Prediction of soil organic carbon using VIS-NIR spectroscopy: Application to Red Mediterranean soils from Croatia

Abstract

The objectives of this research were: (i) to assess the accuracy of diffuse reflectancespectroscopy (DRS) in predicting the soil organic carbon (SOC) content, and (ii)determine the importance of wavelength ranges and specific wavelengths in the SOCprediction model. The reflectance spectra of a total of 424 topsoils (0-25 cm) sampleswere measured in a laboratory using a portable Terra Spec 4 Hi-Res MineralSpectrometer with a wavelength range 350-2500 nm. Partial least squares regression(PLSR) with leave-one-out cross validation was used to develop calibration models forSOC prediction. The accuracy of the estimate determined by the coefficient ofdetermination (R2), the concordance correlation coefficient (ρc), the ratio ofperformance to deviation (RPD), the range error ratio (RER) and the root mean squareerror (RMSE) values of 0.83, 0.90, 2.22, 14.2 and 2.47 g C kg-1 respectively, indicatedgood model for SOC prediction. The near infrared (NIR) and the short-wave infrared(SWIR) spectrums were more accurate than those in the visible (VIS) and short-wavenear-infrared (SWNIR) spectral regions. The wavelengths contributing most to theprediction of SOC were at: 1925, 1915, 2170, 2315, 1875, 2260, 1910, 2380, 435, 1960,2200, 1050, 1420, 1425 and 500 nm. This study has shown that VIS-NIR reflectancespectroscopy can be used as a rapid method for determining organic carbon content inthe Red Mediterranean soils that can be sufficient for a rough screening.