T. R. 2008. Application of X-ray computed tomography to soil science: A literature review. Can. J. Soil Sci. 88: 1Á20. The study of the spatial configuration of soil, in its complexity, requires an understanding of the interrelations and interactions between the diverse soil constituents, at various levels of organization. Investigations of the spatial arrangement of the mineral and organic components of soil have benefited from the development of techniques for structural analysis. X-ray computed tomography (CT) is a non-destructive and non-invasive technique that has been successfully used for three-dimensional (3D) examination of soil. Valuable information has been obtained by the application of CT for the description and quantitative measurements of soil structure elements, especially of soil pores and pore network features. In many studies, X-ray CT has been used to investigate the hydro-physical characteristics of the soil, in a functional and temporal manner. A dynamic approach has also been utilized in the evaluation of the biotic factor influence on soil. The analysis of soil solid phases, by X-ray CT, has been challenging due to the similar X-ray attenuation of different solid constituents. However, the use of multiple X-ray energy levels has facilitated the discrimination of minerals in soil. The aim of this review and synthesis is to offer a perspective on the major issues related to application of the technique, general attempted solutions and possible directions in the utilization of X-ray CT in soil research. Relevant scanning parameters, procedures for CT image reconstruction, algorithms for the quantification of soil characteristics and results are presented for each type of application.Key words: X-ray computed tomography, energy level, spatial resolution, segmentation, soil mineral and organic constituents, soil physical and hydro-physical properties, soil biota Taina, I. A., Heck, R. J. et Elliot, T. R. 2008. Application de la tomographie aux rayons X a`la science du sol : survol de la litte´rature. Can. J. Soil Sci. 88: 1Á20. Pour e´tudier la configuration spatiale du sol dans toute sa complexite´, il faut comprendre les relations et les interactions des fractions du sol a`diffe´rents niveaux d'organisation. Les recherches sur l'organisation spatiale des couches mine´rales et organiques du sol ont profite´du de´veloppement de techniques d'analyse structurale. La tomographie aux rayons X assiste´e par ordinateur (TXAO) est une technique non destructive et non invasive qu'on a applique´e avec succe`s a`l'analyse tridimensionnelle du sol. L'usage de la TXAO pour de´crire et quantifier les e´le´ments structuraux du sol, surtout les pores et les particularite´s de leurs re´seaux, a permis de glaner quelques pre´cieuses informations. Maintes e´tudes rapportent qu'on s'est servi de la TXAO pour pre´ciser les proprie´te´s hydrophysiques du sol sur le plan fonctionnel ou temporel. On a aussi recouru a`une approche dynamique pour e´valuer l'influence des facteurs biotiques sur le sol. L'analyse des p...

Porosity and void characteristics of two major Acrisols (Ferric Acrisol and a Ferri-Plinthic Acrisol) with contrasting pedogenic features from the humid forest zone of Ghana were studied by X-ray computed microtomography. Spatial variability of the porosity of the two Acrisols, as well as the volume of different classes of void size, shape, and orientation, was quantitatively determined. Variations in the void characteristics were interpreted in correlation with the pedogenic features of the two soils. The Ferri-Plinthic Acrisol, with more numerous roots, faunal burrows, and with smaller amounts of rock fragments than the Ferric Acrisol, exhibited a larger total pore volume. The greatest part of the pore volume in the two soils could be associated with the macrovoids class. There was a strong correlation between void size and shape. Regular voids corresponded in general to mesovoids of biogenic origin, especially in the surface horizons, whereas irregular and elongated voids were composed mostly of macrovoids. Void orientation was predominantly inclined, with the exception of the horizons where the root or fauna advancement was impeded by a dense subjacent horizon. Considering soil-vegetation relationships, the computed microtomography imagery showed that root development in the lower horizons of the Ferric Acrisol was probably impeded by Fe-Mn nodules; cultivation of Crotalaria juncea on this soil probably facilitated the root penetration in some of the denser zones within the profile. The Ferri-Plinthic Acrisol structure could be improved by the extensive root system of Chromolaena odorata, a self-established fast-growing perennial shrub. Management strategies of the two major soils need to take into account relevant information on pore distribution, morphology, and orientation.

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Computerized analysis of soil thin section imagery leads to quantitative estimation of various soil features and allows interpretation of soil properties in connection with soil genesis and evolution. Our objective was to assess an object‐oriented software (that was created especially for remote sensing) in the study of soil thin sections. The capabilities of this software were tested on three Orthic Humic Gleysols (Typic Humaquepts), profiles that have been thoroughly analyzed in the past by means of more traditional image analysis methods. The software utilizes a multiresolution segmentation function that enables the separation, at different levels of observation, of objects representing micromorphological features. Objects that corresponded to voids, coarse and fine fractions with variable compositions, and redoximorphic pedofeatures were distinguished and grouped in classes arranged in a hierarchical manner. Classification was based not only on object spectral values, but also on object shape characteristics, as well as class‐related features. Each designated class was evaluated quantitatively. Structural changes caused by agricultural practices were evidenced by image analysis in conjunction with micromorphological characterization. Relational and contextual data concerning Fe–Mn nodules and mottles were extracted and interpreted from the perspective of pedogenetic conditions.