Is Pre-Veraison Irrigation Cut-Off more Convenient than Post-Veraison Water Stress as a Strategy to Improve Grape Composition in Vitis vinifera 'Tempranillo' in Spain?
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Irrigation of grapevines to meet the full seasonal water needs (ETc) usually negatively affects wine composition. In addition, our previous results showed that under Mediterranean climate replacing approximately 50% of full ETc ensures a substantial yield increase, compared with rain-fed conditions, with no detrimental effects on grape composition. The question then is whether it would be better to concentrate the water applications during the pre-veraison or during the postveraison period. A field experiment was carried out in a 'Tempranillo' vineyard during 2007 and 2008 where different irrigation strategies were applied at two crop levels (Normal and High). Rain-fed (NI) vines were compared with vines that were constantly irrigated at 75% of ETc (Control). Irrigation to the Control commenced when midday stem water potential (Psi(stem)) values reached -0.7 MPa. In addition, a spring water shortage strategy (ED) was applied by withholding irrigation until. stem Psi(stem) surpassed -1.0 MPa. After that, 75% of ETc was applied. Finally, a LD treatment was irrigated as per the Control up to veraison, and thereafter water application was reduced to approximately 2550% of ETc, trying to avoid. stem surpass -1.4 MPa. Results indicated that all irrigation regimes increased vine yield up to 50% with respect to the NI and no differences in yield among the irrigated treatments occurred. However, there were large differences in berry composition among the different irrigation strategies. The ED was more effective than LD in reducing berry growth leading to more concentrated berries in terms of anthocyanins. The LD impaired berry sugar accumulation due to the detrimental effect of water stress on leaf photosynthetic rate. Thus, in our conditions of scarce water resources, applying moderate water deficits before veraison and irrigating without considerable restriction afterwards, appears as the most convenient irrigation strategy. Crop level did not affect grape composition.