David Copeland discusses the crush pad mechanics at Zirkle Wine Company in Prosser during a summer grape field day. Zirkle Wine is one of Washington State’s newest and largest custom crush wineries. Photo by Melissa Hansen

David Copeland discusses the crush pad mechanics at Zirkle Wine Company in Prosser during a summer grape field day. Zirkle Wine is one of Washington State’s newest and largest custom crush wineries. Photo by Melissa Hansen

For years, vineyardists in the Pacific Northwest have followed California recommendations to sample leaf petioles at bloom to assess the nutrient status of vines. But at Washington State University’s grape field day this summer, growers learned that a different timing and sampling technique are needed for their cooler Northwest climate. “The best time for us to sample is not at bloom, like in California, but at veraison,” said Dr. Joan Davenport, WSU soil scientist.

Recent WSU research involving several years of tissue-sample analysis shows that for the Pacific Inland Northwest region (Washington, Idaho, and Oregon), the whole leaf—blade and petiole—should be analyzed, not just the petiole, as in California.

Additionally, research found that veraison was the best time to sample in Northwest vineyards. When Davenport compared Northwest nitrate levels with California nutrient standards, the Northwest -samples were almost always deficient in nitrogen. Her work led to new critical values for grape leaf concentrations in Washington and Oregon. She will soon have vineyard nutrient values developed for Northwest soils. She believes there are several reasons why the Northwest plant tissue samples appeared on paper to be -deficient in nitrogen.

For one, soils in eastern Washington usually stay cool until bloom time, which would reduce plant nutrient uptake. “Also, Northwest growers may not have started irrigation before bloom and the nutrients may not yet be moving into the plant,” she explains.

Moreover, her research showed that whole leaves were better for sampling because petiole analysis was inconsistent in the irrigated Pacific Northwest. “And, whole leaves are much easier to work with than petioles because they are not time-of-day sensitive,” Davenport said. Nutrient concentrations at veraison were stable and bloom samples far less so, she stated, adding that a downside to the veraison timing is that the results come too late to make significant changes in the current season. “But it will help you in planning your nutrition for next season.”

She advised growers who have traditionally sampled plant tissue at bloom time to continue for a year or two while adding the veraison timing until a baseline for nutrient status has been developed. “Do a complete nutrient analysis on your plant tissue samples every year,” Davenport recommended. “A lot of what the plant needs are macronutrients like nitrogen, phosphorus, and such, but sometimes micronutrients like zinc and boron can be low, especially in high pH soils that limit their availability. If you are applying boron, it can be tricky because too much can be phytotoxic.”

Soil nutrient levels don’t need to be analyzed as often as plant tissue. She suggests taking a soil sample every three to five years. Growers should be sure to use a laboratory that participates in proficiency testing, a voluntary quality control program that compares lab procedure and analysis against industry standards. Costs for soil and plant tissue analyses are generally less than $50 per sample and -discounts are often given for multiple samples.

Optimizing irrigation

Dr. Markus Keller has spent the last three years studying optimal irrigation treatments as part of his long-term research to develop strategies to maximize production of a fully mechanized juice grape vineyard. With support from the Washington State Concord Research Council and Wyckoff Farms, the WSU viticulturist uses an eight-acre Concord block planted in 2003 to conduct a variety of trials, including spacing and plant density and -minimal pruning. He has studied seven different irrigation treatments on the minimally pruned vines to identify irrigation practices that would maximize long-term -productivity and fruit quality, and reduce annual yield variation.

“When I came to Washington State in 2001, I was a wine grape guy—I knew nothing about juice grapes,” he said. “But I saw juice grape growers spending too much money in labor and water for the returns they were getting back.” He began looking for ways to reduce costs while maintaining productivity and quality. In his irrigation study, control vines are subjected to full irrigation; early deficit (75% and 50% evapotranspiration) from fruit set to veraison; late deficit using full irrigation until after veraison, then reducing to 75 and 50 percent ET; and full-season deficit, irrigating at 75 and 50 percent ET during the entire fruit development period.

