Optimizing Irrigation for Mechanized Concord Juice Grape Production

Background and Goals Economic considerations and water shortages associated with climate change are driving the conversion of many hand-pruned and furrow- or sprinkler-irrigated juice grape vineyards in arid eastern Washington to mechanical pruning and drip irrigation. However, juice grape producers have traditionally avoided plant water deficits, fearing a decline in vineyard productivity.

Methods and Key Findings We conducted a 6-year field trial to test the impact of eight drip-irrigation treatments on large, mechanically-pruned Concord grapes. We found an estimated crop coefficient of 1.05 between fruit set and harvest. Replacing 75% of crop evapotranspiration (ET_c) from fruit set through harvest reduced annual irrigation water supply by 20% compared with the 100% ET_c control without altering canopy size, yield, and juice composition. Decreasing the water supply from 100% to 50% ET_c at veraison saved only 8% irrigation water, while irrigating at 50% ET_c from fruit set through veraison and 100% ET_c thereafter reduced irrigation water use by 30% but decreased canopy size and reduced yield by 14%. Replacing 150% of ET_c between fruit set and veraison increased seasonal water use by 20% but did not alter yield or juice composition.

Conclusions and Significance Deficit irrigation does not impact crop yield and juice composition, so long as vines experience only mild water stress (midday stem water potential > −1 MPa) before veraison. Irrigating at 75% ET_c to impose mild preveraison water stress and mild to moderate postveraison stress optimally balances the goals of water conservation and yield and quality sustainability in juice grape production.