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Monday, March 31, 2014, 6:00 am

New tech saps vine water use

Real-time monitoring helps better time, reduce irrigation

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    Fruition Sciences sap monitor on vines at Shafer Vineyards

    Shafer Vineyards put four vine sap-flow monitors like this one on each of two top-end Napa Valley blocks and discovered optimal irrigation timeframes, saving as much as 100,000 gallons of water last year.

    After just one season of watering vines in Shafer Vineyards’ Napa Valley estate property by a relatively new method of tracking real-time data on how much soil moisture they actually need, Director of Winemaking Elias Fernandez estimates he cut water use by as much as 100,000 gallons in just those seven- and five-acre test blocks.

    By having Fruition Sciences install sap-flow sensors on two representative vines in each of the blocks and looking at graphs of how vines reacted to waterings and environmental conditions, Shafer found that it was able to skip two roughly weekly irrigation applications for the larger block and one for the smaller one, Mr. Fernandez said. At about four gallons of water for each vine and thousands of vines per block, each application adds up.

    Elias Fernandez, winemaker, Shafer Vineyards

    Elias Fernandez

    “All this is to make better wine and not just conserve water,” he said. “We want small berries, but we also want vines that survive and get grapes to maturity.”

    Limiting the size of the grape cluster berries is desirable for maximizing color and flavor, particularly for Shafer’s Stags Leap district vineyard that supplies Shafer’s signature cabernet sauvignon wine, Hillside Select, which retails for $240 a bottle.

    Controlling how much water vines get via irrigation is part of a delicate viticultural dance between coaxing vines to enhance grape development and leaving the plants susceptible to damage from extreme heat waves. Too thirsty, and vines can reduce grape yield and have challenges recovering. Slaked too much, and vines can divert too much of their resources to foliage and larger berry sizes.

    The tools of farming grapes have gone high tech in the past several years, including GIS mapping of vineyards and Internet-connected weather stations. But tools for measuring vine transpiration — how much sap moves through the plant and evaporates from the leaves — have been less than real-time until recently.

    Common tools for measuring water movement in vines are pressure chambers and leaf porometers. The chambers, often called pressure bombs, require a leaf with stem to be cut from the vine and put into a sealed container with a seal around the stem, and the gas pressure applied to push sap is used to calculate vine water usage. Leaf porometers use an electrical probe to measure stomatal conductance, or how much water vapor is leaving the pores of leaves.

    The wireless sap-flow sensors Fruition Sciences uses use electrical capacitors to generate a tiny amount of heat in an insulated sleeve around a vine arm. Movement of the heated sap through the vine is measured and transmitted to the company’s central computer servers, combined with other vineyard data such as neutron probe soil-moisture readings, pressure bomb samples and weather station data such as temperature, humidity and vapor pressure deficit, a measurement of how much moisture air can hold when saturated. Vine transpiration tends to track with changes in vapor pressure deficit. All this information is stored and made available to the customer via the desktop, tablet or smartphone.

    Mr. Fernandez opted to try the Fruition Sciences data package with sap sensors after using pressure bombs to gauge transpiration for two decades.

    “It is influenced by environmental pressure and humidity,” he said of the pressure-chamber approach.

    Measuring leaf water potential, or how vigorously sap is moving through the vine, with a pressure chamber requires a strict protocol as to the time of day and environmental conditions to ensure no “noise” is introduced to the readings, according to Virginie Mertier, Fruition Sciences director of sales. Because the readings from the sap-flow sensors are continual vs. periodic, the risk of skewed data can be lessened and vine response to heat waves can be measured, she said.

    The key is to select where the sensors are placed in the vineyard to get accurate samples of vine condition based on similarities in soil type, vine variety and other factors, Mr. Fernandez said.

    “We are learning how each soil and variety reacts to translate that information to other vineyards,” he said. “We’re trying to wet the soil profile around the roots of vines. Some soils take more water and some less.”

    Shafer shifted to irrigating from reservoirs in the 1990s, even removing a few acres of vines to do so. Wells had been used for watering for the previous two decades. Now, they are tapped just for winemaking, and the process wastewater is pond-treated and used for irrigation. Last week before the rain storms, Shafer’s reservoirs were full and 80 percent full.

    Fruition Sciences’ installation of sensors and access to data cost Shafer $10,000 for the two vineyard blocks. The vintner plans to add monitoring for two more vineyard blocks this season.

    Generally, the service is an annual license ranging from $50 for d0-it-yourself installation to $5,000 for full-service surveys of the vineyard to find representative sensor sites, or “smart points.” The number of sensors per vineyard can vary widely, with some five-acre properties having four and the largest having the same number for thousands of acres.

    Started in 2007, Fruition Sciences (fruitionsciences.com) started collecting data from Napa Valley vineyards the following year, expanding to Sonoma County, Livermore Valley, France and Argentina. New customers are starting monitoring in the Central Coast. Based in Oakland with offices in St. Helena and France, the company has about 100 customers, 70 of which are in California.

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