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ISHS Acta Horticulturae 114: Symposium on Research and Development on Orchard and Plantation Systems

THEORY OF LIGHT INTERCEPTION BY ORCHARDS AND A MODELLING APPROACH TO OPTIMIZING ORCHARD DESIGN

Author:   J.E. Jackson
Abstract:
Light interception and the volume of well-illuminated canopy are key factors in orchard productivity but are difficult and time consuming to measure. A modelling approach has been devised to enable rapid calculation of the potential efficiency of any kind or age of orchard in these respects. The appropriate equations are

F = Fmax - Fmaxe-KL´
LI = Fmax ((ln I)/(-K)) or LAI if this is less

where:

  1. F is the fraction of available light which is intercepted, Fmax is the fraction of available light which would be intercepted by non-transmitting trees or hedgerows of the same shape and arrangement, K is a light extinction coefficient (taken as 0.6 for apple) and L´ is (LAI)/(Fmax).
  2. I is the level of irradiance which is taken as the lower limit for well-illuminated canopy and LI is the leaf area index within this part of the canopy. The volume which is 'well illuminated' can then readily be calculated from knowledge of leaf density per unit tree volume.

The use of these equations and simple ways of determining Fmax for those cases where published data is not available are described.

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