Ceptometer deployment method affects measurement of fraction of intercepted photosynthetically active radiation

Abstract

The fraction of photosynthetically active radiation a canopy intercepts (fi PAR) drives canopy level photosynthesis. There is currently no universal, repeatable fi PAR sensor deployment method. We show variability of fi PAR 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 buff elgrass (Pennisetum ciliare L) canopies. These eff ects 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 eff ects (P = 0.02), apparently driven by nutrient eff ects on leaf area index (LAI). We highlight potential implications of using the diff erent deployment methods via an exercise in the application of Beer's law. As actual LAI increased, eff ect of deployment method on fi PAR measurements tended to diminish, suggesting in high LAI systems a universal deployment method is not as critical as it is in low LAI systems. © 2010 by the American Society of Agronomy.