Limitations to use of infrared spectroscopy for rapid determination of Carbon-Nitrogen and wood density for tropical species

Infrared (IR) spectroscopy was used as a rapid and non-destructive method to determine carbon (C) nitrogen (N) and tree wood density.A total of 82 sample cores were scanned in the reflectance mode from 4000 to 400 cm-1 for mid-infrared (MIR) spectra and from 8000 to 4000cm-1 and 11000-4000cm-1 for near infrared (NIR) spectra. The reference values for C and N were measured using combustion method while wood density was calculated using auger method. Calibration equations were developed using partial least-squares and first derivative spectra. Root mean square error (RMSEP) was used to calculate prediction error. Prediction of Cusing MIR spectra gave R2 = 0.59 RMSEP = 0.02; NIR spectra R2 = 0.50 RMSEP = 0.02 whileN prediction usingMIR spectra had R2 = 0.54 RMSEP = 0.22; NIR spectra R2 = 0.48 RMSEP =0.24. Wood density prediction was fair for MIR (R2= 0.79 RMSEP = 0.14); NIR (R2= 0.69 RMSEP = 0.17).Improved predictions using NIR were for extendedspectral range;though accuracies were inferior to MIR. Both MIR and NIR models showed good potentials to be used as rapid and cost effective method of predicting C-N and wood density

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