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Optimization of the light regime within the fruit tree canopy

For students

3 min read

Light directly determines the canopy structure, leaf development, and photosynthetic efficiency of a fruit tree. Good illumination stimulates shoot growth, but without control, it quickly leads to overcrowding. Shaded branches inside the canopy begin to die off, causing the tree to temporarily self-thin, after which the cycle of rapid growth repeats. To break this circle, the agronomist must regulate the light regime through pruning.

  • Optimal leaf illumination — 70% of full sun
  • Threshold for normal fruiting — 30% of full sun
  • Minimum for shade leaf operation — 8–10% of full sun
  • Thickness of the productive leaf canopy — 0.8–1.5 m

The unevenness of canopy illumination is noticeable even at a young age. The southern and eastern sides of the tree are better illuminated; therefore, by the age of 10, the length of their annual growth is almost 1.5 times that of the northern and western sides. 37% of leaves and 32% of fruits are formed on the south and east, while the center of the canopy gradually falls into shade. With age, this light regime deficit progresses: in 25–30-year-old trees, the empty, non-productive zone in the center can occupy from 20–30% to 50% of the total canopy volume.

Рис. 49. Освещение округлой кроны в зависимости от размера: I – разрез по вертикали; II – разрез по горизонтали на высоте h по линии АБ.
Fig. 49. Illumination of a rounded canopy depending on size: I – vertical section; II – horizontal section at height h along line AB.
Рис. 50. Освещение глубинных участков кроны в зависимости от плотности размещения деревьев: А – при разреженном расположении; Б – при загущении в ряду.
Fig. 50. Illumination of deep canopy areas depending on tree planting density: A – with sparse spacing; B – with overcrowding in the row.
Рис. 51. Влияние формы и объема кроны на величину затененной части: 1 – пирамидальная; 2 – шаровидная; 3 – широкораскидистая; 4 – вертикально-уплощенная типа пальметты; 5 – вертикально-уплощенная в сплошной кроне ряда; 6 – осветленная с удалением части це
Fig. 51. Influence of canopy shape and volume on the size of the shaded part: 1 – pyramidal; 2 – spherical; 3 – wide-spreading; 4 – vertically flattened like a palmette; 5 – vertically flattened in a solid canopy row; 6 – opened by removing part of the central leader and canal-fan shaped; 7 – horizontally flattened.
Рис. 52. Освещение кроны в зависимости от ее возраста и структуры: А – двадцатипятилетняя (сильно загущенная); Б – пятнадцатилетняя (среднезагущенная); В – десятилетняя (хорошо сформированная). Цифры показывают освещение разных участков кроны в процентах
Fig. 52. Canopy illumination depending on its age and structure: A – twenty-five-year-old (heavily overcrowded); B – fifteen-year-old (moderately overcrowded); C – ten-year-old (well-formed). Figures show illumination of different canopy areas as a percentage of open area illumination.

Influence of planting density and row structure on the light regime

The center of the canopy becomes bare especially quickly in overcrowded orchards without regular thinning. With planting schemes of 8 × 3 m or 8 × 2 m, the branches of adjacent trees close into a solid row. The active leaf canopy then operates only on the periphery to a depth of 1.5 m. The entire inner part of the 6–7-meter row is shaded and completely excluded from fruiting.

Parameters of the non-productive zone in a solid row Size, m
Width at the base 3–4
Height from 1 to 4

Do not allow the illumination inside the canopy to drop below 30% of the full open area. In conditions of deep shading, photosynthesis is inhibited, and ripening fruits lose their cultivar qualities: they become smaller, deform, and fail to reach full color and sugar content.

Orienting rows from north to south ensures the most favorable illumination of the solid row canopy throughout the day and prevents excessive leaf overheating at noon.

Рис. 53. Направление рядов с севера на юг обеспечивает наиболее благоприятное освещение сплошной кроны ряда в течение дня и предупреждает излишний перегрев листьев в полдень.
Fig. 53. Orienting rows from north to south ensures the most favorable illumination of the solid row canopy throughout the day and prevents excessive leaf overheating at noon.
Рис. 56. Размещение листьев и плодов в кроне 10-летних деревьев яблони сорта Антоновка обыкновенная (в процентах), на южной, северной стороне и в центре кроны.
Fig. 56. Distribution of leaves and fruits in the canopy of 10-year-old Antonovka Obyknovennaya apple trees (in percent), on the south, north side, and in the center of the canopy.

Vertically flattened canopies, such as a palmette or a living fruit wall, effectively solve the problem of sunlight shortage deep in the tree. The thinner the canopy, the more evenly light is distributed between the leaves and the ripening fruits. However, it is important to maintain a balance here. Excessive narrowing of the wall increases the area of empty inter-row spaces, which reduces the overall productivity of the orchard per hectare.

A fruit wall that is too narrow leads to a loss of yield per unit area due to inefficient use of inter-row space.

Рис. 54. Для предупреждения длительного затенения соседними рядами расстояние между плодовыми стенками d должно быть в 1,5 раза больше высоты деревьев h (допустимо отношение 1:1).
Fig. 54. To prevent prolonged shading by adjacent rows, the distance between fruit walls d should be 1.5 times the tree height h (a 1:1 ratio is acceptable).

How to calculate canopy dimensions and row direction

To avoid mutual shading of rows, it is necessary to strictly control tree dimensions and the width of technological passages. The leaf canopy in any projection should not exceed critical thickness, otherwise the center of the canopy will be in constant shade. When designing a planting scheme and conducting contour pruning, it is important to be guided by the calculated parameters of the light regime.

  • Leaf canopy thickness — up to 1.5–2 m
  • Ratio of inter-row to wall height — from 1:1 to 1.5:1

The optimal solution for uniform illumination is to orient rows from north to south. With this orientation, the canopy receives sufficient sun throughout the day. At the same time, the leaves and fruits are reliably protected from overheating during the hottest noon hours.

The relief of the plot also makes adjustments to standard calculations. On southern slopes, the distance between rows can be reduced without the risk of losing light. On northern slopes, row spacing must, conversely, be increased to protect neighboring trees from deep shading.

Рис. 55. Расстояние между деревьями (рядами деревьев) на северном склоне должно быть больше, чем на южном.
Fig. 55. The distance between trees (tree rows) on a northern slope must be greater than on a southern one.

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