Mechanical pruning in non-irrigated vineyards: effects on yield and grape composition of cultivar 'Syrah' (Vitis vinifera L.)

The effect of mechanical pruning on vine performance and wine quality was evaluated from 2012 until 2015. Two trial fields, with a randomized complete block design, were established on already existing 'Syrah' vineyards in Quinta do Côro and Quinta do Gradil, located in Tejo and Lisboa wine regions respectively. Mechanical pruning (MEC) was simulated by trimming all shoots to a 15 cm square around the cordon. Manual pruning (MAN) treatment was subjected to a traditional spur pruning. MEC tended to increase water consumption due to the higher proportion of exposed leaf area, since the total leaf area per vine was not different from MAN. The transpiration and photosynthetic rates were tendentially lower in MEC, indicating an adaptation to more stressful conditions. Yield was higher in MEC, while the individual shoot vigour and the total amount of pruning wood were lower in MEC. These results led to higher values of the Ravaz index in this treatment, reflecting changes in the partitioning of carbohydrates that were redirected from vegetative to reproductive growth. Total dry matter production (DMP) was mainly not affected by the pruning system, even in years with lower water availability. In 2014, when water was not a limitative factor, the total dry matter production was higher in MEC. The DMP in MEC was not reduced along the trial, suggesting that reserves accumulation have not been restricted. The grape composition, analyzed in 2013 and 2014, has not been significantly affected, with the exception of the total soluble solids content (TSS) and the pH, in 2014, which were lower in MEC. The results indicate that mechanical pruning is a reliable instrument to improve vine performance in non-irrigated vineyards, increasing yield without quality loss, even in dry years.