Soil aggregate size distributions using X-ray images

A procedure for measuring the size distribution of soil aggregates with X-ray computed tomography (CT) was proposed and evaluated with respect to accuracy and feasibility of determining significant differences among tillage plots. Results indicate that characteristic geometric description of soil aggregates from scanned images, corrected using stereological approaches for a convex solid, is consistent with values obtained with sieving. CT-measured maximum and minimum apparent diameter values were 0.7 to 0.9 times the caliper-based values for specific clods, with R-2 values of 0.8 to 0.9. The ratio of the CT based to the sieve based values were as expected for a range of common convex solids. The geometric mean diameter (GMD) of soil aggregates predicted by rotary sieving and CT scanning are somewhat lower in magnitude and varied by plot, suggesting that rotary sieving process may have disrupted aggregates to varying extents across plots. Usage of the CT-based GMD values versus the rotary sieve-based GMD values resulted in identical determinations of relative differences among the respective GMDs from tillage plots. CT-based GMD values were obtained quickly since CT scanning avoids many time consuming sample preparation steps necessary for rotary sieve analysis.