Grapes and Water-Use Efficiency
Symposium at ASEV meeting addresses how to make the most of water
Wine grapes require less water to mature than some other crops, and often rainfall can provide much of the required water. However, when water of marginal quality is used for irrigation, the level of soil salinity can increase, according to Donald L. Suarez, laboratory director at the USDA Agriculture Research Service Salinity Lab in Riverside, Calif. As a result of the changes in salinity, it may be necessary to alter water-management practices, and possibly include leaching to control the level of salinity.
Suarez presented a study designed to evaluate the effectiveness of leaching to control root-zone salinity by drip or sprinkler irrigation at three sites. He found that there was a “winter irrigation window” when the plants were dormant and the soil was wet, and leaching at that time had a “major impact on spring salinity levels, even in years of average to low rainfall.” Drip irrigation was more effective on heavier soils and sprinklers on sandy soils.
Research from Australia
Michael McCarthy, principal viticulture scientist at the South Australian Research & Development Institute in Nuriootpa, South Australia, discussed the use of reclaimed water as a response to the need for additional water supply when none other existed. Beginning in the 1960s, reclaimed domestic wastewater from Adelaide has been sent to a large commercial vineyard in response to restrictions regarding use of underground water. In the 1990s a privately owned pipeline was constructed from Adelaide with a highly flexible pumping capacity. Now, with frequent drought conditions in Australia, there is increased interest in reclaiming winery wastewater as well.
There are numerous issues with using reclaimed water from domestic sources, including salinity levels, nutrient content and health issues. However, the quality of that water has been relatively consistent. Winery wastewater brings concerns of salinity, potassium and pH levels as well as the variability in the total chemical make-up of the water. McCarthy stated that all reclaimed water is different, and that monitoring protocols must reflect those differences in sources. Long-term changes in the soil must be quantified, and soil, plants, berries and wine must be monitored. Most important, the wine industry must demonstrate the long-term sustainability of the use of reclaimed water and present it as a positive image: that the wine industry is doing the right thing by reusing water that traditionally would have been dumped in the ocean.
Plants (including grapevines) have a minimum amount of water they need in order to survive, and various grape cultivars require different amounts of water. Mark Greenspan of Advanced Viticulture in Windsor, Calif., looked at adapting technology toward efficient vineyard water management. According to Greenspan, irrigation should be initiated as late as possible and should be scheduled based on soil moisture. Only as much water as is needed should be applied—and only when it is needed. It is most important to determine the plant’s water status so that the irrigation schedule intervals can be appropriately adjusted.
The first assessment should be of the visual indicators of the plant’s water status. Are the shoots growing rapidly? Have they slowed in their growth or stopped growing? Are the shoot tips dead? In addition, various technological tools can be employed to test the plant’s water status. A pressure bomb, which is a pressured chamber device, can measure the “suction” in the xylem; a porometer can measure the stomatal conductance (the facility of pores to transpire water). While these measurements of the plant aboveground are important, it’s also necessary to determine the soil moisture profile.
Greenspan determined that a soil water content probe should be placed between 1 inch and 4 inches from the drip of the emitter (and not directly under the emitter), as where the probe is placed influences the data recorded. Feedback of the relative water content at different depths can be plotted, and the shape of the resulting curve shows when the water is being absorbed. According to Greenspan, “It’s a matter of getting the vines stressed and using the probe to determine the irrigation level, and it’s less than you might think.”
In the news
A panel discussion about the political and regulatory issues raised by declining water resources and competing demands for water concluded the seminar. Michael Schwisow, a lobbyist for the Washington State Water Resources Association and the Washington Association of Wine Grape Growers; Kurt Schwabe from the University of California, Riverside; Jason Peltier, representing the Westlands Water District in California’s Sacramento Delta, and Doug Caroom of Bickerstaff Heath Delgado Acosta LLP in Texas brought different perspectives to the political and policy issues of water use efficiency.
After more than an hour’s discussion, it was apparent that there are no easy solutions to the questions of water use, water rights and how water should be managed in the future. Each aquifer is different: Some may be able to be recharged, others may just be depleted. The aquifers aren’t local, and they don’t follow political lines. Consequently, determining which government entity can or should set water regulations is problematic. The stresses between agricultural areas versus urban regions, and old development versus new development, create a situation where any actions will probably be met by people who object to any change.
Water-use efficiency is a complicated topic. The symposium began a dialogue about many of the variables and the issues, and it presented a great deal of information about current knowledge concerning water use at many levels. However, the ultimate solutions will require more study, more discussion and greater understanding not only in the wine industry, but also in the agricultural community and across society in general. At this time, the best solutions remain elusive.