

Author:  J.E. Jackson 
DOI:  10.17660/ActaHortic.1981.114.4 
Abstract:
Light interception and the volume of wellilluminated 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 
= F_{max}  F_{max}e^{KL´}

L_{I} 
= F_{max} ((ln I)/(K)) or LAI if this is less

where:
 F is the fraction of available light which is intercepted, F_{max} is the fraction of available light which would be intercepted by nontransmitting 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)/(F_{max}).
 I is the level of irradiance which is taken as the lower limit for wellilluminated canopy and L_{I} 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 F_{max} for those cases where published data is not available are described.

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