Grapevine (Vitis vinifera) yield and quality response to irrigation

In a sub-humid area, like the Emilia Romagna region, the irrigation of grapevine was often considered as an exceptional practice that was only necessary in very dry years. Moreover, the grapevine water supply was associated with the risk of losses in terms of must quality, especially for what concerned the degrees Brix and the acidity. The aim of the trial, carried out from 1987 to 1992 on Trebbiano grafted on SO4, was to identify the most suitable irrigation regime in order to reach an high must quality level without a great increase of the yield. The irrigation regimes compared were as follows: rainfed; 50%, 100% and 150% of ETc. As a result of the water supply, the production in the first three years was higher than the rainfed (+23%), with relevant economic effects. This yield increase was related to the reduced competition between the vegetative and the reproductive sink in the first stages of the vineyard life. The average yield increase due to the irrigation during the six years of trial was about 14%, thus not so relevant. No significant differences were observed among the ETc replenishment. The quality characteristics were the same in the rainfed as well as in the irrigated thesis, e.g. the average degrees Brix variation in the irrigated thesis was equal to +0.25, once more without differences among ETc replenishment.