LIGHT DISTRIBUTION AND FRUIT QUALITY THROUGH MULTI-LAYERED TRELLIS APPLE CANOPIES

Photosynthetic photon flux (PPF) profiles were determined for mid-canopy positions on each side of the four layers of a 7-year-old Granny Smith apple trellis row, orientated 30° east of north-south. Instantaneous measurements were made every hour from 8.00 am until 6.00 pm in mid-January when the canopy had full leaf development. PPF was typically 50 μmoles m^-2 s^-1 and rarely exceeded 400 μmoles m^-2 s^-1 for the three lowest trellis layers throughout the day. Open-sky levels, for the same duration ranged between 500 and 2200 μmoles m^-2 s^-1. PPF transmission to the uppermost (4th) layer followed the open-sky pattern although modified by within-canopy location, so that the peak PPF values never exceeded 1200 μmoles m^-2 s^-1. Hourly integrals of PPF were measured for the mid-canopy position of the second lowest layer of the trellis, over 4 consecutive days in mid-January. Integrated PPF transmission confirmed the patterns of low light penetration to the lower trellis layers observed from instantaneously measured PPF.

Mean fruit fresh weight, the proportion of the total crop, and shoot specific leaf weight decreased successively down the layers of the trellis. Fruit soluble solids concentration was substantially higher in fruit from the uppermost layer. The green background colour was darker on fruit produced in the lower trellis layers.

Although the Ebro trellis conforms to HDP principles of small individual tree canopy size and a high density of trees per hectare, this study suggests that the canopy shape and row spacing result in intense shading of much of the fruit-bearing structure of the tree.

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