EXTRACTING BIOCHEMICAL INFORMATION FROM VISIBLE AND NEAR-INFRARED REFLECTANCE SPECTROSCOPY OF FRESH AND DRIED LEAVES

Visible and near-infrared reflectance data were used to estimate nitrogen and fiber fraction concentrations in dried and fresh foliage samples from 4 Mediterranean species. Reflectance was transformed into absorbance spectra and 2 pre-processing treatments (standard normal transformation and de-trending) were applied to raw spectra and their first and second derivatives. Correlograms between nitrogen or fiber concentrations and absorbance were obtained; then calibration equations using a maximum of 3 wavelengths were established from stepwise regression. Results indicate that, using pre-processing treatments, determination coefficients were very high for dried and ground samples (0.87 to 0.99), and that they remain rather high for fresh samples (0.81 to 0.93), although using different sets of wavelengths. This suggests that nitrogen and fiber concentrations in leaves may be measured through in vivo reflectance spectroscopy.