© 1991 Heron Publishing—Victoria, Canada
Determining leaf nitrogen concentration of broadleaf tree seedlings by reflectance measurements
Claude St-Jacques and Pierre Bellefleur
Centre de recherche en biologie forestière, Département des sciences forestières, Faculté de foresterie
et de géomatique, Université Laval, Ste-Foy, Québec, Canada G1K 7P4 / Received February 21, 1990
Summary
The accuracy of estimating leaf nitrogen concentration by leaf reflectance measurements was investigated with 3- or 4-year-old
field-grown seedlings of white ash (Fraxinus americana L.), red oak (Quercus rubra L.), bur oak (Quercus macrocarpa Michx.), and American basswood (Tilia americana L.). The highest absolute correlations (> –0.8) between leaf reflectance and leaf nitrogen concentration were measured in
the red region of the spectrum at wavelengths of 600–700 nm. These results differ from those reported for herbaceous and conifer
species which show the closest correlation in the green region of the spectrum at wavelengths around 540 nm. Linear regression
analysis demonstrated significant correlations (P = 0.0001) between leaf nitrogen concentration, which varied over an approximately twofold range, and reflectance at the wavelength
of maximum correlation for sets of 40 leaves of each species. The coefficients of determination (r2) for red oak, American basswood, white ash and bur oak were 0.32, 0.53, 0.69 and 0.70, respectively. The regression equations
were used to estimate leaf nitrogen concentration from reflectance in sets of 30 leaves of each species, which were collected
in the season following the calibration measurements. Percent leaf nitrogen concentration estimated by reflectance differed
from Kjeldahl-determined values by from 0.04% in white ash to 0.33% in basswood. Greater accuracy in estimating leaf nitrogen
concentration from reflectance was achieved with a prediction equation based on calibration data for all species combined.
