The effects of irrigation on the water relations of the grapevine, yield, grape and wine composition of Tempranillo cv in Mediterranean climate

The main goal of this study was to evaluate the behaviour of Tempranillo variety when a drip irrigation was applied to a vineyard in a Mediterranean area. The vineyard was located at the experimental field of the Faculty of Enology (University of Tarragona). The trellis system was a vertical shoot positioning with a bilateral cordon pruned. Plant density was 3 000 plants per ha. The split-plot design was established with 3 repetitions for the irrigated plot and non irrigated one. Each elemental plot had 24 grapevines, 72 plants in total per treatment. The irrigation was defined with water amounts of 35%of ETo in 1998 and 70%of ETo in 1999 (ETo: evapotranspiration of the reference). The ETo were calculated by Penman. Transpiration was measured using a sap flow meter using 3 probes for irrigated and 3 for non irrigated grapevines. Several plant growth parameters: the length of the shoots, leaf area, the yield, the pruning weight and the analyses of the Point Quadrat, were evaluated on 12 plants as replicated. Leaf water potential was measured by Scholander chamber. Microvinifications were carried out in 100L tanks and chemical analyses of the wines were done during two years. Chemical analyses of wine: alcohol degree, total acidity, pH, the level of anthocyanin and tanins, the total phenol content (IPT), and the colour intensity (IC) were determined on the obtained wines. By statistic analysis, it was confirmed that irrigation produced an increase of plant transpiration, growth and vigour, but not a significant increase of production. The predawn leaf water potential have shown similar values between treatments at véraison (-0.4 to -0.55 MPa in August). There were no difference between treatments on wine analyses (alcohol degree, total acidity, anthocyanin, IPT, and IC), however, significant differences were found through the vintage effect. The spring of 1999 was more rainy comparing to the 1998 and due to the particular mesoclimate, a big increase of yield was registered. It could be a reason for a decrease of wine quality in 1999: less alcohol degree and weak colour in comparison with 1998 wines. After analysing the results obtained during two years, the study revealed the great importance of the year (millésime) in most of the parameters analysed and the important role of the soil as a good reservoir of water.