Critical analysis of methods to estimate the fraction of absorbed or intercepted photosynthetically active radiation from ground measurements: Application to rice crops

Continuous and accurate ground measurements of the fraction absorbed (fAPAR) or intercepted (fIPAR) photosynthetically active radiation by green canopy components is important to monitor functioning. fAPAR fIPAR are sensitive illumination conditions non-green during senescence stage. While several methods have been developed estimate in field from different including AccuPAR, LAI-2200 Digital Hemispheric Photograph Photography (DHP), differences among these still need more investigations. The principles on which they based first reviewed with due attention assumptions used approximations made. Two campaigns conducted 2012 2013 northeastern China over paddy rice fields were then compare measured using DHP LAI-2200. Results demonstrated that considering only light transmittance (fIPAR), LAI-2200, a good proxy computed AccuPAR four fluxes balance. However, when senescing, downward looking method recommended since it directly measures elements. Methods upward (DHP upward, LAI-2200) cannot distinguish between senescent vegetation Corrections independent ratio area index (GAI) plant (PAI) (GAI/PAI) be this case, while assuming elements well mixed volume. Downward appears preferred for relatively short dense canopies such as does not disturb canopy, allows simulate any conditions.