Vineyard Water Management During a Drought (Excerpts)

Rain or shine, we're under drought conditions - be good stewards of a precious resource.

By Mark Greenspan. (Source Article)

Quantification of water relations is key. That means we need to measure things. I’ve been a big fan of plant water status measurements, and you can refer to my previous articles on irrigation for deeper descriptions. The two pieces of plant moisture equipment that I rely on most are the pressure chamber and the porometer. I’ve described both in previous articles, but both are portable instruments that we use primarily during midday to measure plant water status. I find both tools to be indispensable. I only wish there were ways to make those measurements automatically because the short afternoon window, travel time and expense make extensive measurements with those instruments difficult and costly. I am looking at other options for these measurements; but until then, we are getting our money’s worth out of them. Knowing the water stress level of the vine allows us to modify our irrigation regime to dial in specific stress levels in the vines at certain times of the growing season and avoid going overboard with stress, potentially causing crop loss or quality reduction.

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Soil moisture monitoring has also allowed me to reduce the irrigation quantities applied once irrigation cycles begin. By monitoring the total amount of moisture being stored in the soil from an irrigation and then depleted by the vine, I almost always apply between 18 to 22 percent of crop evapotranspiration (Etc) as a maintenance (non-deficit) level. That is far less than is being applied by many growers, who believe that they are “deficit” irrigating at 50 to 60 percent of ETc. I believe the issue with the ETc model, in general, is that it does not account for stomatal pore closure, which occurs in the vines as the season progresses, even without water stress, but is greater (i.e., more closed) under desirable levels of water stress for fine winegrapes. Because I’ve discussed these measurements before and have not changed my practices, I will not go into their use further in this column but rather discuss general practices under drought conditions.

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Drought Management Practices
There are many other practices that should be applied during periods of drought. Here is a brief list:

• Eliminate competition by disking cover crop and controlling weeds. I normally encourage no-till or minimal tillage; but if water is scarce, save it for the vines by getting rid of the other foliage.
  
• Keep canopies small (I already said that, but it’s important) by discouraging excessive moisture during canopy development. Sucker and shoot-thin early and aggressively to remove wasteful water “straws.”
  
• Reduce irrigation during post-set to veraison. This will create smaller berries and will also improve phenolic development during ripening. You can increase the water status of the vines after all fruit has gone though veraison.
  
• Reduce crop level. Fruit will be a factor after veraison so make sure that you remove your excess crop before veraison, and you may need to drop more than usual, depending upon the water conditions later this season.
  
• Check vine nutrition. All nutrients that enter through the root system use water as a carrier. Nutrition will be lower when soils are dry. Check potassium status especially, as potassium helps the vines to regulate their stomatal pores.
  
• The “small drink” will use less water than the “big drink.” More to follow.
  

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To me and my certified crop advisor colleagues, irrigating deeper than the root system is a no-no. It not only pushes water past the root zone, where it cannot be taken up, but it also moves nitrate and other potential pollutants (think persistent and mobile pesticides) past the root zone and into the vadose zone (the zone between the root system and the water table). The soluble materials and water are either lost, or they move into the groundwater or in surface or subsurface run-off, all of which will occur in wetter climates.

TO READ THE ENTIRE ARTICLE, VISIT WINE BUSINESS MONTHLY.

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