regulated deficit irrigation – part i « lodi growers · 2015-05-12 · regulated deﬁcit...

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Coffee ShopRegulated Deficit Irrigation – Part I

Deficit irrigation refers to the practice of applying less than the fullamount of water a vineyard can use. The objective of deficit irrigation is to induce and sustainmoderate water stress that arrests shoot growth and limits fruit growth without impacting foliage

Regulated Deficit Irrigation – Part I « Lodi Growers http://www.lodigrowers.com/regulated-deficit-irrigation-part-i/

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health and sugar accumulation. This is possible because shoot growth and berry growth are moresensitive to water stress than sugar accumulation. Deficit irrigation reduces irrigation costs and bunchrot, but also improves fruit quality through increased fruit acidity, lowered pH, and increasedphenolics (color, aroma, flavor, and astringency). Many wineries promote deficit irrigation becausethe fruit quality benefits translate into higher quality wines that effectively compete in the winemarket.

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This is the first of a two part series on regulated deficit irrigation by Stan Grant.Part II will be posted on August 4th.

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Figure. 1. Complete canopy development witharrested shoot growth. Photo: ProgressiveViticulture©

Successful deficit irrigation has a few requirements. First, effective deficit irrigation requiressustained moderate water stress while avoiding severe water stress, which is detrimental to fruitquality and vine health. The Australians who pioneered the technique refer to it is as regulated deficitirrigation (RDI) to emphasize the importance of regulating the water stress with the moderate range.

Successful RDI also requires that early in the season, prior to imposing water stress, vines have accessto sufficient soil moisture to produce fully developed canopies (14 to 20 nodes per shoot)(fig 1). Inaddition, it requires that after harvest until the first frost, vines have access to sufficient soil moistureto relieve stress and maintain healthy leaves, which is critical for producing and storing carbohydratesfor use early in the next growing season. Therefore, a sustainable RDI strategy involves minimumwater stress prior to fruit set, moderate water stress from fruit set to harvest, and minimum waterstress following harvest.

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A version of this article was originally published in the Mid Valley AgriculturalServices’ May 2002 newsletter.

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Normally, no early season irrigations are required to grow full canopies in vineyards with small vinesor low vine densities and soils with large moisture holding capacities. In contrast, vineyards withlarge vines or high vine densities and soils with low moisture holding capacities often will not reachfull canopies without early season irrigations. For example, early season irrigations are rarelynecessary for small head trained vines on deep Tokay sand loam near Lodi, but they are common forquadrilateral trained vines on Redding gravelly loam in the Clements area. The need for early seasonirrigations can be determined from vine appearance, pressure bomb readings, or soil moisturemeasurements.

Figure 2: The vineyard moisture continuum. Image:Progressive Viticulture©

During the growing season, successful RDI implementation requires monitoring of the moisturecontinuum that extends from the soil either directly to the atmosphere or through the vines to theatmosphere (fig 2). Of course, within the continuum our primary focus is the vines. Their conditionand appearance at any particular time during the growing season relative to the state we expect orwant is the primary consideration for our irrigation scheduling decisions.


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Figure 3: Apical end of shoot whose growth isarrested. Photo: Progressive Viticulture©

Early in the season shoots should have a moderate growth rate and leaves should be normal in size. After reaching full canopy, suspend irrigations or continue to withhold them to arrest shoot growth,which is evident in pale shoot tips, short internodes near the tips, obscuring of the shoot tip by apicalleaves, and possibly, slight tendril and petiole wilting during the warmest part of the day (fig 3).

Once shoot growth has been arrested, RDI is practiced to sustain foliage without renewed shootgrowth (fig 4). Basal leaf yellowing or scorching indicate severe water stress and the need forincreased irrigation. Before such leaf damage is readily apparent, leaves may appear slightly wiltedand exposed leaf tissues may be warm and appear faded.

Development of full canopies, arresting of shoot growth, and imposition of moderate water stressshould occur shortly after bloom to achieve the maximum fruit quality benefits from RDI. Latertimings will still render beneficial effects, but they are somewhat diminished.

In the next posting, we will discuss the other components of the soil-vine-atmosphere continuum andirrigation scheduling after shoot growth has been arrested.


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Figure 4: Mid season healthy grapevine foliagemaintained under moderate water stress. Photo:Progressive Viticulture©

Further Reading

Goldhammer, DA; Snyder, RL. Irrigation scheduling: a guide for efficient on-farm watermanagement. University of California, Division of Agriculture and Natural ResourcesPublication 21454. 1989.Grant, S. Five-step irrigation schedule: promoting fruit quality and vine health. PracticalWinery and Vineyard. 21(1): 46-52 and 75. May/June 2000.Hanson, B; Orloff, S; Sanden, B. Monitoring soil moisture for irrigation water management. University of California Agriculture and Natural Resources Publication 21635. 2007.Hardie, W. J., and J. A. Considine. Response of grapes to water-deficit stress in particularstages of development. American Journal of Enology and Viticulture. 27, 55-61. 1976.Matthews, M. A., R. Ishii, M. M. Anderson, and M. O’Mahony. Dependence of wine sensoryattributes on vine water status. J. Sci. Food Agric. 51: 321-335 (1990).Matthews, M. A., and M. M. Anderson. Fruit ripening in Vitis vinifera L.: responses toseasonal water deficits. American Journal of Enology and Viticulture. 39, 313-320. 1988.Matthews, M. A. and M. M. Anderson. Reproductive development in grape (Vitis vinifera L.):responses to seasonal water deficit. American Journal of Enology and Viticulture. 40: 52-60. 1989.Prichard, TL; Hanson B; Schwankl, L; Verdegaal, P; Smith, R. Deficit irrigation of qualitywinegrapes using micro-irrigation techniques. University of California Cooperative Extension,Department of Land, Air, Water Resources, University of California, Davis. 2004.Prichard, T; Storm, CP; Ohmart, CP. Chapter 5, Water Management. In: Lodi Winegrower’sWorkbook, 2nd Ed. Ohmart, CP, Storm, CP, Matthiasson, SK (Eds.). Lodi WinegrapeCommission. pp. 142-186. 2008.Schwankl, L; Hanson, B; Prichard, T. Micro-irrigation of trees and vines: a handbook for watermanagers. University of California Irrigation Program, University of California, Davis. 1995.

© Progressive Viticulture

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regulated deficit irrigation – part i « lodi growers · 2015-05-12 · regulated deﬁcit...

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