Regulated Deficit Irrigation for Wine Grapes – Balancing Canopy, Yield and Quality
Sebastian Braum, Ph.D., is WaterBit’s director of soil science and agronomy. He is writing a series of posts for our blog that delve into irrigation-related topics. In the piece below, he discusses deficit irrigation in wine grapes. Dr. Braum holds a doctorate in soil chemistry from the University of Wisconsin-Madison and he studied soil science, plant nutrition, agronomy and viticulture at U. of Hohenheim in Germany and Kansas State University. He has been a Certified Crop Adviser (CCA) for 20 years and a licensed California Pest Control Advisor (PCA) for 10 years. To read all of Sebastian’s “Agronomist’s Corner” posts, click here.
Regulated Deficit Irrigation for Wine Grapes – Balancing Canopy, Yield and Quality
Wine grapes are incredibly vigorous plants by nature. A cane can grow over 100 feet in length in a single season. However, winegrowers are not interested in growing long canes, which is vegetative growth. They want to direct the vines to put most of their vigor into reproductive growth–producing quality fruit for winemaking. Traditionally, growers have balanced vegetative and reproductive growth and limited the size of the canopy through pruning and removal of fruit clusters. But advances in irrigation have given winegrowers a new lever for canopy control–water.
What is Deficit Irrigation and What are Its Benefits?
In irrigated viticulture, the deliberate creation of water stress in the vines by withholding water has become the method of choice to restrict canopy growth to benefit fruit quality. This is called Regulated Deficit Irrigation (RDI). The proliferation of drip irrigation enabled the widespread use of this growing technique, as it allows for a more uniform application of water in small amounts and at more frequent intervals than was possible with flood/furrow irrigation. The vines are given less water than they would be able to use for transpiration, creating a desired level of water stress to achieve defined goals of canopy growth and fruit development. Another benefit of RDI can be water savings.
When is RDI Used in the Growing Season?
Water stressed vines early in the season are undesirable, since this would limit initial canopy growth and yield by reducing cluster count, size and reduced cell count per berry. Once berries enter the cell expansion phase, moderate water stress during pre-veraison can control vegetative growth without reducing photosynthesis of the existing canopy. From about two weeks prior to veraison until harvest, the correct level of water stress can increase sugar accumulation and fruit quality. Severe water deficit however must be avoided during this time, otherwise sugar production and accumulation is decreased, and increased berry sugar content is driven by dehydration. This creates poor quality fruit despite high sugar content. After harvest, watering should continue at a level that maintains the existing canopy until senescence, but without triggering new lateral shoot growth. Premature defoliation after harvest due to drought stress deprives the vine of the opportunity to accumulate carbohydrates for fall root growth and reserves for next season’s budbreak.
How Can Winegrowers Make Sure to Achieve the Right Level of Stress?
It is obviously not an easy task to reap the potential benefits of RDI and avoid negative results like excessive yield loss, poor quality and damage to the vines. Successful RDI requires accurate monitoring of available soil moisture, plant water status and atmospheric demand for evapotranspiration throughout the season. With that information, the correct water amount for RDI can be calculated and must then be precisely applied.
Fortunately, advances in agtech have made it easier for growers to implement RDI successfully. The WaterBit automated irrigation solution can simplify this process with soil moisture sensing and precise control of irrigation, down to small subsections of a vineyard, if desired. With WaterBit, soil moisture information and irrigation control are available 24 hours a day, wirelessly and remotely-. This allows winegrowers to make informed and actionable decisions quickly and easily.
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