Macadamia planting density has a strong effect on orchard productivity in a decade-long trial

Australian macadamia (Macadamia integrifolia x M. tetraphylla) orchards are generally planted at low densities, taking ten years or more to reach maximum yield. Increasing planting density provided a substantial leap in the orchard productivity of temperate tree crops. Inspired by this transformation, the impact of planting density was evaluated in an experimental macadamia orchard, established in Central Queensland, Australia. Over ten years, three planting densities from high (5 x 2 m; 1,000 trees ha-1) to medium (6 x 3 m; 556 trees ha-1) and conventional low density (8 x 4 m; 313 trees/ha) were compared across two scion cultivars (‘HAES 741’, ‘HV A203’). High planting density increased early orchard productivity as expected, and ten years from planting, its cumulative yield per hectare was around 43% higher than that of the low planting density in both cultivars. This increase in early productivity is likely due to the greater canopy volume and light interception in the early life of the high-density system. However, the pruning requirements in the high-density system were relatively higher and had an adverse e ect on yield in this system. Thus, we foresee that maintaining high production beyond ten years will in part depend on appropriate canopy management. Concerns about an e ect of high planting density on nut quality are not justified, as our data shows no di erences between densities in regard to various nut quality parameters. Overall, increasing the planting density may be a valuable tool for improving macadamia orchard profitability. It will, however, require the development of a sustainable canopy management strategy to suit this intensified system.