Limitations to Use of Infrared Spectroscopy for Rapid Determination of Carbon-Nitrogen and Wood Density for Tropical Species

Abstract

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.