A small Kawasaki Mule is equipped with sensors and a LIDAR unit for evaluating canopy shape.
—Using irrigation in the vineyard is less about ensuring growth and more about applying the right amount of water at the right time. The same could be said about water conservation in general.
At a recent water conservation workshop organized by staff from Napa County Flood Control and the Water Resources Department in the theater of the former Copia center, several experts discussed ways to reduce water use.
Mark Matthews, a professor with the University of California, Davis
, described a wide-ranging project by professors at Davis and other western universities to develop irrigation systems that use sensors and a central control system to apply water exactly when it’s needed. (See "Precision Sensors Monitor Winegrape Water.")
Matthews said it’s well documented that vines become too vigorous with too much water, resulting in a green sprawl that yields poor-quality grapes. “You can grow a hell of a bunch with too much water and too many nutrients,” he said.
Stressing vines helps produce concentrated clusters that make better wine, he said, pointing to a photo of a vine with yellow leaves but well-formed grapes. “These vines look ragged, and in fact they ripen a crop,” he said. The challenge is creating just enough stress while maintaining enough green leaf surface area to provide photosynthesis and push the grapes past the ripeness finish line.
Mathews said researchers at Davis are experimenting with indirect micrometeorological instruments that constantly monitor the temperature changes and water loss. He said they’re measuring transpiration using a Krypton anemometer that can detect the minute eddies generated from the canopy and infrared cameras can measure leaf temperature.
Researchers are also using a small Kawasaki Mule vehicle equipped with sensors to evaluate the shaded areas of the canopy while a LIDAR system catalogs its shape. A GPS unit and data logger will collect the information so growers “know exactly how much water is needed where.”
Mike Delwiche, also with UC Davis, is working with Camalie Networks’
eKo Pro sensors to develop a sensor-driven irrigation-control system. Sensors monitor soil moisture and relay signals to a control node that can open valves releasing irrigation water. Mathews said a vineyard system would need some type of controls to adjust for applying varying amounts of water to different parts of the row.
Earlier in the month, ratepayers in the Los Carneros Water District that includes the Napa County side of the Carneros AVA approved a rate increase to raise $1.14 million for designing a 9-mile pipeline that will eventually carry water to the region.
If the project passes another round of ratepayer approval after the pipe is designed, growers in the Carneros district could have access to 1,250 acre-feet of recycled water per year.
At the conservation workshop, Dr. Stephen Grattan, a plant-water specialist with the University of California, Davis, described a study he helped conduct to gauge the feasibility of using recycled water for grapevine irrigation.
Grattan tested soil samples from a vineyard that had been irrigated with recycled water for eight years as well as compared water samples from surface and well sources to recycled water. The test revealed nothing of concern with the recycled water.
He said the water posed no significant threat of increasing the salinity or putting vines at risk from chlorine or boron toxicity.
The water, however, would be a “dilute fertilizer” delivering about 14-21 pounds per acre of nitrogen per irrigation season. Grattan said growers using recycled water for irrigation would need to keep that in mind and adjust their cover crops and fertilizer use. “Others, on the other hand, could look on it as a benefit and cut back on nitrogen amendments,” he said.
Extended sheep grazing
Holistic farming expert Kelly Mulville suggested growers could not only improve their vineyard soils but conserve water by allowing sheep to graze in their vineyards.
Mulville described a 2009 vineyard trial in which he kept sheep grazing in a vineyard past bud break. To keep the hungry sheep out of the canopy of the vineyards, Mulville said he installed an electric wire near the fruit zone in the canopy. He said when developing a vineyard for extended grazing it’s necessary to train vines to 52-54 inches to ensure the sheep can not eat the canopy.
Left to their own devices, Mulville said the sheep wander through the vineyard creating paths, causing soil compaction and will actually eat the same patches of weeds repeatedly rather than graze the entire property. Mulville said a herd of about 200 animals per acre should be contained in small areas and then moved methodically through other parts of the property. That ensures the ground can recover, and it better replicates the tight bunching of herd animals in the wild.
After the extended grazing trial, Mulville said the vineyard needed 80% less irrigation, produced 1.2 more tons per acre and the wine made from that vintage tasted better as well. The water savings were actually an unexpected side benefit. “I think when you work with nature you get all these spiraling benefits.”