DEVELOPMENT AND APPLICATION OF A NOVEL SYSTEM FOR MEASURING CANOPY LIGHT INTERCEPTION IN PLANAR ORCHARDS
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Interception of photosynthetically active radiation (PAR) is fundamental to tree fruit canopy growth, fruit yield, and quality. Many studies have investigated PAR in traditional hedgerow orchard orchards but there are few reports from modern planar canopy architectures. This research aimed to develop a system capable of large-scale measurement of PAR interception and evaluate light relations in modern planar orchard systems. A mobile measurement system capable of continuously collecting high-density PAR data was developed. This system could maintain a constant spatial resolution 0.01 × 0.10 m/sample (traveling direction × perpendicular to traveling direction) between 0-3.8 km/h. A graphic data acquisition interface was created for real-time monitoring data acquisition process. The mobile measurement system was utilized to develop a canopy mapping method and a light interception conversion method for obtaining the same measure basis. The canopy mapping method was designed to visualize the canopy shadow as though the sun were directly overhead (i.e., correcting distortion caused by the azimuth and zenith angles). This method was validated in a Y-trellis sweet cherry orchard at dormant and full canopy stages with average relative error of 3.4%±3.1% and 4.8%±2.6% respectively. An additional study determined the best time to take single measurement representative of daily canopy PAR interception based on diurnal and seasonal data. The optimum measurement time to represent diurnal PAR interception in a vertical fruiting wall architecture of sweet cherry was from 09:30 h to 10:30 h (daylight saving time) with ±10% tolerance interval of daily light interception. Canopy light interception varies according to measurement time and/or location, resulting different measure basis. Therefore, a light interception conversion method was developed to obtain light interception on the same measure basis. The conversion method was validated in a vertical planar orchard with overall root mean square error of 0.03 and mean absolute percentage error of 5.32%. This research has generated a tool and guidelines for its use in obtaining accurate canopy light interception in modern planar orchard systems. Outcomes of this research can be used to extract individual canopy light interception and its dynamics within/between canopies regardless of orchard location or measurement time.