Direct Comparison between Visible Near- and Mid-Infrared Spectroscopy for Describing Diuron Sorption in Soils

摘要

Both visible near-infrared (VNIR) and mid-infrared (MIR) spectroscopy have been claimed to better predict pesticide sorption in soils than other methods. We compared the performances of VNIR and MIR spectroscopy for predicting both organic carbon content (f_(oc)) and the sorption affinity (K_d) of diuron in 112 surface soils from South Australia. Separate calibration models were developed between VNIR and MIR spectra, and f_(oc) and K_d using partial least-squares (PLS) regression. MIR clearly outperformed VNIR for predictions of both f_(oc) and K_d in soils. Correlation (R~2) and accuracy (RPD) indices were 0.4 and 1.3 for the VNIR-PLS model versus 0.8 and 2.3 for the MIR-PLS model, respectively, for K_d prediction. PLS loadings for sorption prediction were compared in terms of the soil information they contained. While VNIR loading did not include any direct spectral information regarding soil minerals, MIR loading included peaks associated with sand, clays, and carbonates. Perhaps by better predicting f_(oc) and integrating the effects of OC as well as minerals, the MIR-PLS model provided a better prediction for diuron K_d values in our calibration set.