ve had people come in with soil samples from sites they just bought, and before even planting, they have a problem,” Davenport said. “Had they known what they were up against, they could have avoided the purchase.”
“It’s the water”
Vineyards in eastern Washington are irrigated using either surface or ground water sources. Most of the deep wells contain high concentrations of carbonates, bicarbonates and sodium, and have the potential to be a problem, according to Davenport.
In recent years, growers have increasingly brought soil sample results to her and requested help with struggling vineyards where test results indicate that the soils are saline and or sodic.
All natural water sources contain some level of dissolved ions and suspended particles, she reported. For example, fresh water can contain as little as 50 parts per million of total dissolved solids compared to 35,000 ppm in ocean water. These dissolved solids become a problem when they can’t be taken up by the plants, precipitated or leached out, and accumulate in the soil.
Salts commonly found in irrigation water are sodium chloride, calcium sulfate, magnesium sulfate and sodium bicarbonate. Potassium, nitrate and boron can be present in some water sources.
Wine grape toxicity
Saline soils can adversely affect the growth of wine grapes by affecting soil infiltration rate and soil texture. In high concentrations, salts can be toxic to wine grapes and cause root and leaf burning and slow down metabolic activities.
Salts containing sodium or chloride can inhibit vine growth and cause leaf necrosis, a symptom of chlorosis, which reduces photosynthetic capability and leads to delayed fruit maturity, reduced sugar accumulation and smaller berry size.
Sodic soils may result in poor water infiltration and lead to formation of clay pans and may result in sodium induced deficiencies of calcium, magnesium and even potassium. Although sodic conditions may not produce visible symptoms in the vineyard or detectable changes in fruit phenolic composition, sodicity has been associated with sensory changes in the wine.
The use of deficit irrigation in Eastern Washington vineyards can accelerate the development of the problem. Davenport said, explaining that the volume of water used in deficit irrigation is usually not enough to flush the salts past the root zone.
Also, drip irrigation increases evaporative demand, which causes upward water flow (capillary rise) and further increases concentration of salts in the upper soil profile. “If the water used for flushing is the same water source that created the problem, it can exacerbate things,” she said.
In the first year of the project, Davenport’s lab analyzed soil and water samples from 29 vineyard blocks and 22 water sources.
The survey included red and white wine grape cultivars from vineyards with known or suspected problems in four regions: Columbia Valley, Horse Heaven Hills, Red Mountain and Yakima Valley. The survey will continue in 2017 with new locations added and repeat sampling in the spring and fall.
Thus far, most of the soil and water quality problems seem to be related to sodium.
Sodium, measured by exchangeable sodium percent, was significantly above the recommended range of 15 percent exchangeable soil percentage, or ESP, (at which soils are considered sodic) in more than 30 percent of the samples collected from soils irrigated by groundwater.
Some were as high as nearly 20 percent ESP. But none of the soil samples collected were above levels associated with saline soils.
In the water samples, higher pH and electrical conductivity (EC) levels were found in groundwater compared to surface water, with the exception of a few vineyards with high pH and EC in surface water located at the “end of the line” of the irrigation canal.
Groundwater samples also had significantly higher loads of sodium compared to surface water — concentrations high enough that the vineyard sites are likely to see increased problems, Davenport reported.
Davenport’s three-year project includes a research trial to evaluate different soil treatments to mitigate salinity and sodicity.
Her research will result in guidelines to help growers monitor soil and water for salinity and sodicity and identify symptoms in plants and soils. The research will recommend management practices.
Water testing tips
In terms of water quality, Davenport says it’s much easier to treat problem water than correct a soil problem caused from using poor quality water. She recommends that growers take the following steps:
—Test the water source before planting (ideally before purchasing a site) to identify plant nutrient additions supplied by the water source and if water supply could have a long-term impact on soil chemistry and quality of vineyard health.
—Use a reputable laboratory to analyze samples.
—Analyze water for pH, EC (electrical conductivity), carbonate/bicarbonate, sodium, calcium, magnesium, potassium, nitrate nitrogen and sulfur.
—For vineyards irrigated with well water, test water every four to five years.
—For vineyards located at the end of the line of surface irrigation, test every four to five years.
—Water treatment is recommended if water supply contains high water pH and high carbonate/bicarbonate.
—Monitor water treatment effectiveness by periodically testing water and soils. •
FOR MORE INFORMATION
Growers concerned about salinity or sodicity may contact Joan Davenport at 509-786-9384 or firstname.lastname@example.org for guidance in how to take soil and water samples and a list of local laboratories for sample analysis.
– by Melissa Hansen, the research program manager for the Washington State Wine Commission.