|Perez Pena, J|
Submitted to: Ph D Dissertation
Publication Type: Other
Publication Acceptance Date: 12/10/2004
Publication Date: 12/21/2004
Citation: Perez Pena, J.E., Tarara, J.M. 2004. Whole-canopy photosynthesis and transpiration under regulated deficit irrigation in Vitis vinifera L. cv. Cabernet Sauvignon. Ph D Dissertation. 2004. Washington State University. 234 p. Interpretive Summary: Conventional wisdom holds that grapevines farmed under drought conditions yield better quality fruit, and hence better quality wine than those farmed under more liberally-applied irrigation. However, under drought, photosynthesis declines, and with it the sugars and other carbohydrates that are required to ripen the fruit and to be stored in the vine for weathering the cold winter and beginning growth the following spring. Without scientific knowledge of how drought or deliberately restricted irrigation affects photosynthesis, the "food" making process of the plant, it will not be possible to advise farmers and vineyard managers objectively on when and how much irrigation to apply. Market prices of grapes and wine are directly related to the quality of the fruit, which is directly related to the farmer's management of the vines, the soil, and irrigation. Thus, photosynthesis of entire grapevines was measured in a commercial wine grape vineyard that was managed with varying levels of drought by withholding irrigation to varying degrees, including the withholding of up to 2/3 of normal irrigation for a period of several weeks. Vines that were irrigated less used less water as expected, but they also had lower rates of photosynthesis, or sugar synthesis. However, the most extreme degree of irrigation withholding did not adversely affect the date of harvest, the color or ripeness of the fruit, or the perceived quality of the final product. It appears that vineyards in the inland Northwest might be able to be irrigated with less water than traditionally has been applied, without sacrificing fruit quality or marketability.
Technical Abstract: Grape growers have adopted regulated deficit irrigation (RDI) that consists of applying less water than full vine evapotranspiration (FVET)to limit water use to that amount just needed to ripen the crop, achieve the fruit characteristics demanded by winemakers, and end the season with a plant prepared for winter and the following budbreak. For better understanding of RDI on vine physiology, whole-canopy gas exchange rates were measured by a six-chamber, mobile field laboratory in 2002 and 2003. Measurements were taken at five times during the season (fruit set, pre- and post-veraison, and pre- and post-harvest) in a drip irrigated vineyard of Cabernet Sauvignon under three regimens of RDI: 1) standard deficit (replacement of 70% of FVET); 2) early deficit (replacement of 35% of FVET between fruit set and veraison); and 3) late deficit (replacement of 35% FVET between veraison and harvest). At the same time, single-leaf photosynthesis and transpiration were measured. Effects of those regimens on carbohydrate dynamics were evaluated from non-structural carbohydrates in leaf tissues and dormant canes. Vine canopies under additional water deficit fixed less carbon dioxide and transpired less than those under standard deficit. Reductions were associated with lower canopy conductance. Vines under early and late additional water deficits had lower leaf starch concentrations in the afternoon, but no differences in soluble solids concentrations. No differences were found in water use efficiency or intrinsic water use efficiency among irrigation regimens. Reductions in irrigation and water use occurred at the expense of reductions in carbon fixation. No consistent effect of additional water deficits were recorded on fruit yield or quality.