Prediction of loblolly pine wood properties using transmittance near-infrared spectroscopy

Near-infrared (NIR) spectroscopy is a rapid nondestructive technique that has been used to characterize chemical and physical properties of a wide range of materials. In this study, transmittance NIR spectra from thin wood wafers cut from increment cores were used to develop calibration models for the estimation of alpha-cellulose content, average fiber length, fiber coarseness, and lignin content in the laboratory. Eleven-year-old trees from two sites were sampled using 12-mm increment cores. Earlywood and latewood of ring 3 and ring 8 from these samples were analyzed in the laboratory using microanalytical methods for alpha-cellulose content, average fiber length, fiber coarseness, and lignin content. NIR calibrations and laboratory measurements based on one site were generally reliable, with coefficients of determination (R-2) ranging from 0.54 to 0.88 for average fiber length and alpha-cellulose content, respectively. Predicting ring 8 properties using ring 3 calibration equations showed potential for predicting alpha-cellulose content and fiber coarseness, with R-2 values of approximately 0.60, indicating the potential for early selection. Predicting the wood properties using the calibration equations from one site to predict another showed moderate success for alpha-cellulose content (R-2 = 0.64) and fiber coarseness (R-2 = 0.63), but predictions for fiber length were relatively poor (R-2 = 0.43). Prediction of lignin content using transmittance NIR spectroscopy was not as reliable in this study, partially because of low variation in lignin content in these wood samples and large errors in measuring lignin content in the laboratory.