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Short course: On the physical basis to understand the dynamics of soil hydraulic properties (co-organized)
Convener: Antonio Coppola  | Co-Convener: Horst H. Gerke 
Mon, 13 Apr, 13:30–15:15

It has frequently been reported that soil physical and hydrological properties are changing in time. This is mainly because the geometry of the soil porous system is dynamically changing in response to boundary conditions and continuous modifications of the physical soil environment. These changes become obvious, for example, in shrinking/swelling porous media. Most of the natural dynamics of soil porous system and the related hydraulic properties come from shrink-swell deformation processes in soils.
All the soils are more or less naturally undergoing deformation. Because of deformation, soils should mostly be treated as dynamic dual permeability /dual porosity systems, with complex interaction between the pore systems.
There are consolidated physically-based approaches now that can deal with water flow and solute transport accounting for the dynamic of the dual-pore-system and related hydraulic properties.
And yet, quantitative understanding of the pore-systems dynamic effects on the description and prediction of flow and transport phenomena or water and element budgets of soil ecosystems is still relatively limited.
This is mostly because of the difficulty in characterizing the hydrological behavior of the dual system. For large-scale hydrological predictions, pedotransfer functions (PTF) have been frequently used as a surrogate for hydraulic properties. Unfortunately, they are mostly empirically-based and not able to consider time-changes in the porous medium due to the natural dynamics of the pore systems.

Physically-based modeling of the mechanisms inducing deformation of the soil pore systems seems to provide a realistic basis to understand the retention and movement of water and solutes in soil.
We know now a lot on the dynamic (and hysteretic) behavior of the pore systems at the microscopic and clod scale. Many efforts have also been carried out to characterize the soil aggregate and biopore surfaces and their effects on the exchange in two-region flow and transport models. This may allow now linking physically the dynamics of the soil hydraulic properties to the dynamics of the porous system geometry by taking into account the shrinkage/swelling dynamics of the porous medium. As much of the knowledge is still confined mostly to the micro-scale (pore-clod scale), the challenge is how we can/should upscale the micro-scale knowledge to representative elementary volumes as a necessity for applications of the results to the solution of practical problems at applicative scales.
With these premises, the short course mainly aims at stimulating discussions and further model developments for soil hydraulic functions under dynamic deformation of the soil porous system based on the current knowledge on the actual morphology of the soil porous system and on deterministic relations colloidal constituents-water regimes.
The main points that will be presented in more details will be:
‒ Deformation described by quasi-completely pore-scale/clod-scale physical approach;
‒ Some present limitations in soil physics and in the "pedotransfer" approach;
‒ The nature of soil structure and soil porosity (dual porosity and swelling system versus) and the contradictions with approaches in soil physics;
‒ How the pore systems and their dynamics can be assessed with shrinkage analysis: theoretical and technical parts;
‒ How far is this validated or not;
‒ Examples of spatial and time variations of soil physical properties and potential for future soil physical research;
‒ Structural heterogeneity at the clod scale: Characterization of soil aggregate and biopore surfaces and their usage for parameterization of two-region flow and transport models

Pascal Boivin, University of Applied Sciences of Western Switzerland (HES-SO- Genève);

Horst H. Gerke, Institute of Soil Landscape Research,
Leibniz Centre for Agricultural Landscape Research (ZALF), Müncheberg, Germany;

Antonio Coppola, Dept. SAFE, Soil Hydrology Section, University of Basilicata, Italy