Soil bulk density and porosity connecting macro- and micro-scales through geometry

Robinson, D.A. ORCID: https://orcid.org/0000-0001-7290-4867; Friedman, S.P.; Thomas, A. ORCID: https://orcid.org/0000-0002-4929-7285; Hirmas, D.; Sullivan, P.L.; Nemes, A.. 2025 Soil bulk density and porosity connecting macro- and micro-scales through geometry. Earth-Science Reviews, 268, 105173. 10.1016/j.earscirev.2025.105173

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Official URL: https://doi.org/10.1016/j.earscirev.2025.105173

Abstract/Summary

Soil bulk density (BD) is a macroscopic indicator frequently used to infer the soils' pore system, a fundamental attribute of terrestrial environments that significantly affects processes such as infiltration, water retention and plant root development. Additionally, BD is essential for assessing the storage of various materials in soils and sediments, including carbon and nutrients. High bulk density, often a consequence of soil compaction, represents a form of soil degradation that diminishes the soil's functional capacity. Therefore, effective management of soil BD is crucial for improving agricultural yields, safeguarding ecosystem services, preventing degradation, and preserving the overall integrity of the Earth's system. This review synthesizes recent research on the packing behavior of granular materials to clarify the emergent property of soil BD. The findings yield an empirical model that links packing fraction to the shape and size ratio of particles. The results demonstrate that the model accurately captures the frequently observed exponential decrease in soil BD with increasing soil organic matter (SOM) content. While it is widely recognized that particle density influences BD, the analysis indicates that grain shape exerts a considerable effect, followed by the particle size ratio in granular media. The insights from this study aim to transform the perception of BD from a static notion to one that acknowledges how changes in the morphology of soil constituents, driven by factors such as root growth and decomposition, can result in variations in BD. As a result, BD may become increasingly sensitive to feedback from climate and land use changes as the geometry of SOM evolves.

Item Type:	Publication - Article
Digital Object Identifier (DOI):	10.1016/j.earscirev.2025.105173
UKCEH and CEH Sections/Science Areas:	Environmental Pressures and Responses (2025-)
ISSN:	0012-8252
Additional Information. Not used in RCUK Gateway to Research.:	Open Access paper - full text available via Official URL link.
Additional Keywords:	grain, packing, shape, soil, granular media, particle size distribution
NORA Subject Terms:	Agriculture and Soil Science
Date made live:	17 Jun 2025 07:46 +0 (UTC)
URI:	https://nora.nerc.ac.uk/id/eprint/539601

Item Type:

Publication - Article

Digital Object Identifier (DOI):

10.1016/j.earscirev.2025.105173

UKCEH and CEH Sections/Science Areas:

Environmental Pressures and Responses (2025-)

ISSN:

0012-8252

Additional Information. Not used in RCUK Gateway to Research.:

Open Access paper - full text available via Official URL link.

Additional Keywords:

grain, packing, shape, soil, granular media, particle size distribution