Assessment of Fv/Fm absorbed by wheat canopies employing in-situ hyperspectral vegetation indexes

Chlorophyll fluorescence parameter of F-v/F-m, as an important index for evaluating crop yields and biomass, is key to guide crop management. However, the shortage of good hyperspectral data can hinder the accurate assessment of wheat F-v/F-m. In this research, the relationships between wheat canopy F-v/F-m and in-situ hyperspectral vegetation indexes were explored to develop a strategy for accurate F-v/F-m assessment. F-v/F-m had the highest coefficients with normalized pigments chlorophyll ratio index (NPCI) and the medium terrestrial chlorophyll index (MTCI). Both NPCI and MTCI were increased with the increase in F-v/F-m. However, NPCI value ceased to increase as F-v/F-m reached 0.61. MTCI had a descending trend when F-v/F-m value was higher than 0.61. A piecewise F-v/F-m assessment model with NPCI and MTCI regression variables was established when F-v/F-m value was <= 0.61 and >0.61, respectively. The model increased the accuracy of assessment by up to 16% as compared with theF(v)/F-m assessment model based on a single vegetation index. Our study indicated that it was feasible to apply NPCI and MTCI to assess wheat F-v/F-m and to establish a piecewise F-v/F-m assessment model that can overcome the limitations from vegetation index saturation under high F-v/F-m value.