04232naa a2200265 a 450000100080000000500110000800800410001902200140006002400350007410000170010924501270012626000090025350008890026252025030115165300310365465300260368565300150371165300210372665300190374770000140376670000180378070000150379870000170381377301360383010621352021-06-15       2021    bl uuuu     u00u1 u    #d  a0034-42577 a10.1016/j.rse.2021.1125252DOI1 aROMERO, J.M.  aCanopy active fluorescence spectrum tracks ANPP changes upon irrigation treatments in soybean crop.h[electronic resource]  c2021  aArticle history: Received 7 October 2020; Received in revised form 4 April 2021; Accepted 22 May 2021; Available online 1 June 2021. Corresponding author: Universidad de Buenos Aires, Facultad de Agronomía, Área de Educación Agropecuaria, Buenos Aires, Argentina. E-mail addresses: aberger@inia.org.uy (A.G. Berger), gcordon@agro.uba.ar (G.B. Cordon). This work was supported by Universidad de Buenos Aires (UBACyT 2018?2020, 20020170100037BA , UBACyT20020170200118BA ). INIA La Estanzuela and INIA Salto Grande provided research facilities and economic support (INIA project CS_48_0_00 and CS_42_0_00 ). The authors also thank Damian Janavel and Leonardo Silva for field assistance. M.G.L. and G.B.C. are researcher scientists of CONICET. J.M.R. developed this work with a fellowship from CONICET (Argentina). Andres Berger also receives support from SNI_2019_1_1009653 (Uruguay).  aABSTRACT. Accurate estimation of aerial net primary production (ANPP) using remotely acquired data is one of the main challenges in both environmental monitoring and precision agriculture. Reflectance-based techniques have been widely used for decades, but detection of fluorescence emission by chlorophyll has emerged as a promising alternative in recent years. Although passive sun-induced fluorescence (SIF) monitoring has shown interesting results, the information it provides is limited to few wavelengths (Fraunhofer and telluric lines). On the other hand, active measurements of steady-state fluorescence and its spectral distribution cover the full-emission spectrum but have not been fully explored due to obvious experimental limitations. In this work we develop a novel active fluorescence measurement procedure, based on lamps and sensors mounted on a field tractor. This technique allowed the detection of the full spectrum of fluorescence emission of a plant crop for the first time in the literature. The main objective of this work was to analyze how the information based on reflectance and fluorescence, recorded by the new proposed methodology, tracks the differences caused by different irrigation treatments in the ANPP of three soybean varieties. We observed that reflectance-based vegetation indices showed limited sensitivity to these cumulative differences, as only EVI2, NDWI and SRWI were able to distinguish between rainfed and irrigation treatments in some few cases. Passive, irradiance-normalised SIF showed this same trend, but active fluorescence peak ratio (FRed/FFar-red) revealed statistically significant differences for the three cultivars studied. In addition, the latter showed a significant correlation with ANPP for two soybean varieties after correction for light re-absorption and scattering (p < 0.05, R2 > 0.5), which was observed for only EVI and foliar water status VIs among passive indicators. Active fluorescence measurements at leaf level by PAM fluorometry did not show differences between treatments in the upper part of the canopy but revealed a biomass-dependent decrease in PSII yield along the vertical axis. Our study demonstrated that fluorescence emission spectrum holds highly valuable information that might allow monitoring ANPP changes upon irrigation from remote sensing applications, and therefore should be carefully studied. Lastly, it highlights the potential of SIF retrieval at both O2-A and O2-B lines.  © 2021 Elsevier Inc.  aCanopy active fluorescence  aFluorescence modeling  aIrrigation  aPlant monitoring  aRemote sensing1 aOTERO, A.1 aLAGORIO, M.G.1 aBERGER, A.1 aCORDON, G.B.  tRemote Sensing of Environment, 15 September 2021, Volume 263, Article number 112525. Doi: https://doi.org/10.1016/j.rse.2021.112525