Gas diffusion characteristics of agricultural soils from South Greenland

The Arctic is warming at twice the global average, which may impact agricultural production in Greenland. Therefore knowledge of the functional properties of Greenlandic soil resources is necessary. The relative soil gas diffusivity [the soil gas diffusion coefficient (D_p)–free-air diffusion coefficient (D_o) ratio] is the chief parameter controlling gas transport in soils. Predictions of D_p/D_o are needed to estimate root zone aeration and terrestrial greenhouse gas fluxes. We used existing models to analyze the D_p/D_o of soils from Greenlandic fields and a pore connectivity index (C_ip) to infer their degree of structural development and identify the main parameters controlling D_p/D_o. In total, 201 × 3 intact 100-cm³ soil samples were sampled across six fields with clay and organic C contents of 0.016 to 0.089 and 0.016 to 0.105 kg kg⁻¹, respectively. The D_p/D_o was measured with the one-chamber nonsteady-state method at soil water potentials between –10 and –1,000 cm H₂O. Accurate determination of total porosity (Φ) was ensured by calibrating a particle density model on 129 samples. The soils exhibited a less developed structure and highly tortuous pore networks, resulting in low D_p/D_o as a function of air-filled porosity (ε). Density-corrected models with air saturation (ε/Φ) reduced the RMSE. Furthermore, C_ip at –1,000 cm H₂O soil water potential increased linearly with dry bulk density (ρ_b), suggesting that ρ_b is a key controller of D_p/D_o, which is important for planning cultivation practices for Southern Greenlandic soils. Lastly, we found that an air saturation >35% is required for adequate soil aeration.