Bimodal soil pore structure investigated by a combined soil water retention curve and X-ray Computed Tomography approach

Well-structured soils are generally considered to have bimodal pore structure, including textural pores between soil particles and structural pores between soil aggregates. Bimodal pore structure has previously been inferred indirectly from the soil water retention curve (SWRC) but our understanding...

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Main Authors:	Zhou, Hu, Mooney, Sacha J., Peng, Xinhua
Format:	Article
Language:	English
Published:	Soil Science Society of America 2017
Online Access:	http://eprints.nottingham.ac.uk/44581/ http://eprints.nottingham.ac.uk/44581/ http://eprints.nottingham.ac.uk/44581/ http://eprints.nottingham.ac.uk/44581/1/MS-swrc-20161019%20Mooney.pdf

id	nottingham-44581
recordtype	eprints
spelling	nottingham-445812018-01-30T19:30:30Z http://eprints.nottingham.ac.uk/44581/ Bimodal soil pore structure investigated by a combined soil water retention curve and X-ray Computed Tomography approach Zhou, Hu Mooney, Sacha J. Peng, Xinhua Well-structured soils are generally considered to have bimodal pore structure, including textural pores between soil particles and structural pores between soil aggregates. Bimodal pore structure has previously been inferred indirectly from the soil water retention curve (SWRC) but our understanding of the precise 3-D pore geometry that regulates this curve is limited. The objective of this study was to investigate the bimodal pore structure of a paddy soil under different fertilization regimes using both SWRC and X-ray micro-Computed Tomography (micro-CT), an imaging approach with the aim of comparing the two methods. Undisturbed soil aggregates and soil cores were collected from the surface layer of a long-term unfertilized control (CK), inorganically fertilized (NPK), and organically and inorganically fertilized (NPKOM) paddy soils. The aggregates and cores were scanned using micro-CT and pore structure analyzed. The SWRCs were measured on the same CT-scanned soil cores. Three widely used unimodal models, three bimodal models, and one trimodal model were evaluated for their fit to the SWRC and to derive soil pore size distribution (PSD). Results showed the SWRC of the paddy soil were best fitted with the bimodal lognormal (BLN) and double-exponential (DE) models, with the derived PSD showing distinct bimodality. The micro-CT images revealed the hierarchy structure of the paddy soil and a distinct bimodal pattern in the PSDs. The structural porosities from BLN, DE models and from CT imaging are consistent, and all correlated with the natural logarithm of saturated hydraulic conductivity. Long-term application of NPKOM increased structural porosity though no changes were recorded in the textural porosity compared with NPK and CK treatment, while the latter two showed a near identical pore structure. The results of this study showed the consistence of the SWRC and imaging method in studying soil pore structure and supported the use of bimodal SWRC models to investigate the pore structure of the well-structured paddy soil. Soil Science Society of America 2017-11-02 Article PeerReviewed application/pdf en http://eprints.nottingham.ac.uk/44581/1/MS-swrc-20161019%20Mooney.pdf Zhou, Hu and Mooney, Sacha J. and Peng, Xinhua (2017) Bimodal soil pore structure investigated by a combined soil water retention curve and X-ray Computed Tomography approach. Soil Science Society of America Journal, 81 (6). pp. 1270-1278. ISSN 1435-0661 https://dl.sciencesocieties.org/publications/sssaj/abstracts/0/0/sssaj2016.10.0338 doi:10.2136/sssaj2016.10.0338 doi:10.2136/sssaj2016.10.0338
repository_type	Digital Repository
institution_category	Local University
institution	University of Nottingham Malaysia Campus
building	Nottingham Research Data Repository
collection	Online Access
language	English
description	Well-structured soils are generally considered to have bimodal pore structure, including textural pores between soil particles and structural pores between soil aggregates. Bimodal pore structure has previously been inferred indirectly from the soil water retention curve (SWRC) but our understanding of the precise 3-D pore geometry that regulates this curve is limited. The objective of this study was to investigate the bimodal pore structure of a paddy soil under different fertilization regimes using both SWRC and X-ray micro-Computed Tomography (micro-CT), an imaging approach with the aim of comparing the two methods. Undisturbed soil aggregates and soil cores were collected from the surface layer of a long-term unfertilized control (CK), inorganically fertilized (NPK), and organically and inorganically fertilized (NPKOM) paddy soils. The aggregates and cores were scanned using micro-CT and pore structure analyzed. The SWRCs were measured on the same CT-scanned soil cores. Three widely used unimodal models, three bimodal models, and one trimodal model were evaluated for their fit to the SWRC and to derive soil pore size distribution (PSD). Results showed the SWRC of the paddy soil were best fitted with the bimodal lognormal (BLN) and double-exponential (DE) models, with the derived PSD showing distinct bimodality. The micro-CT images revealed the hierarchy structure of the paddy soil and a distinct bimodal pattern in the PSDs. The structural porosities from BLN, DE models and from CT imaging are consistent, and all correlated with the natural logarithm of saturated hydraulic conductivity. Long-term application of NPKOM increased structural porosity though no changes were recorded in the textural porosity compared with NPK and CK treatment, while the latter two showed a near identical pore structure. The results of this study showed the consistence of the SWRC and imaging method in studying soil pore structure and supported the use of bimodal SWRC models to investigate the pore structure of the well-structured paddy soil.
format	Article
author	Zhou, Hu Mooney, Sacha J. Peng, Xinhua
spellingShingle	Zhou, Hu Mooney, Sacha J. Peng, Xinhua Bimodal soil pore structure investigated by a combined soil water retention curve and X-ray Computed Tomography approach
author_facet	Zhou, Hu Mooney, Sacha J. Peng, Xinhua
author_sort	Zhou, Hu
title	Bimodal soil pore structure investigated by a combined soil water retention curve and X-ray Computed Tomography approach
title_short	Bimodal soil pore structure investigated by a combined soil water retention curve and X-ray Computed Tomography approach
title_full	Bimodal soil pore structure investigated by a combined soil water retention curve and X-ray Computed Tomography approach
title_fullStr	Bimodal soil pore structure investigated by a combined soil water retention curve and X-ray Computed Tomography approach
title_full_unstemmed	Bimodal soil pore structure investigated by a combined soil water retention curve and X-ray Computed Tomography approach
title_sort	bimodal soil pore structure investigated by a combined soil water retention curve and x-ray computed tomography approach
publisher	Soil Science Society of America
publishDate	2017
url	http://eprints.nottingham.ac.uk/44581/ http://eprints.nottingham.ac.uk/44581/ http://eprints.nottingham.ac.uk/44581/ http://eprints.nottingham.ac.uk/44581/1/MS-swrc-20161019%20Mooney.pdf
first_indexed	2018-09-06T13:34:38Z
last_indexed	2018-09-06T13:34:38Z
_version_	1610865315860709376

Bimodal soil pore structure investigated by a combined soil water retention curve and X-ray Computed Tomography approach

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