Trellis Conversion Comparison of Crop Load Management & Regulated Deficit Irrigation
A traditionally managed head-trained, cane-pruned Merlot/Freedom vineyard planted on a California sprawl trellis was converted either to a bi-lateral cordon spur pruned (HP) or single high-wire bi-lateral cordon mechanically pruned (SHMP) crop load management system beginning in 2014. Two irrigation treatments were applied. Vineyard was irrigated as follows A control treatment of sustained deficit irrigation (SDI) at 0.8 of estimated ETc was applied from anthesis until harvest (EL Stage 38) with a mid-day leaf water potential (?l) threshold of -1.2 MPa. A regulated deficit irrigation (RDI) treatment was applied at 0.8 ETc from anthesis to fruit set (EL Stage 28) with a ?l threshold of -1.2 MPa, 0.5 ETc from fruit set to veraison (EL stage 35) with a ?l threshold of -1.4 MPa and at 0.8 ETc from veraison until harvest with a ?l at -1.2 MPa. Irrigation treatments were not initiated until ?l reached -1.0MPa for vines in the 0.8 ETc treatments. It took one season to convert and establish canopies that can be cropped. The SHMP treatment irrigated with the SDI irrigation method generated the largest canopy earlier and was the most efficient user of applied water to fix carbohydrates. Furthermore, this canopy also yielded the greatest with acceptable canopy architecture and microclimate variables for the warm climate. There were few statistically significant effects of crop load management treatments or irrigation methods applied on skin flavonoids. The total berry skin anthocyanins were most affected by the HP and SDI treatments in the initial year of data collection, but in the second year of data collection SHMP, irrigated with SDI had the greatest total skin anthocyanin accumulation. The preliminary results suggest that it would take one full growing season to convert traditional California sprawl canopies to a SHMP trellis. The resultant canopy is a more efficient user of applied water amounts to fix carbon with greater yields with similar berry skin phenolics. The study is providing important science-based information for California wine grape growers on how best to manage traditional vineyards in times declining resources such as labor and water.