Synchrotron microtomographic quantification of geometrical soil pore characteristics affected by compaction

Abstract

Abstract. Soil compaction degrades soil structure and affects water, heat, and gas exchange as well as root penetration and crop production. The objective of this study was to use X-ray computed microtomography (CMT) techniques to compare differences in geometrical soil pore parameters as influenced by compaction of two different aggregate size classes. Sieved (diameter < 2 mm and < 0.5 mm) and repacked (1.51 and 1.72 Mg m −3 ) Hamra soil cores of 5 by 5 mm (average porosities were 0.44 and 0.35) were imaged at 9.6 µm resolution at the Argonne Advanced Photon Source (synchrotron facility) using X-ray CMT. Images of 58.9 mm 3 volume were analyzed using 3-Dimensional Medial Axis (3-DMA) software. Geometrical characteristics of the spatial distributions of pore structures (pore radii, volume, connectivity, path length, and tortuosity) were numerically investigated. Results show that the coordination number (CN) distribution and path length (PL) measured from the medial axis were reasonably fit by exponential relationships P(CN) = 10 −CN/Co and P(PL) = 10 −PL/PLo , respectively, where Co and PLo are the corresponding characteristic constants. Compaction reduced porosity, average pore size, number of pores, and characteristic constants. The average pore radii (63.7 and 61 µm; p < 0.04), largest pore volume (1.58 and 0.58 mm 3 ; p = 0.06), number of pores (55 and 50; p = 0.09), and characteristic coordination number (3.74 and 3.94; p = 0.02) were significantly different between the low-density than the high-density treatment. Aggregate size also influenced measured geometrical pore parameters. This analytical technique provides a tool for assessing changes in soil pores that affect hydraulic properties and thereby provides information to assist in assessment of soil management systems.

Soil Compaction under Three Different Land Use Systems within the Semi-deciduous Agro-ecological Zone of Ghana

“…Low bulk density exhibited in the natural forest can be attributed to higher organic matter residues on the soil surface; adequate pore space [18] and il structure and drainage [15] as well as limited human impacts. In contrast, Islam and Weil [19] observed higher bulk density in a natural forest attributing it to land use changes, especially cultivation of deforested land rapidly diminishing soil quality leading to reduction of land productivity. Therefore, higher bulk densities will eventually reduce crop yield and restrict root penetration [13,22].…”

“…Therefore, higher bulk densities will eventually reduce crop yield and restrict root penetration [13,22]. Weil [19] observed higher bulk density in a natural forest attributing it to land use changes, especially cultivation of deforested land rapidly ty leading to reduction of land productivity. Therefore, higher bulk densities will eventually reduce crop yield and restrict root Volumetric soil moisture of three (3) land use systems at three depths 49.6…”

“…The core methods through laboratory and field surveys provided a good estimate of the impact of compaction on soil physical parameters, but some recent improvements soil parameters estimation provided by Reidy et al [18] capitalized on their oversights and used pedotransfer functions to estimate bulk densities per horizon based on known soil parameters. Also, Udawatta et al [19] used an interesting X-ray computed microtomography (CMT) method to analyze the influence of compaction on geometrical soil pore parameters. Their methodological approaches found that compaction significantly reduces soil pore properties which invariably affects hydraulic properties.…”

The Impact of Capillary Trapping of Air on Satiated Hydraulic Conductivity of Sands Interpreted by X-ray Microtomography

“…A frequently used imaging technique in porous media research is synchrotron-based X-ray tomography. Taking advantage of its high image resolution, it was often applied to obtain pore geometry properties [28][29][30], aggregate microstructures [31][32][33] and multi-phase flow observations [34,35]. Industrial X-ray scanners are also suited to collect detailed information on soil structure development [36,37] or gas bubbles distribution [38][39][40][41][42].…”

The environment qualities evaluation of a degraded area in recuperation and the drying process of a Brazilian soil using nonconventional methods at micrometric scale

“…This generates the possibility to investigate water into the soil at microscopy scale, in relation to time using X-ray microtomography. In general, experiments in this scale are possible with help of synchrotron radiation, showed in recent work by Udawatta et al (2015), which quantified the consequences of mechanical compaction over porous geometry of two classes of soil aggregates at 9.6 µm. Ma et al (2015) evaluated microstructure and stability of two Urtisol aggregates submitted to wetting and drying cycle at 3.7 µm of resolution.…”