ISHS Acta Horticulturae 276: II International Symposium on Computer Modelling in Fruit Research and Orchard Management
EFFECTS OF ORCHARD GEOMETRY ON LIGHT DISTRIBUTION |
| Author: | P. S. Wagenmakers |
| Abstract:
A three-dimensional model has been developed to simulate light distribution in various orchard systems. The model is based on Van Kraalingen (1989) but adapted for tree shape and foliage distribution. Trees may be conical, cylindrical, parabolical or of intermediate shape. Diameter and height of the tree crowns may vary and leaves, branches and fruit are assumed to be uniformly distributed throughout a crown. Any number of equally shaped trees may be located in any arrangement desired. The model calculates numerically light transmission through crowns at a given position, separating direct light from diffuse radiation. The model mimics quite well observed light measurements in various orchard systems and it might therefore replace some field observations in the future. However, occasionally the model tends to overestimate light transmission. Errors might be caused by the incorrect assumption of a given leaf area for all trees, for it can vary highly between trees in a given system. The model outcomes depend also on tree shape, which was actually more variable than assumed. The effect of windbreaks on light interception was omitted by the model, but has had an effect on part of the observed plots. Furthermore, the light observations were done under overcast radiation, yet probably not as uniform as assumed in the model. Even under cloudy conditions, most radiation comes directly from the sun. So, time of the day might have influenced the light readings. Model calculations showed the effect of tree spacing on light transmittance under a given tree. Tree density, shape and leaf area per tree were kept similar for the given spacings. Transmission of diffuse light was much lower under the central tree in a staggered three-row bed than under a similar tree located in a single row. A tree at the periphery of the staggered three-row bed transmitted as much light as a single-row tree. Trees in the centre of a five-row bed with an oblique walking path were better illuminated than in a staggered three-row bed, but less than in a single row. The tree at the periphery of the five row received even more light than a similar tree in a single row. This is probably due to sidewards illumination from both the alley way and the walking paths. The effect of tree height on canopy light transmission interacted with leaf area density per tree. When trees varied in height between 1.5 m and 2.5 m, light transmission increased 15 % when leaf density remained constant. Under these constraints, leaf area index increased from 2.2 to 3.8. On the other hand, at a similar leaf area per tree, the largest trees intercepted only 7 % more light. Thus, leaf density must be taken into account when calculating the optimal tree height. | |
Download Adobe Acrobat Reader (free software to read PDF files) | |
