A review of the changes in the soil pore system due to soil deformation: A hydrodynamic perspective

Compaction and shearing, as well as the rearrangement of soil aggregates and clods due to shrinkage, among other processes, can strongly affect the pore geometry of agricultural soils. These soil structural changes directly affect soil water movement by altering the hydraulic properties that are commonly described by the soil water retention curve (WRC) and the unsaturated hydraulic conductivity function (HCF). This review focuses on recent advances in the understanding and evaluation of changes in hydraulic functions in relation to compacted soil. The development of hydromechanical models due to recent advances with more sophisticated methods enables quantification of the effects of compaction on the hydraulic conductivity functions at the pore scale of aggregated soil. However, it remains unclear how to up-scale the dynamic, in terms of inter-aggregate pore models, into the continuum-scale dual-porosity models in the form of effective parameters, particularly regarding effective hydraulic properties for the preferential flow domain. While hydromechanical models fail to describe water flow and hydraulic conductivity at the relevant scales and water saturation ranges, the continuum-based flow models rely on effective parameters that are mainly empirical or are based on fitting model results to data. Input data usually do not address temporal changes in the arrangement of aggregates induced by soil compaction and shrinkage. This review presents a concept that summarizes the changes in structural and textural porosity upon compaction. It suggests focusing on the extension of existing hydraulic and hydromechanical models to include the pore structural changes that account for the movement and rearrangement of soil aggregates and the resulting changes in the soil hydraulic properties which basically manifest the effects of shearing and compaction on water flow. (C) 2011 Elsevier B.V. All rights reserved.