Optimizing Irrigation for Mechanized Concord Juice Grape Production

Abstract

<h3>Background and goals</h3> 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. <h3>Methods and key findings</h3> We conducted a six-year field trial to test the impact of eight drip-irrigation treatments on large, mechanically-pruned Concord grapevines. 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% below that of the 100% ET_c control without altering canopy size, yield, or 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. <h3>Conclusions and significance</h3> Deficit irrigation does not impact crop yield and juice composition, so long as vines experience only mild water stress (midday stem water potential &gt; −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.