A Pinch of This, a Dash of That

The Importance of Understanding Micronutrients in Grapes

By Brian Charles Clark
wine.wsu.edu

When humans don’t get enough zinc, we can get sick with cancer and suffer immune-system dysfunction. The same is true of plants. Micronutrients such as boron, zinc and copper, although only a tiny part of a plant’s diet, can have a profound effect on the plant’s health.

Washington State University soil scientist Joan Davenport and her colleagues at the WSU Irrigated Agriculture Research and Extension Center in Prosser are studying micronutrient utilization in Concord grapes. Washington is the nation’s number one Concord grape producer, so understanding what happens with micronutrients is important to the industry’s bottom line. And what Davenport learns about micronutrients in Concords is going to be applicable to wine grapes, too.

Micronutrient availability is an issue in Washington’s grape-growing region, with its high pH soils. The soil availability of micronutrients decreases as pH increases.

“Right now, growers apply micronutrients based on their experience and on what’s commercially available. We want to give them quantifiable data to work with,” said Davenport. “Then they’ll be able to supply plants with what they optimally utilize without spending more than they need to on inputs.”

If the vine doesn’t get enough boron, Davenport said, pollen lands on the flower but doesn’t germinate. “That’s a disaster,” she said, “because if there’s no pollination, there’s no seed, and then there’s no fruit.” Copper and zinc don’t affect the plants so dramatically, but do affect the size of the canopy.

Davenport’s current project is based on one that her doctoral student, Suphasuk “Bird” Pradubsuck, finished recently.

“Bird excavated Concord vines at various times during the growing season and then did detailed and comprehensive analysis of the plant parts in order to ascertain the amounts per acre of micronutrients the plants used,” Davenport explained.

Macronutrients, such as nitrogen, are measured in pounds per acre, while micronutrients are generally measured in parts per million. “A typical Concord yield is about eight tons per acre,” said Davenport, “To get that, the plants need about fifty pounds of nitrogen per acre, but only a third of a pound of boron.”

Davenport is running extensive field trials on micronutrient utilization with a cooperating grower. “We’re putting on micronutrient fertilizers as both ground and foliar applications,” she said, in order to determine whether vines take up the nutrients from the soil or through their leaves.

Davenport’s research has direct impact on wine-grape growing as well. She and her team are imposing nutrient deficiencies on Cabernet Sauvignon and Semillon grapes.

“All micronutrients have different M.O.’s. By depriving plants of individual nutrients, we’ll be able to see what affects they have and, with the field study data, compare the results in ways that inform wine-grape growers. It’s all about yield and quality,” said Davenport.