Soil Macroporosity Distribution and Trends in a No-till Plot using a Volume Computer Tomography Scanner

Soil macroporosity (voids with a diameter of 0-54 mm or more) was estimated in undisturbed soil columns obtained from eight I m by I m plots of a no-till field using image analysis, the soil samples having been scanned with a laboratory volume computer tomography (CT) scanner. Estimates of soil macroporosities in the A horizon, the B horizon and the entire field were found to be log-normally distributed. For the entire depth under consideration (0-400 mm), and the A horizon (0-200 mm), there was a significant decreasing trend in the soil macroporosity with depth. In the B horizon, the soil macroporosity showed neither a decreasing or increasing trend with depth. Using the Kolmogorov-Smirnov two-sample test, it was observed that both the physical and mechanical processes creating the soil macropores in the A and B horizons were completely different or if they were the same then the extent of the physical and mechanical processes involved in soil macropore formation were completely different e.g. the number of earthworms present in each horizon based on the availability of residue which acts as food and the number and type of plants roots available at each horizon.