Soil-air phase characteristics: Response to texture, density, and land use in Greenland and Denmark.

Soil aeration is a key parameter for sustainable and productive agriculture. The intensification of agricultural activity in Greenland involves land use (LU) and LU change, affecting the soil–air phase. The combined effects of natural compaction (bulk density, ρ _b), texture (texture uniformity index; TUI), and LU on the soil–air phase of subarctic soils are not well known. This study aims to identify and compare the main drivers for air-filled porosity (ε) and soil-structure changes within and across sites in Greenland and Denmark. We analyzed comprehensive data sets of ε, relative gas diffusivity D _p/D _o), and air-permeability (k _a) measured on intact soil samples from South Greenland (pasture) and Denmark (cultivated, urban, and forest). The mechanical robustness of the air phase was evaluated by linear models of ε as a function of ρ _b (H-model). The ratio of k _a to D _p/D _o served as a soil-structure index (Ω); the latter significantly correlated to TUI. The Greenlandic pasture soils did not show signs of well-developed soil structure (low Ω-values), whereas low H-values suggested the soils were mechanically robust compared to similar-textured cultivated soils. The soil–air characteristic curve (ε vs. pF) was parameterized, and the moisture control parameter was accurately predicted by TUI and LU (R ² =.95). Overall, the ρ _b was found to control the air-phase functions within a field. However, considering changes in ε-levels across different fields, texture, LU, and other environmental factors became statistically more relevant than ρ _b. A modeled response surface for changes in ε with soil conditions may, in perspective, be useful for better-predicting gas transport in soil, both within and across fields.