Evaluating the particle densities of subarctic soils using pedotransfer functions and vis–NIR spectroscopy

Abstract

The particle density (ρs) is a fundamental physical property needed for calculating the soil porosity and phase distributions. While ρs is often estimated using soil organic matter (SOM) content and particle size distribution, the specific densities of each soil component remain unclear in a subarctic agricultural setting. This study aimed to evaluate the ρs of soils from Southwest Greenland using a three-compartment model (3CM) based on the mixing ratio of SOM derived from loss-on-ignition, mineral particles <20 μm (FC), and mineral particles ≥20 μm (CC). We further evaluated the accuracy of the 3CM against pedotransfer functions (PTFs) and visible near-infrared (vis–NIR) spectroscopic models. A total of 324 soil samples from 16 Greenlandic agricultural fields were investigated, covering a wide range in SOM content (0.021–0.602 kg kg–1) and clay content (0.020–0.185 kg kg–1). Despite their high SOM content, the Greenlandic soils exhibited relatively high ρs (1.936–3.044 Mg m–3), which together with a large SOM/organic carbon ratio of 2.16 indicated a high SOM density of 1.493 Mg m–3. The 3CM fit on all soils indicated FC and CC densities of 3.047 and 2.713 Mg m–3, respectively, while a subset of soils (n = 203) from the same geological setting resulted in FC and CC densities of 2.738 and 2.731 Mg m–3. Prediction accuracy of the 3CM (RMSE = 0.067 Mg m–3) was similar to PTFs (RMSE = 0.068–0.070 Mg m–3) and better than vis–NIR spectroscopic models (RMSE = 0.091 Mg m–3).