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Diurnal light interception and a computer model of light interception by hedgerow apple orchards.
There was a marked diurnal variation of light interception by hedgerow orchards on sunny days in June and July. This variation was considerably reduced later in the season, with a lower solar track and an increase in the proportion of diffuse light. A computer model was constructed assuming that the hedgerows were triangular in cross-section, that the shading structures were distributed uniformly throughout the hedgerow volume, that light attenuation was a logarithmic function of shading structure, and that the various shading structures (leaves, fruits and branches) did not interact with each other. The computer model, based on data from 3 hedgerow spacings, agreed closely with observed direct and diffuse light interception from May to December. The model was used to examine the effects of row orientation on light interception and of the reduction in light interception incurred by growing the trees as hedgerows rather than as a continuous canopy. This reduction depended upon spacing and leaf area but, at conventional hedgerow spacings, could be as high as 1/5 in mid-July.