Ceptometer Deployment Method Affects Measurement of Fraction of Intercepted Photosynthetically Active Radiation

The fraction of photosynthetically active radiation a canopy intercepts (fiPAR) drives canopy level photosynthesis. There is currently no universal, repeatable fiPAR sensor deployment method. We show variability of fiPAR measurements by three sensor deployment methods, including two 1 by 1 m and one 3 by 1 m method. The deployment method biased measurements (P = 0.005) under buffelgrass (Pennisetum ciliare L) canopies. These effects were less evident in 'Alamo' switchgrass (Panicum virgatum L) and miscanthus (Miscanthus x giganteus). Canopies of these two species showed deployment method x nutrient addition interaction effects (P = 0.02), apparently driven by nutrient effects on leaf area index (LAI). We highlight potential implications of using the different deployment methods via an exercise in the application of Beer's law. As actual LAI increased, effect of deployment method on fiPAR measurements tended to diminish, suggesting in high LAI systems a universal deployment method is not as critical as it is in low LAI systems.