Applying X-ray CT to measure macropore diameters in undisturbed soil cores

Abstract

X-ray CT data are used to quantify macropore hole perimeters, equivalent hole diameters and hole porosities in undisturbed soil cores from the same soil taken from a forest and from a field in perennial grasses. This analysis demonstrates the capabilities of X-ray CT as a tool to rapidly and nondestructively quantify macropore characteristics. The data are analyzed using an algorithm previously developed by the authors. The differences in macropore characteristics between the forest and field are compared. Only those macropores with computed equivalent diameters greater than 0.5 mm were evaluated. The most holes were found in the 0.5 to 1.0-mm-diameter range. The mean diameter was 19% larger in the field cores than in the forest cores, but the field cores had 21% fewer total number of holes. This resulted in approximately equal computed values for hole porosity for the forest and field cores. However, the hole porosity due to hole diameters of 2.0 mm and less was 56% greater in the forest cores than the field cores. Frequency distributions for CT numbers, proportional to soil bulk density, were evaluated. Both forest and field cores had highly skewed frequency distributions due to the presence of the macropores. The field core distribution was more skewed than for the forest cores.