Assessment of F(v)/F(m) 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 the F(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.