Long-term effects of tree density and tree shape on apple orchard performance, a 20 year study-Part 1, agronomic analysis

While the adoption of high-density apple orchards during the last decades has resulted in a significant improvement in yield and fruit quality, there is great disparity of opinion on the optimum density or the optimum tree shape. A 2-ha replicated field trial was planted in 1997 at the New York State Agricultural Experiment Station in Geneva, New York and continued through 2016, with 4 apple cultivars ('Empire', 'Fuji', 'Gala', and 'McIntosh'), where we compared 8 tree planting densities (598, 840, 1026, 1283, 1655, 2243, 3262, and 5382 trees/ha), and two tree shapes (conic and V). At the lowest 2 densities, trees were planted on M.7 rootstock (598 trees/ha) and M.26 rootstock (840 trees/ha). At all of the higher tree densities, trees were planted on M.9. After 20 years, there was a strong negative correlation of tree planting density and trunk cross sectional area for all the cultivars and training systems, with the exception of 'McIntosh' in a V tree shape where no clear differences were observed. A different pattern for each cultivar was observed with respect to yield and planting density. High-density plantings were more appropriate for 'Fuji' and 'Gala', where conic tree shapes were better than V shapes. On the other hand, with 'Empire' and 'McIntosh' high planting density was not as beneficial. The highest yields from 'McIntosh' were realized at less than 3000 trees/ha with V tree shapes, or ∼3500 trees/ha with conic tree shapes. Planting density significantly affected firmness, soluble solids, fruit color, and fruit size. Light interception for each density and shape was measured only with 'Empire'. Planting density had a strong positive effect on light interception. There were no significant differences in interception between tree shapes through the 4th leaf, however, after that more light was intercepted by the V shaped trees. Cumulative yield was a linear function of light energy intercepted by the canopy. While V tree shapes had more light interception, conic shapes seemed to have a better efficiency converting intercepted energy into yield. Planting density improved light interception, but decreased tree partitioning because of the need for more pruning leading to unbalanced trees. Tall Spindle at high planting density seemed to be the best option for cultivars with similar bearing habits such as 'Fuji' and 'Gala'.