Effects of planting density on productive structure and light environment in 'Starking Delicious' apple trees grafted on M.26 dwarfing rootstock

Abstract

The effects of planting density on productive structure and light environment were studied in 11-year-old 'Starking Delicious' apple trees (Malus domestica Borkh.) grafted on M.26 dwarfing rootstock and trained to a central leader. 1. Low density plantings from 453 to 623 trees·ha-1 became a collection of cone-shaped trees. The trees became columnar as planting density increased. Closely spaced trees grew together, losing their individual tree identity. 2. Productive structure in the 623 trees·ha-1 plot was conifer type; it shifted to a broad leaf type with increased density of planting. 3. Fruit and leaves had similar vertical distribution. Fruit production was highest in the 623 trees·ha-1 plot, indicating that productive structure of coniferous trees has high productive potential. 4. The relationship between fruit production (Yd) and fruit production per unit leaf area (Yd/F) is represented by the Eq. (1), Yd = 1.348 + 3.109 (Yd/F), indicating that the high fruit productivity in productive structure of coniferous trees depends on high fruit production per unit leaf area. 5. The coefficient of light extinction (K) decreased with increased density of planting; that is, the fruit production decreased as K value decreased. 6. The relationship between fruit production (Yd) and light interception (LI) is approximated by the Eq. (2), Yd = -150.42 + 4.175 (LI) - 0.0273 (LI)2, provided that 69.9% ≤ LI ≥ 92.2%. The optimum light interception (LIopt) which maximizes fruit production is 76.5%. 7. The planting density and the LAI at the LIopt agreed with the optimum planting density and the optimum LAI reported previously (Kuroda and Chiba, 1999), respectively. 8. The characteristics of planting with an LIopt were unevenness of crown surface, space among canopies, and productive structure of coniferous trees. 9. From the Eqs. (1) and (2), the relationship between fruit production per unit leaf area (Yd/F) and light interception (LI) can be expressed as the Eq. (7), Yd/F = 48.816 + 1.343 (LI) - 0.009 (LI)2, where 69.9% ≤ LI ≥ 92.2%. The theoretical curve fits with the experimental data, indicating that fruit production per unit leaf area depends on light interception. These results indicate that high-density planting systems of apple trees with high fruit productions should be designed on the basis of LAI with optimum light interception. The efficiency for sunlight utilization rises because such orchard is a productive structure of coniferous trees resulting in an increase of fruit production per unit leaf then high fruit production is attained.