Soil Gas Diffusivity, Air‐Filled Porosity, and Pore Continuity: Land Use and Spatial Patterns

Abstract

Core Ideas Soil gas transport variables were greater in pasture than crop systems. Gas transport variables exhibited high spatial variation with higher CVs in the crop. Spatial variability of Ds/D0 was structured at all selected matric potentials. Ds/D0 revealed stronger spatial dependence in the crop and longer correlation in pasture. Spatial correlation length of Ds/D0 in the crop was controlled by soil water status. Soil gas diffusivity and air‐filled porosity are important soil variables indicating soil structure and aeration. Land use influences these soil gas transport variables, but their spatial patterns have not been sufficiently investigated. This study evaluated how land use affected soil gas diffusivity, air‐filled porosity, and pore continuity and quantified the spatial patterns of these soil gas transport variables in crop and pasture systems. Soil gas diffusivity was measured with a gas diffusion chamber as a function of air‐filled porosity in 60 soil cores taken from the two land‐use systems. Soil gas diffusivity, air‐filled porosity, and pore continuity were larger in the pasture than the crop system, indicating better soil aeration and a better developed soil structure, as observed under pasture relative to the crop system. Soil gas transport variables exhibited high spatial variability in both land‐use systems, with smaller CVs in the pasture than the crop system. Large spatial variability reflects the complexity of pore system organization at the sample scale and the possibility that the representative elementary volume was not captured at the sampling scale. Geostatistical analysis showed unique structured variability of these soil gas transport variables at the field scale, with longer correlation lengths in the pasture system and stronger spatial dependence in the crop system for soil gas diffusivity. The spatial patterns of soil gas transport variables and the influence of land use should be considered for experimental design and predictions of soil gas diffusivity.