Good Fruit Grower

January 15

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16 JANUARY 15, 2016 Good Fruit Grower L ow water years pose addi- tional challenges for Pacific Northwest Concord growers, who are already dealing with low prices. However, there are steps growers can take to ensure their vineyards remain healthy — even in a tight water year — at the most critical points during the season. The first step is to know as much as possible about the vineyard's soil, according to Jason Stout, a post-doc- toral research assistant at Washington State University's Irrigated Agriculture Research and Extension Center in Prosser. At the Washington State Grape Society's annual meeting in November, Stout reminded growers that soil texture determines the field capacity and perma- nent wilting point in their vineyards — and the sweet spot for repeated irrigation throughout the season. Field capacity (FC) is the total amount of water a soil can hold. Soil is typically at FC one to two days after a heavy rain or immediately after irrigation when no standing water is left on the soil surface. Any water added above the FC will not stay in the root zone, but will drain due to gravity. The permanent wilting point (PWP) is reached when water content is too low for the plant to remove water from the soil, or the water is too tightly bound by the soil to be extracted by the plant, and the plant cannot recover from the deficit. The amount of water between FC and PWP is your plant-available water. "You don't want to apply above the field capacity, because that's a waste. You lose that water," Stout said. "And you want to know your permanent wilting point and the range at which you need to reapply water, which is typically when you reach 50 percent of the plant-avail- able water." With Concords, unlike wine grapes, growers want to minimize stress levels as much as possible to maximize yields. Testing soil moisture to determine water needs is better than applying a set amount on a weekly schedule. by Shannon Dininny WATERING Concords Grapes

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