Relationship of 2 100–2 300 nm Spectral Characteristics of Wheat Canopy to Leaf Area Index and Leaf N as Affected by Leaf Water Content1

ABSTRACTThe effects of leaf water status in a wheat canopy on the accuracy of estimating leaf area index (LAI) and N were determined in this study using extracted spectral characteristics in the 2 000–2 300 nm region of the short wave infrared (SWI) band. A newly defined spectral index, relative adsorptive index in the 2000–2300 nm region (RAI2000–2300), which can be calculated by RAI2000–2300 = (R2224–R2054) (R2224 + R2054)−1 with R being the reflectance at 2224 or 2054 nm, was utilized. This spectral index, RAI2000–2300, was significantly correlated (P < 0.01) with green LAI and leaf N concentration and proved to be potentially valuable for monitoring plant green LAI and leaf N at the field canopy scale. Moreover, plant LAI could be monitored more easily and more successfully than plant leaf N. The study also showed that leaf water had a strong masking effect on the 2 000–2 300 nm spectral characteristics and both the coefficient between RAI2000–2300 and green LAI and that between RAI2000–2300 and leaf N content decreased as leaf water content increased.