We introduce the “Soil is A-W-S-O-M” system, in the form of Air, Water, Solids, and its content of Organic Matter, as the main control of soil-gas diffusivity as a function of soil-air content. Focus is therefore on the separate and combined effects of (i) soil moisture, (ii) texture, (iii) compaction, (iv) structure including aggregation (bimodal behavior), and (v) organic matter.

     We revisit soil-gas diffusivity data covering both natural soil ecosystems and techno-soils, including cultivated land, forest soils, peat land, urban soils, final soil covers for municipal waste deposits, and optimized growth media. Based on this, we suggest a hierarchy of recommended, predictive gas diffusivity models depending on available input parameters.

     In perspective, we discuss model use in regard to quantifying and mapping gas fate and emission processes across scales. We briefly look ahead to some future challenges for soil-air physics including upscale of gas exchange predictions to Earth land area, and how climate and soil management changes may affect regulated gas diffusion, uptake, and emissions from soil.