Abstract pruning systems managed during prolonged drought affect productivity, water footprint, and phenolic composition of merlot grapevine

A trial was conducted in the central San Joaquin Valley of California to quantify canopy architecture, yield components, yield efficiency, water footprint, fruit chemistry, and phenolic composition of Merlot/Freedom in response to three pruning systems and two applied water amounts. Pruning systems were cane pruned (CP) manually pruned to four, 8-node canes, spur pruned (HP) manually pruned to 22, two node spurs and mechanical box pruned (SHMP) which consisted of hedging to a 100 mm spur height. Two irrigation treatments were applied: sustained deficit irrigation (SDI) where 2.31, 1.67, and 0.39 megaliters/Ha was applied from bud-break to harvest in 2013, 2014, and 2015,respectively and regulated deficit irrigation (RDI) where 1.76, 1.25, and 0.34 megaliters/Ha was applied. Drought conditions within the experiment mitigated canopy development and yield in subsequent years. However, the SHMP system was successful in maintaining higher yields with similar quality metrics, flavonoid content, and phenolic composition as well as successfully mitigating water footprint compared to the HP and CP systems. The results from this study provides applied information to growers about successful management practices that help maintain yield and fruit composition during the transition between manual and mechanically managed vineyards under severe water deficits.