High-Tech Toast To Better Wines

High-Tech Toast To Better Wines

Pescovitz, David

California researchers map soil water content using data generated from high-frequency radar systems.

BETWEEN the rows of ripening grapes at the Robert Mondavi Vineyard in Napa Valley, a University of California (UC)-Berkeley researcher pushes a wheelbarrow outfitted with a groundpenetrating radar device. The field trip is part of a project that combines time-tested agricultural methods with high-technology geophysics to improve the quality of Northern California’s finest wines.

Yoram Rubin, UC-Berkeley professor of civil and environmental engineering, is leading research to map the soil’s water content at California vineyards using data generated from highfrequency radar systems. The aim is to give grape growers a tool for managing “stressed irrigation,” a technique that results in smaller grapes with better flavor rather than larger fruit and leafy vines.

“Our approach is noninvasive. There’s no drilling, and we can provide quick and accurate estimates of soil moisture content over large areas,” says Rubin, whose principal collaborator on the project is his former student Susan Hubbard, now a staff scientist in Lawrence Berkeley National Laboratory’s Earth Science Division. The project is part of the Institute for Environmental Science and Engineering (IESE) and the Center for Information Technology Research in the Interest of Society (CITRIS).

Currently underway at Mondavi and Dehlinger Vineyards, Rubin’s field research originated from an earlier study to monitor and understand the transport of bacteria through subsurface soil. Rubin realized that applying a similar noninvasive technique to measure distribution of water in soil could help conserve water resources in agriculture. The trick, however, was finding a receptive audience. Grape growers, he quickly realized, had a lot to gain from knowing what lies beneath the surface of their vineyards. “Managing stressed irrigation yields higher-quality fruit and enables growers to get higher prices,” he says.

Soil Diagnosis

To map the subsurface of a vineyard, Hubbard, Rubin, and his graduate students push a vacuum cleanersized radar instrument between the vines. The device sends highfrequency electromagnetic waves into the ground to depths of several meters depending on the type of soil being tested. The velocity of the waves’ reflection is dependent on the ground’s dielectric constant, the ability of a material to store electrical energy under the influence of an electric field. Soil has a low dielectric constant that is dramatically elevated in the presence of water. The signal’s travel time is then interpreted as a measurement of soil moisture.

Every vineyard’s soil will have different characteristics. At the Dehlinger vineyards, the waves bounce off a natural reflector in the ground-soil layer with significant variation in its electrical properties and return to the radar’s receiver. At Mondavi, there is no natural reflector. Instead, the instrument emits ground waves that travel laterally in a shallow zone of the soil. Depending on their frequency, the waves can penetrate up to ½ meter. The researchers take measurements and, combined with other projected data generated by a mathematical model, generate an accurate profile of the moisture around the roots of the vines.

“Once we identify the topology of the field, we can provide six or so pivot points in a block (approximately 300 meters squared) that the farmers can check biweekly,” Rubin says. “Collecting information from those points provides enough data to determine an irrigation schedule.”

Firm control over stressed irrigation, Rubin says, also enables grape farmers to create uniform ripening patterns. Rather than return to the same plot multiple times during a harvest, farmers could increase efficiency by collecting all the fruit at one time, he explains. These techniques may provide insight into the biology of the vines as well.

Rubin is currently working on a proposal to collaborate with Todd Dawson, a UC-Berkeley professor of integrative biology, on the next phase of the vineyard project. The hope is that, by combining the soil moisture profiles with Dawson’s isotope analysis, a method used to determine distribution of elements, the researchers will be able to produce a picture of how the vines drink from the soil.

David Pescovitz is currently the writer-in-residence at University of California-Berkeley’s College of Engineering. This article originally appeared in the college’s online publication, “Lab Notes.” E-mail questions or comments about this article to wfg.edit@meistermedia.com.

Copyright Meister Publishing Company May 2004

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