Characterizing Macropores in Soil by Computed Tomography

Cross sections of a 203-mm diam. soil core taken from a site under Kentucky bluegrass (Poa pratensis L.) were scanned using x-ray computed tomography (CT) to determine if macropores such as cracks, earthworm holes and root channels could be distinguished and characterized. The core was physically sectioned at the same locations as the CT scans to verify the size and location of pores seen on the CT images. Macropores 1 mm and larger could be easily and quickly distinguished by the method. By manipulation of the scanner images, air-filled pores, roots and stones were identified within the soil matrix. A wet bulk density plus an air-filled macroporosity were calculated for scans. Prior to sectioning, a dye solution was ponded on the surface of the core and allowed to infiltrate to assess the continuity of pores through the core.