Measurement and Analysis of the 3D Spatial Distribution of Photosynthetically Active Radiation in Maize Canopy

An experiment to measure the 3D PAR (Photosynthetically Active Radiation) distribution in maize canopy was designed. The following results have been achieved through 3D PAR analysis from this experiment. (1) The averaged PAR at different depths in maize canopy was decreased with the increase of accumulated LAI by exponential law. The decrease trend of PAR transmittance of maize canopy was very similar for different density at same time and weather. But the extinction coefficient varied evidently with different weather and different sunshine angle even for the same canopy. (2) There were much more flecks of sunlight in upper canopy. The PAR transmittance in the flecks was high and varied very slightly. Within the lower canopy, the averaged PAR was very low and there were very few flecks of sunlight. The maximum PAR transmittance was also very low. (3) Lower maize planting density would increase flecks of sunlight and PAR transmittance evidently in canopy bottom. (4) PPFD (Photosynthetic Photon Flux Density) and maximum PAR transmittance in maize canopy was badly decreased in cloudy days. This study might provide some references for the simulation of 3D light distribution and experiment design of 3D light measurement in crop canopy.