Deciphering the link between SIF, ANPP and RUE dynamics in perennial forage crop mixtures

• The ability of SIF to estimate ANPP and RUE was evaluated in different forage covers. • Seasonal monitoring of forage covers (alfalfa, tall fescue , mixtures plots). • Alfalfa and mixture plots showed constant RUE and SIF Yield upon APAR variations. • SIF turned out to be an interesting monitor of ANPP in alfalfa and mixture plots. • Tall fescue's RUE decreases with rising APAR, breaking SIF-ANPP link. Remote sensing estimation of aerial net primary production (ANPP) is a key challenge in precision agriculture and environmental monitoring. The Monteith model serves as the main conceptual frameworkin pastures.Sun-induced fluorescence (SIF), closely linked to photosynthesis, is a promising candidate for ANPP estimations when radiation use efficiency (RUE) undergoes physiological changes. Our aim was to analyze SIF´s ability to estimate ANPP and RUE in forage covers with different structural and physiological characteristics. Moreover, we aimed to determine the underlying mechanisms driving these correlations. We performed a proximal sensing experiment by generating differential forage covers (alfalfa, tall fescue, and mixtures), measured across different seasons. Alfalfa and mixture plots have shown fairly constant RUE and fluorescence emission efficiency (SIF Yield ) upon APAR variations. This caused SIF to be an interesting monitor of ANPP (R 2 ∼ 0.5), because of their strong link with APAR. On the other hand, tall fescue showed decreasing RUE when increasing APAR, which weakens ANPP-APAR correlation (R 2 ∼ 0.38). Also, reduced escape fraction weakens SIF-APAR correlation (R 2 ∼ 0.09). Consequently, the ANPP-SIF correlation disappears (R 2 ∼ 0.02). This is one of the first remote sensing studies analyzing the biomass available for harvest in a field managed according to forage agronomic criteria. Our findings support the use of SIF as a monitor of ANPP of forage crops when RUE and SIF Yield can be assumed to be constant upon APAR variations. Nevertheless, correlations may not be extrapolated between different crops; careful attention must be paid to RUE variations upon APAR.