Determination of organic matter in soils by FTIR/diffuse reflectance and multivariate calibration

A non-destructive method avoiding the utilization of toxic and corrosive re agents is presented as an alternative for the determination of organic matt er (OM) in soils. This method is based on a multivariate calibration proced ure using partial least squares (PLS) regression to establish the relations hip between the organic matter content in soils determined by conventional chemical measurements and by diffuse reflectance spectra in the mid-infrare d region. The spectra are presented as reflectance (R) or log(1/R) and in K ubelka-Munk (K/S) units. Several data pretreatments such as multiplicative scatter correction (MSC), smoothing, derivation and normalization of the sp ectral data were employed to improve the performance of the method. The PLS analysis on the data expressed as R and log(1/R) after smoothing, differen tiation and normalization showed better results, with RMSEPs equal to 0.63% (for R) and 0.69% (for log(1/R)) and linear correlation coefficients betwe en reference and predicted OM values equal to 0.981 (for R) and 0.972 (for log(1/R)). Copyright (C) 1999 John Wiley & Sons, Ltd.