By Tracey L. Kelley
Galileo said, “Wine is sunlight, held together by water.” A wine enthusiast may have this quote in calligraphy on a decorative wall hanging, but winemakers and vineyard managers know the truth behind it.
Vineyard irrigation isn’t often a romantic craft topic, but its constant evolution requires frequent examination and an exchange of knowledge so each droplet replenishes the vine in just the right way. And while American Viticultural Areas (AVA) delineate regions with similar characteristics, individual landscapes still present unique challenges in water management that encourage or prohibit the best yield. This is when the application of science influences art.
Fine-Tuning Your Approach
Maybe after last year’s harvest, you discovered some inconsistencies. Perhaps your current system isn’t as effective, or needs other modifications. Or as the acreage grows, it’s harder to keep up with soil variations and water needs in certain areas. “Irrigation management takes a lot of time and effort to ensure it’s managed correctly,” said Wesley Porter, assistant professor and extension precision ag and irrigation specialist with the University of Georgia (UGA). “Precision irrigation is critical to proper crop production and quality. This allows for more stabilized yields during times of low to no rainfall, more commonly known as periods of episodic drought. So this is a task growers should take seriously.”
Technological applications in precision viticulture continue to expand the potential of using quality data and devices with which to base decisions. For example, aerial mapping by drone enhances topographical views. Remote sensing, first established for many aspects of agriculture the 1960s, is now an essential component of vineyard irrigation systems. “Using only sight inspection to determine irrigation scheduling isn’t the most valid method, as once moisture stress is visible, typically yield is lost,” Porter told The Grapevine Magazine. “More advanced methods should be implemented such as soil/water balance models or soil moisture sensors to make appropriate irrigation scheduling decisions.”
Usually there are two ways to measure soil moisture in an active vineyard:
- Tensiometric measurement, or soil water tension, which analyzes the physical force holding water in the soil.
- Volumetric measurement, which evaluates the percentage of water in a certain area of soil.
Often, it’s important to understand how difficult it is for vines to draw water from the soil. Soil texture classes for vineyards include clay, loam, sand, and silt, with varying characteristics for each. Many growers often deal with a combination of soil compositions in their landscapes, and this means continuing to recalibrate irrigation procedures with proper data.
Tom Penning is president of IRROMETER, based in California. The company manufactured the first commercially-viable tensiometer for use with scheduled irrigation, and now has a product line that includes sensors, reading meters, and remote data access portals. Penning said these technological field tools help producers strategize irrigation needs and solve problems, such as excessive run-off or pooling, more quickly.
“The sensor data gives them information on water availability with which to make these decisions. If evidence of significant variability in percolation is revealed, then the grower can determine where to change emitter sizing to better match the soil characteristics,” he said. “Sensor data provides better resolution of where and when these problems occur, thus allowing the grower to better address the issues.”
IRROMETER’s tensiometric devices don’t require site calibration, but volumetric measurement devices often do. Since most soil moisture sensors work with a variety of irrigation methods—including drip, sprinkler and micro-spray—a producer’s choice often relates to irrigation capabilities, terrain and personal preference.
And a winemaker’s approach to irrigation refinements and scheduling might include a solid combination of tech along with paying attention to the vine’s subtle hints.
“I like to make a ‘leaf sandwich’—gauging leaf temperature by holding a leaf between your hands,” said Gill Giese, a viticulture extension specialist at New Mexico State University. “Even a fully-exposed leaf should be somewhat cool to the touch. If not, the vine may be stressed. Other vine-based indicators are drooping leaves, such as when you see their angles in relation to the sun are bent downward to avoid full exposure. Finally, look at the tendrils. If they’re exerted beyond the shoot tip, then the vine is likely not water stressed,” Giese said.
A longtime educator, Giese is also a former winegrower for Shelton Vineyards in the Yadkin Valley region of North Carolina—the first AVA recognized by the U.S. federal government. One challenge there had less to do with designing an effective watering system, but rather dealing with the excess moisture of the region due to humidity and rainfall—a common problem for many growers east of the Rocky Mountains. He advised producers to assess other site-specific factors when determining irrigation needs.
“All the vine-centric parameters should be considered: climate, vine spacing, trellis type, variety and rootstock, training system and production goals—both quality and quantity. These needs are reevaluated as the vineyard develops and grows, year-to-year and within a given season. Vine age and phenological growth stage impact the optimum water requirements as well,” Giese told The Grapevine Magazine. “Additionally, beyond the obvious differences of climate during the growing season such as differences in precipitation and vapor pressure deficit, grapevines progress through the same growth stage, regardless of location. The optimum amount of water for each growth stage must be learned at each location.”
Penning said one problem growers face is they often don’t know the variabilities that exist within the soil in the vineyard. “The use of soil moisture sensors illustrates the status within the root zone, which isn’t visible without in-situ instrumentation,” he said. “The status below ground as well as what’s visible on the surface at representative locations provides the grower with comprehensive data when they schedule irrigation.”
A frequent question about irrigation practices involves understanding when not to water. This harkens back to the adage of “stressing the vine.” Giese had thoughts about this.
“The grapevine needs a slight water deficit just after berry set in order to limit berry size at veraison and harvest. Regardless of location, a widespread belief or practice is limit water to vines post-veraison. This is tricky,” he said. “Too much stress and the leaves stop photosynthesis. If this happens, the flow of sugar and other assimilates is halted and berry-ripening suffers. If photosynthesis stops and then water is supplied, the delay in reactivation of photosynthesis may too late to be optimal. But growers east of the Rocky Mountains differ because of water excess due to rain post-veraison. In some dry vintages, they’re tempted to totally withhold water post-veraison, and this can be a mistake.”
