Soil Structure From a Soil-Air Physics Point of View: Gas Transport Parameters As Architectural and Functional Fingerprints.

An inspirational 75-yr anniversary paper in SSSAJ (Jury et al., 2012) looked at the future of soil physics platformed on the soil-water phase. The soil-air phase parameters and processes in combination with ongoing advances in porous media measurement and visualization technologies offer us additional keys to understand and quantify soil functional architecture and ecosystem services. 

Soil-air physics is therefore central to solve present-day challenges in land-based food, feed, and fuel production, and environmental, climate, and human health issues, including oxygen supply to crops, emission or uptake of greenhouse gases and surface applied pesticides, transport of health-affecting gases from soil to indoor air, and the design of optimal plant growth media. 

We suggest that rapid measurements and accurate, predictive modeling of the soil-gas diffusion and dispersion coefficients and soil-air permeability in combination with fast developments in X-ray CT scanning can enable groundbreaking progress in understanding soil functional pore and particle networks (architecture) towards predicting the mobility and fate of abiotic and biotic constituents in intact soil.  

We recommend that promising links between soil-air physics and environmental, civil, medical, and space engineering should be further embraced and explored. Four examples of pipeline inter-diciplinary research with large unsolved challenges will be highlighted: 

• Soil and climate: Modeling gas diffusivity and pore network tortuosity in intact soil - for improved vadose zone compartments in climate models (regional to global).
• Soil and health: Understanding gas mobility in compacted and fractured soil - for realistic worst case modeling of indoor air intrusion by radon and volatile chemicals.
• Smart porous media: Obtaining secure oxygen and substrate windows in optimal plant growth media - for applications on Earth and in Space (under reduced gravity).
• Seeing into soil: Fingerprinting and quantifying functional soil architecture by linking gas transport measurements with porous media visualization across scales.