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(1995-1999/ R
esearch Team: J. Perret, S. Prasher, A. Kantzas)



The role of macropores in soil and water processes has motivated many researchers to describe their sizes and shapes.  Several approaches have been developed to characterize macroporosity, such as the use of tension infiltrometers, breakthrough curve techniques, image-analysis of sections of soils and even X-ray CAT scanning. Until now, efforts to describe macropores in quantitative terms have been concentrated on their 2-D geometry.  The objective of this study was to quantify, in a non-destructive manner, 3-D properties of soil macropores in four large (800 mm x 77 mm diameter) undisturbed soil columns taken from a field site at the Macdonald Campus of McGill University in Ste-Anne-de-Bellevue, Quebec.  The main characteristics of the geometry and topology of macropore networks were determined using X-ray CAT scanning and three-dimensional reconstruction techniques.  Our results suggested that the numerical density of macropores varies between 13,421 to 23,562 networks per cubic meter of the sandy loam soil.  It was found that the majority of the macropore networks had a length of 40 mm, a volume of 60 mm3 and a wall area of 175 mm2. It was found that the greater the length of networks, the greater the hydraulic radius.



The inclination of the networks ranged from vertical to an angle of about 55 degrees from vertical. The overall tendency of the distributions of the inclination of networks suggested that the smaller the inclination, the greater the number of macropores.Results for tortuosity indicated that most macropore networks had a three-dimensional tortuous length 15% greater than the distance between its extremities.  More than 60% of the networks were made up of 4 branches.  For Column 1, it was found that 82% of the networks had zero connectivity.  (Click here for more info)



2000 Johan Perret