Giese suggested producers apply stress through regulated deficit irrigation, but don’t over-stress vines. The University of California, Davis (UCDavis) Drought Management Department provides detailed information about this practice on its website. For further reading, also consider Pete Jacoby’s research at Washington State University about deeper subsurface irrigation systems that force grapevines to extend root zones, stress plants only slightly, and require less irrigation.
Finally, if you’re not already employing the use of cover crops between the rows to boost irrigation efforts, these experts encouraged you to do so.
“The correct selection of cover crops help in many ways,” Porter from UGA said. “They aid in shading the soil surface and improving soil structure, both of which reduce evapotranspiration; and also aid in increasing infiltration and reducing runoff. Cover crops also encourage weed suppression.”
Giese added, “Cover crops can provide competition for excess nutrients and water in the case of regions with excess rainfall. They also provide numerous other benefits: ground cover or thatch/mulch that limits evaporation, increased infiltration rate of water, better soil structure and thus, improved water holding capacity, increased organic matter, mitigation of erosion and others,” he said. “But in the Southwest, most growers don’t employ cover crops, as the amount and cost of additional water required is prohibitive. I currently have some studies in place to take critical look at some ground cover options in the Southwest.”
Right Now, It’s All About Maintenance
The average cost of a vineyard drip or micro-sprinkler irrigation system ranges $1,500-$3,000 per acre. While some growers may participate in a cost-sharing plan, managing this investment effectively comes down to maintenance. Here are a few things to consider.
- Growers west of the Rocky Mountains might still need to water once a month or so “to ensure the soil profile is nearly full when vines are ready to bud out in spring,” said Giese.
- Growers east of the Rockies should winterize their systems. “Check for leaks, evaluate hose structure, check the pumping system and filters and so on,” said Porter. He offers a number of irrigation resources, including checklists for maintenance, on the UGA Extension website.
- Throughout North America, wildlife control is an ongoing concern in irrigation maintenance. “This is a hard issue to resolve,” Porter said. “Do the best job you can to keep equipment protected either in weatherproof enclosures or critter-proof sheathing. Ensure that drip tape and emitters are buried and/or out of their reach.”
- Get started on growth season maintenance by clearing vines, roots and weeds from emitters, testing soil and water, calibrating pressure gauges to manufacturer guidelines and running pump tests.
- Also use this time to look into more cost-savings measures. For example, solar-powered drip irrigation systems help growers better manage energy and water consumption. A fact sheet is available on the UCDavis website.
Incorporate Conservation Methods Now
A primary concern of any vineyard owner is proper land management, and water continues to be a critical resource to conserve. “Global water concerns heighten the awareness of the importance of water use efficiency,” Penning said. “Precision agriculture includes exact water management, and these concepts are needed for sustainability of the resource.”
World climate data indicates the past four years were the hottest on record, with expanded drought events. While grapevines endure heat and drought better than most crops, and dry farming is still popular throughout Europe, growers notice climate changes and the need to modifying practices. In 2018, excessive drought in South Africa’s Western Cape reduced harvest by 15 percent. Producers there are evaluating drought-resistant vines still rich in flavor, intensity and acidity. Growers in France are purchasing land farther northwest in chilly, cloudy Brittany, once considered undesirable because of winds and moisture off the Atlantic Ocean.
In America, the Petaluma Gap in Northern California received an AVA designation in December 2017—something that probably wouldn’t have happened 20–30 years ago for this cooler, slightly wetter clime. Similarly, the Van Duzer Corridor in Oregon is experiencing rapid growth as winemakers use the region’s hot, dry days tempered by cool nights and damp morning fog to nurture thin-skinned grapes.
Giese said proper water and irrigation management has always been critical to growing wine, and will continue to become more of an issue as increased demands are placed on water supply. “Growers in the West have been aware of this for some time. Look to work being done in California and Australia for trends in irrigation and management. Often growers of other high-volume or high-value crops use techniques we can adopt for advantage in winegrowing,” he said.
One rising trend in North America is the use of vineyard waterbodies for irrigation needs. Few vineyards have quality wells to draw from, and many states and provinces continue to implement strict water rights and usage laws for agricultural access to springs, running water sources and municipal or rural systems. Depending on the size of the property, even a two- to three-acre pond can be a viable, independent source of summer irrigation.
A strong sustainable method for drip irrigation systems, ponds can also flash supply micro-sprinkler applications when vines are in need of frost protection or conversely, cooling from high heat, without too much danger of exhausting the pond when more frequent irrigation scheduling events are necessary. Primary reservoirs are often reliant on rainfall as well as subsurface water collection drains for replenishment, but additional waterbodies can be created to contain and later aerate wastewater from the winemaking process.
There are some concerns when sourcing from onsite still water sources. Following local and federal quality regulations and frequent testing for algae, nuisance weeds, invasive species, bacteria and chemical runoff from neighboring farms are major management issues. Pest and mosquito control can sometimes be a problem. Wildlife in search of fresh water can damage or pollute a reservoir, or happen to also love juicy grapes, furthering labor efforts for netting and other protective methods.
There’s also the investment. For example, if there isn’t a suitable clay soil site on a property to use as a base, then installing additional soil reinforcement or even liners is necessary. Proper buffering methods are a must as well. On average, the cost for vineyard pond construction could escalate beyond $200,000. However, the need for conservation is so great, there may be options.
“Often, government agencies incentivize the purchase of such irrigation water management tools to improve the efficiency of water use,” Penning said. “Growers should check with their local agencies to see if funding is available to help subsidize the investment.”
In addition to county and state initiatives supporting soil and water conservation grants, another possibility to establish a sustainable irrigation system is the USDA’s Natural Resource Conservation Service. The agency often extends funding through its Conservation Stewardship Program, Environmental Quality Incentives Program, Regional Conservation Partnership Program and water-based Landscape Conservation Initiatives.