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26 APRIL 1, 2016 Good Fruit Grower www.goodfruit.com Subsurface irrigation shows potential for Concords, too. by Shannon Dininny t he first year of a study into subsurface irrigation of Concord grapes — delivering water underground, rather than on the soil surface — shows the technology's potential to produce comparable quan- tities and quality of grapes while saving water at the same time. And those results came during one of the driest and hottest summers in recorded history in Washington. Dr. Pete Jacoby, Washington State University pro- fessor and plant ecologist, conducted the first year of the multiyear study on a block of Concord grapes, established in 2003, at WSU's Irrigated Agriculture Research and Extension Center near Prosser, Wash- ington. The block was divided into 30 plots, each comprised of 30 vines planted on 6-foot (in row) by 9-foot (between rows) spacing. Jacoby placed emitters 18 inches on either side of each vine to deliver water at depths of 1, 2, 3 and 4 feet below the soil surface. Drought conditions in 2015 forced some irrigation districts to ration water to users with junior water rights, and water was withheld at this particular site from mid-May until the second week of June. For that reason, some planned water treatments were deferred in order to saturate the soil with water until normal delivery resumed. However, for the remainder of the growing sea- son, all plots received no less than 75 percent of the replacement evapotranspiration rate during each scheduled irrigation, Jacoby said. At the mid-veraison stage of development, plant water stress was substantially less in plots receiving subsurface irrigation at the 2-foot and 3-foot depths, the study showed, as opposed to the 1-foot and 4-foot depths. In a progress report, Jacoby attributed the difference to excess moisture loss to the understory vegetation as well as to surface evaporation at the surface and 1-foot depth and to the plant's inability to uptake water from 4 feet below the surface due to hardpan conditions. The research team collected grape clusters in late July. They were consistently heavier with increased depth of irrigation delivery. The total numbers of ber- ries were higher for the subsurface treatments than for the control surface drip treatment, and the aver- age berry weight was greatest at the 2-foot and 3-foot depths of water delivery. They collected clusters again Sept. 12 and had similar results, with total berry num- bers slightly higher for all subsurface treatments over the surface drip treatment. The site has a highly variable soil type, including an extremely hard layer of solidified calcium carbonate below the upper 2 feet of the soil profile. This layer may reduce the availability of soil mois- ture and create the need for more frequent irrigation, but that may mean other parts of the vineyard are overwatered at the same time. Vineyards with similar conditions lend themselves to site-specific irrigation technologies as they become available, the report showed. • Concords on DefICIt The Cabernet block, planted on 6-foot (in row) by 8-foot (between rows) spacing in fine, loamy sand, pre- viously had been drip irrigated. Jacoby and his research team installed vertical delivery tubes 18 inches on either side of each vine — rather than buried lines — to deliver water beneath the surface at depths of 1, 2 and 3 feet. Irrigation was applied at reduced rates of 60, 30 and 15 percent of the commercial rate applied by standard sur- face drip irrigation. The researchers also applied water both in a continuous stream and as a pulse to allow the plants to rest between drinks of water. Remote sensors measured plant water stress in late July 2015. At the same time, grape clusters were gathered mid-ripening to determine fruit weight and average number of berries per cluster. In late September 2015, fruit on each vine was harvested and weighed. The commercial irrigation, at a 100 percent supply, resulted in the strongest crop, at 4.5 tons or 10 pounds per vine. But Jacoby said he expected fruit weight to drop significantly with reduced water application, which didn't happen. "I was quite surprised we got as much fruit as we did," he said. The winning rate: 60 percent of the commercial water application rate, which produced 4.1 tons or slightly more than 9 pounds per vine when applied at depths of 2 feet and 3 feet below the surface. The subsurface treatments also produced larger numbers of berries than the commercial treatment, but the berries were smaller, Jacoby said. The results impressed Williams, though he cautioned that these were early results. The vertical application sys- tem still may not enable growers to locate an irrigation problem before the plants are too stressed any more than buried lines do, he said, and more research is needed to At mid-veraison, plant water stress was substantially less in plots receiving subsurface irrigation at the 2-foot and 3-foot depths as opposed to the 1-foot and 4-foot depths. Better Performance, Fewer Applications, Better Cherries. THE RAIN IS COMING. BE PREPARED! Parka forms a food grade, transparent and tasteless cuticle supplement that has been shown to reduce rain cracking by an average of 50%. The unique elasticity of Parka allows a simple 2 application program starting at straw color while avoiding reactive sprays closer to harvest. Save time, money and headaches. Visit cultivaipm.com to find out more. 888.638.1955 www.cultivaipm.com sales@cultivaipm.com Parka can be purchased at your local retailer, contact us for more details. Parka is a trademark of Cultiva, LLC. 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