When light interception exceeds 70 per cent, flower bud formation and the production of high quality fruit may be reduced. This is because a high proportion of the tree canopy is shaded.
Light interception and shade (cont from last issue)
In these trees production is reduced in the shaded zones and yield per hectare is therefore not correlated with percentage light interception.
Research in the UK, USA and NZ clearly show that reduced sunlight can have serious effects on yield, fruit maturity and external and internal qualities of fruit.
Apart from inferior flower bud formation, insufficient light exposure may lead to a reduction in fruit size and skin colour, and to lower contents of soluble solids (sugar) and starch content in the fruit, whereas firmness and total acidity may be increased.
Shade affects leaf activity resulting in a decrease in leaf photosynthesis. Shade also has a bad effect on leaf structure, leaf thickness and leaf mass per unit area.(shade 8).
As the effects of shade on fruit and leaf characteristics are so clear, you do not need sophisticated light measuring equipment to determine whether the canopy has too much internal shading. The fruit quality and leaf characteristics in different areas of the tree’s canopy give a clear indication.
Consequently, good orchard management aims at a high level of light interception coupled with a minimum of within-tree shading.
Through a careful assessment of the tree’s growth patterns and an understanding of its responses to certain pruning methods, too much shading can be avoided, or brought under control. Once under control, yield, size, colour and quality of fruit will be maximised.
Shade and mineral nutrition
Sunlight within the canopy controls distribution of mineral elements and carbohydrates.
Well-exposed portions of the tree will have leaves with high levels of leaf nitrogen, while shaded portions have lower levels.
(cont next issue)
See this article in Tree Fruit February 2022
