The Planar Cordon - new planting systems concepts to improve light utilisation and physiological function to increase apple orchard yield potential

D.S. Tustin, B.M. van Hooijdonk, K.C. Breen
Contemporary high density apple orchards, although very productive in historical terms, are yield-limited at 100-120 t ha-1 because their maximum fractional utilisation of sunlight is only circa 60% of total seasonally-available radiation. Previous research in New Zealand proposed a theoretical potential productivity of 169 t ha-1 for late-season cultivars if orchard light interception of 90% could be achieved. A major constraint to improving light interception by planting systems is the allocation of space between rows. Any increase in light utilisation will require closer rows and/or inclined canopies. New planting systems to increase light interception by reducing inter-row distances, whilst achieving adequate within-canopy irradiance for high quality fruit, are being studied in New Zealand. Rows spaced at 1.5 to 2 m apart require new tree forms with narrow planar canopies for both eco-physiological and practical reasons. Tree architecture comprises two opposing, not-quite horizontal cordon leaders along the row, each subtending five vertical non-branched fruiting stems, 30 cm apart, to create narrow planar trees, 3 m long, less than 0.5 m wide, and with an anticipated height of 3-3.5 m. Four cultivars in a first prototype, planted at 1667 (2 m inter-row) and 2222 (1.5 m inter-row) trees ha-1 yielded from 9 to 29 t ha-1 in their second year. Fractional light interception of 2- and 3-year-old plantings characterised young-tree planar cordon canopy row spacing effects, in comparison with a same-aged 1.5×3.5 m tall spindle system. Productivity traits from 3-year-old systems planted at 1.5 and 2 m row spacing and between vertical and narrow vee planar canopy variants of two-year-old planting systems indicate productivity gains over the three-dimensional tall spindle canopy configuration. In additional to light interception, these results also indicate that growth processes regulating the allocation fate of annual growth resources are important factors determining the productivity potential of apple orchards. Evidence for plasticity of resource partitioning into fruit development in response to different manipulations of tree architecture are drawn from our studies of new planar cordon systems and with conventional tall spindle planting systems.
Tustin, D.S., van Hooijdonk, B.M. and Breen, K.C. (2018). The Planar Cordon - new planting systems concepts to improve light utilisation and physiological function to increase apple orchard yield potential. Acta Hortic. 1228, 1-12
DOI: 10.17660/ActaHortic.2018.1228.1
light interception, productivity, harvest index, resource allocation

Acta Horticulturae