Abstract
Climate change is associated with changing temperature and precipitation regimes, particularly pronounced in the Alpine areas. The expected greater inter-annual variability is going to affect grapevine growing performances. This study aimed to assess the effect of different water supply management strategies on grape production in two growing seasons characterized by very different meteorological conditions. The trial was carried out with Sauvignon Blanc (on SO4 rootstocks) grapevines grown on a sandy and shallow soil in a hilly area close to Bozen-Bolzano (South Tyrol, Italy). The manipulative experiment consisted in three water volumes regimes: a) Full irrigation FI (around 66% of ET0), b) deficit irrigation (DI=50% of FI) and c) no irrigation, rain fed vines (RF). The growing season 2014 showed a short drought period during the early phase of berry growth followed by an atypically high precipitation regime afterwards. Differently, in 2015 a similar water stress in June was followed by another severe drought period at the end of July. The predawn leaf water potential in RF plants under stress conditions reached minimum values of -0.7 MPa in 2014 and -0.9 MPa in 2015. DI and RF treatments led to a significant yield reduction in both years as compared to FI, which was especially pronounced in 2015 (-53 % for DI and –76% for RF) due to the prolonged water stress period. RF always showed higher sugar content of berries at harvest as compared to FI: berries from DI had similar sugar content as those from FI in 2014 and similar to those from RF in 2015. No irrigation (RF) reduced the vegetative growth, assessed by the amount of pruning wood, in 2015 only. Our results indicate that the effects of water stress on grapevine performances depend on the intensity and the period of the season it occurs. Development of irrigation strategies based on objective drought stress indicators, are needed to allow optimal soil moisture regimes under variable seasonal climatic conditions.