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Cohen, S., Department of Agricultural Meteorology, ARO, The Volcani Centre, Bet Dagan 50-250, Israel
Fuchs, M., Department of Agricultural Meteorology, ARO, The Volcani Centre, Bet Dagan 50-250, Israel
A model is developed of the penetration, absorption and transmission of direct and diffuse solar radiation and that scattered by the foliage in an irregularly shaped hedgerow canopy. Its main input is a discrete two-dimensional distribution of the leaf area across a row. Parameters of the model were determined experimentally in a 22-year old Shamouti orange orchard. The leaf area and angle distributions in row cross-sections were measured six times over a span of 3 years. The leaf area index (LAI) varied from 6.1 to 8.6 from the edge to the center of the row. Row cross-sections taken through the center of the tree had the same leaf area distribution as those at mid-distance between trees. The average leaf area remained stable during the 3 years. Leaf inclination distribution was not significantly different from spherical. Leaves displayed a small, but significant azimuthal preference for the south-east. However, shape factors computed from the measured angular distributions of leaf area were close to 0.5 for direct radiation throughout the day. Leaf area distribution according to direct irradiance exposure was computed on the basis of the measured leaf angles. Leaf area in each irradiance class was within 10% of that obtained for random leaf angles. Fisheye photographs, and measurements of canopy transmission of photosynthetic radiation showed that the gap frequency followed the negative binomial distribution with an independent leaf layer thickness of 1.0. Reflectance measurements of photosynthetic and total short-wave radiation were within 1 and 4%, respectively, of the computed values. Daily courses of measured transmittance of photosynthetic radiation at five different positions showed good agreement with the model's predictions. Computations and measurements of daily canopy transmittance differed by <2%. © 1987.
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The distribution of leaf area, radiation, photosynthesis and transpiration in a Shamouti orange hedgerow orchard. Part I. Leaf area and radiation
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Cohen, S., Department of Agricultural Meteorology, ARO, The Volcani Centre, Bet Dagan 50-250, Israel
Fuchs, M., Department of Agricultural Meteorology, ARO, The Volcani Centre, Bet Dagan 50-250, Israel
The distribution of leaf area, radiation, photosynthesis and transpiration in a Shamouti orange hedgerow orchard. Part I. Leaf area and radiation
A model is developed of the penetration, absorption and transmission of direct and diffuse solar radiation and that scattered by the foliage in an irregularly shaped hedgerow canopy. Its main input is a discrete two-dimensional distribution of the leaf area across a row. Parameters of the model were determined experimentally in a 22-year old Shamouti orange orchard. The leaf area and angle distributions in row cross-sections were measured six times over a span of 3 years. The leaf area index (LAI) varied from 6.1 to 8.6 from the edge to the center of the row. Row cross-sections taken through the center of the tree had the same leaf area distribution as those at mid-distance between trees. The average leaf area remained stable during the 3 years. Leaf inclination distribution was not significantly different from spherical. Leaves displayed a small, but significant azimuthal preference for the south-east. However, shape factors computed from the measured angular distributions of leaf area were close to 0.5 for direct radiation throughout the day. Leaf area distribution according to direct irradiance exposure was computed on the basis of the measured leaf angles. Leaf area in each irradiance class was within 10% of that obtained for random leaf angles. Fisheye photographs, and measurements of canopy transmission of photosynthetic radiation showed that the gap frequency followed the negative binomial distribution with an independent leaf layer thickness of 1.0. Reflectance measurements of photosynthetic and total short-wave radiation were within 1 and 4%, respectively, of the computed values. Daily courses of measured transmittance of photosynthetic radiation at five different positions showed good agreement with the model's predictions. Computations and measurements of daily canopy transmittance differed by <2%. © 1987.
Scientific Publication
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