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, rho(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 (epsilon) and soil-structure changes within and across sites in Greenland and Denmark. We analyzed comprehensive data sets of epsilon, 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 epsilon as a function of rho(b) (H-model). The ratio of k(a) to D-p/D-o served as a soil-structure index (omega); the latter significantly correlated to TUI. The Greenlandic pasture soils did not show signs of well-developed soil structure (low omega-values), whereas low H-values suggested the soils were mechanically robust compared to similar-textured cultivated soils. The soil-air characteristic curve (epsilon vs. pF) was parameterized, and the moisture control parameter was accurately predicted by TUI and LU (R-2 = .95). Overall, the rho(b) was found to control the air-phase functions within a field. However, considering changes in epsilon-levels across different fields, texture, LU, and other environmental factors became statistically more relevant than rho(b). A modeled response surface for changes in epsilon with soil conditions may, in perspective, be useful for better-predicting gas transport in soil, both within and across fields.

Automated summary

This study aimed to identify and compare the main factors affecting air-filled porosity and soil structure changes in Greenland and Denmark. It found that changes in texture, land use, and other environmental factors were more statistically relevant than soil bulk density in controlling air-phase functions within a field. A modeled response surface for changes in air-filled porosity with soil conditions may be useful for predicting gas transport in soil.