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High-Resolution Bulk Density Images, Using Calibrated X-ray Radiography of Impregnated Soil Slices

Département Agronomie-Environnement, Institut National Agronomique Paris-Grignon, 78850 Thiverval-Grignon, France

C. J. Moran

Division of Soils, G.P. Box 639, Canberra, ACT 2601, Australia

*Corresponding author (lmb{at}lacan.grignon.inra.fr).

ABSTRACT

Bulk density of undisturbed soil samples can be measured using computed tomography (CT) techniques with a spatial resolution of about 1 mm. However, this technique may not be readily accessible. On the other hand, x-ray radiographs have only been considered as qualitative images to describe morphological features. A calibration procedure was set up to generate two-dimensional, high-resolution bulk density images from x-ray radiographs made with a conventional x-ray diffraction apparatus. Test bricks were made to assess the accuracy of the method. Slices of impregnated soil samples were made using hardsetting seedbeds that had been gamma scanned at 5-mm depth increments in a previous study. The calibration procedure involved three stages: (i) calibration of the image grey levels in terms of glass thickness using a staircase made from glass cover slips, (ii) measurement of ratio between the soil and resin mass attenuation coefficients and the glass mass attenuation coefficient, using compacted bricks of known thickness and bulk density, and (iii) image correction accounting for the heterogeneity of the irradiation field. The procedure was simple, rapid, and the equipment was easily accessible. The accuracy of the bulk density determination was good (mean relative error 0.015). The bulk density images showed a good spatial resolution, so that many structural details could be observed. The depth functions were consistent with both the global shrinkage and the gamma probe data previously obtained. The suggested method would be easily applied to the new fuzzy set approach of soil structure, which requires generation of bulk density images. Also, it would be an invaluable tool for studies requiring high-resolution bulk density measurement, such as studies on soil surface crusts.

Received for publication November 25, 1996.

This article has been cited by other articles:

				B. Augeard, L. M. Bresson, S. Assouline, C. Kao, and M. Vauclin Dynamics of Soil Surface Bulk Density: Role of Water Table Elevation and Rainfall Duration Soil Sci. Soc. Am. J., January 25, 2008; 72(2): 412 - 423. [Abstract] [Full Text] [PDF]

				L. M. Bresson, C. J. Moran, and S. Assouline Use of Bulk Density Profiles from X-Radiography to Examine Structural Crust Models Soil Sci. Soc. Am. J., July 1, 2004; 68(4): 1169 - 1176. [Abstract] [Full Text] [PDF]