Determining leaf nitrogen concentration of broadleaf tree seedlings by reflectance measurements
1991
St-Jacques, C. | Bellefleur, P.
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 mn. 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.
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