Vis-NIR-spectroscopy- and loss-on-ignition-based functions to estimate organic matter content of calcareous soils

ABSTRACT

The study was carried out to derive pedotransfer (PTFs) and spectrotransfer (STF) functions to estimate soil organic matter (SOM) content measured by time-consuming and expensive Walkley–Black wet combustion (W-B), using SOM content obtained from loss on ignition (LOI) and spectra reflectance bands at visible (Vis) and near infrared (NIR) regions. In total, 171 soil samples were collected from calcareous soils of southern Iran. The SOM content of the samples was determined using W–B wet combustion (SOM_W-B) and LOI at temperatures of 360 °C during 2 h (LOI_360-2); 550 °C during 3 h (LOI_550-3); and 375°C during 16 h (LOI_375-16). For the spectroscopy method, partial least squares regression (Spect_PLSR) and forward stepwise multiple linear regression (Spect_SMLR) approaches were used for function development. The LOI_360-2 procedure with R²_val of 0.9 for the validation dataset provided the best match with SOM_W-B content. Furthermore, the Spect_SMLR provided a STF using spectral reflectance bands at 495, 730, 970, 1906, 2262 and 2342 nm which predicted SOM_W-B with R²_val of 0.87. Results indicated both the Spect_SMLR and LOI_360-2, as easy and inexpensive approaches, could be recommended to accurately assess SOM content of calcareous soils.

KEYWORDS:

• Partial least squares regression
• pedotransfer function
• spectral reflectance bands
• spectrotransfer functions
• stepwise multiple linear regression

Disclosure statement

No potential conflict of interest was reported by the author(s).

Additional information

Funding

This work was supported by the Shiraz University [96GRC1M148056].