Gaps in tree canopies are big money losers

Too much sunlight – and therefore potential crop – is being wasted in many orchards. One of the major reasons that mature orchard productivity is sub-optimal, is that gaps between trees in the row, and too much wasted space between rows, are reducing the total canopy surface (cropping) area per hectare that the tree density and specific orchard system is designed for.

Gaps and too much air between the trees are common problems especially with apple trees on dwarfing rootstocks that are overcropped before the trees’ canopies have filled their spaces. As well, air turbulence and tree transpiration are increased by gaps between trees.

Yield is directly linked to the amount of sunlight captured (intercepted) by the tree’s canopy. The more light the trees capture, the more crop they can carry. Sunlight that hits the orchard floor is mostly wasted. Use of reflective material on the orchard floor will help reflecting sunlight back into the lower canopy but is not economically justified if the canopies contain many gaps.

It is easy to avoid gaps and at the same time maximize canopy surface area per hectare and yield, by developing upright or V-shaped two-dimensional continuous thin hedges. If you combine this with closely planted trees that have simple tree structures, you are on a win-win pathway.

A simple tree structure is a tree that has two leaders dressed with short fruiting units – no branches, because branches make management and productivity of fruit trees difficult and costly.

The leader is the primary and permanent structure of the tree. Fruiting units, collectively called fruiting wood, are short (100-300 mm) pieces of 1-2-and 3-year-old wood with leaves and vegetative and reproductive spurs, laterals and buds. Fruiting units are continuously renewed to keep the fruiting wood young and productive.

The highest possible light interception for sustainable high yields of good quality fruit is about 70 per cent, and only achievable with continuous canopies with total surface (cropping) areas of around 11,000 square meters per hectare. This allows alleyways between rows for orchard equipment to pass through.

With continuous canopies there are no gaps and no tree individuality. Each leader is a copy of many, allowing precise crop management per unit of canopy surface area.

You may not realise what fruit production you are losing every year, because gaps in the canopy between trees and between rows is a waste of space – space that should be occupied with fruiting wood, leaves and fruit, not fresh air.

Written by Bas van den Ende, who was a researcher at the Tatura Research Institute, author, and former consultant in fruit production. Contact: advhort@bigpond.net.au

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