New tech saps vine water use

(NBBJ) - 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.

“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.