TY - JOUR T1 - High Planting Density Reduces Productivity and Quality of Mechanized Concord Juice Grapes JF - American Journal of Enology and Viticulture JO - Am J Enol Vitic. DO - 10.5344/ajev.2021.21014 SP - ajev.2021.21014 AU - Markus Keller AU - Lynn J. Mills Y1 - 2021/08/19 UR - http://www.ajevonline.org/content/early/2021/08/18/ajev.2021.21014.abstract N2 - The choice of planting density is a key decision with long-term implications for grape growers to make before vineyard establishment. The field trial with drip-irrigated, machine-pruned Concord juice grapes described here tested the effects on yield formation and fruit composition of two between-row distances (2.44 m and 2.74 m) and four within-row distances (0.91 m, 1.83 m, 2.74 m, and 3.66 m), resulting in planting densities ranging from 997 to 4485 vines/ha. Canopy size, yield components, and fruit composition were measured over 6 years, starting in year 3 after planting. Whereas in the first cropping season the yield at 0.91 m and 1.83 m vine spacing (11.8 t/ha) was twice that at 2.74 m and 3.66 m (5.6 t/ha), on average over the 5 subsequent years the yield of 0.91-m vines was 38% lower (18.2 t/ha) than that at the other planting distances (29.2 t/ha). During the last 4 years, the average yield of vines planted at 2.44 m between rows was 2 t/ha higher than that at 2.74 m. The yield potential and fruit quality of closely spaced vines (0.91 m) was compromised by their vigorous growth, high canopy density, and poor microclimate, which resulted in fewer clusters/vine, fewer berries/cluster, lower cluster weights, and more bunch-stem necrosis. Leaf death in the canopy interior was associated with nutrient remobilization and high potassium and pH in the juice from 0.91-m vines. Juice total soluble solids, titratable acidity, and color remained unaffected by planting density. These results show that planting juice grapes at high density in irrigated and highly mechanized vineyards is detrimental to both cropping potential and fruit quality. ER -