Thus far, he’s found that irrigation treatments of 75 percent ET are similar to 100 percent ET. But when 50 percent ET is applied, berries were smaller, and crop yields were reduced by 15 percent. “Applying a water deficit before veraison limited berry size and compensation for smaller berries was not possible by applying more water after veraison,” he said at the field day. “If you’re short at the front end, you can’t apply more water later in an attempt to plump up berry size. If you want big berries, the critical time is to apply water from fruit set to veraison.”

Heavy watering during ripening to maintain berry size may not be as important as was previously thought, Keller added. Irrigation treatments have not affected juice composition (soluble solids, titratable acidity, pH, and color). “Irrigation treatments do influence berry size, while temperature impacts the harvest date,” he said. The field day, sponsored by WSU’s Viticulture and Enology Program and the Washington State Grape Society, also toured WSU’s grape powdery mildew block where ongoing efficacy, epidemiology, and modeling studies take place, and had an inside look at Zirkle Wine Company in Prosser, one of Washington’s newest and largest custom crush facilities. •

A free WSU extension publication on nutrient sampling and recommendations for irrigated vineyards in the Pacific Northwest can be downloaded from:  http://cru.cahe.wsu.edu/CEPublications/PNW622/PNW622.pdf

Sampling tips

Washington State University researchers recently updated nutrient sampling guidelines for wine and juice grapes grown in the Pacific Northwest. Dr. Joan Davenport, WSU soil scientist, provided the following soil and plant tissue sampling tips during a summer grape field day.

Process—Use the same sampling techniques for both juice and wine grapes.

Timing—Best time to sample plant tissue is when 40 to 60 percent of the berries have reached veraison (the onset of ripening when grapes begin changing color). Soil samples can be taken at same time.

Frequency—Take plant tissue samples annually and run a full nutrient panel; soil samples can be taken every three to five years unless you’re trying to make -significant changes through soils amendments.

What to sample—Collect whole leaves (blade and petiole) for tissue samples. Soil core samples should be taken 18 inches deep.

Sample containers—Use paper bags for plant tissue samples and sealable plastic bags for soil. Leaves will be dried and ground at lab, so samples don’t need to be kept moist. However, soil should be kept moist and chilled if necessary.

How to sample—For a plant tissue sample, collect the fifth leaf inward from the end of a randomly selected shoot. Be sure to sample on both sides of the canopy. For a soil sample, it is easiest to use a soil probe that collects a core of soil, but a shovel will do. Always avoid sampling the edges of the vineyard. Soil sample locations depend on the type of irrigation. For overhead sprinkler irrigation, sample between rows in a zigzag pattern, but avoid sampling from the absolute row middle. Sample every third or more rows. For drip irrigation, sample 8 to 16 inches away from the drip line, never directly below it. For overhead sprinkler irrigated, sample between rows in a zigzag pattern, avoiding row middles.

Number of samples to collect—For plant tissue, collect 50 leaves for the first acre and 25 more leaves for each additional acre, up to a total of 300 leaves per block. Sample red and white varieties separately until you’ve learned which varieties are similar. For soil, collect 25 to 50 cores per blocks of one acre or less. Increase in increments of five cores per acre for up to 100 cores per block. If the block has multiple varieties, keep samples separate.

Mixing soil sample—Place soil cores in a large container or bucket and mix well before putting at least a cup of soil in sealable plastic bag. Label bag with vineyard name, grower name, date, location. Keep cool until delivered to lab.

9 Use a qualified lab—Seek a lab that participates in the North American Proficiency Testing Program, a voluntary quality control program for laboratories. A listing of soil and plant tissue laboratories can be found on WSU’s viticulture and enology Web site at -http://puyallup.wsu.edu/analyticallabs/-services.—M. Hansen