EVALUATION OF CONSTRUCTED AND NATURAL SOIL MACROPORES USING X-RAY COMPUTED-TOMOGRAPHY

Characterization of macropores (1-5 mm diam. holes) in undisturbed soils has been hindered due to the lack of an easy, noninvasive method. The recent development of X-ray computed tomography (CT) scanners may provide a technique for rapid, nondestructive analysis of macropores in undisturbed soil cores. Research was conducted to evaluate constructed and natural soil macropores using a Siemens DRH CT scanner. Undisturbed soil cores (76.4 × 76.4 mm) were removed from the A horizon of a Menfro silt loam (fine-silty, mixed, mesic Typic Hapludalf) soil of two adjacent sites under different management. One site had been under continuous cultivation and the other under natural forest. Additional soil cores were packed to selected soil densities using sieved soil material from the surface horizon of the Menfro silt loam soil. Constructed macropores were created by placing wires ranging from 0.5 to 5.0 mm diam. in the soil during packing and removing the wires prior to scanning. Bulk density, measured in 1 mm3 volumes, correlated well (r=0.97) with the size and location of the constructed macropores. Frequency distributions of bulk density measured in the undisturbed cores from the cultivated and forest sites were negatively skewed due to the low density within structural features of the cores. The mean skewness coefficients were found to be -0.28 and -0.37 for the cultivated and forest cores, respectively. Analysis of bulk densities measured in transects within the cores using autocorrelation and partial autocorrelation functions suggested that bulk density was autocorrelated at small distances and could be described by a first-order autoregressive system. Results indicate that CT has good potential as a technique for evaluating structural characteristics in soils. © 1990.