Using CAT scanning techniques to relate macropore distribution and connectivity to hydraulic conductivity

The hydraulic properties of fourteen soil cores of 300 millimetres in length and 15 millimetres in diameter; extracted from the Ballentrae property in New Zealand, were measured to determine the effects of two earthworm species (A. longa and A. caliginosa) on soil structure and internal drainage. A Computer Assisted Tomography (CAT) Scanner was used to obtain internal images of the soil structure. An attempt is made here to investigate the relationship between physical measurements of hydraulic conductivity and macropore distribution and connectivity derived from the scanned images. Physical measurements of water flow were made at positive and negative supply potentials to progressively exclude different-sized macropores from the flow process. In this way, an assessment can be made of the contributing effect that various pore sizes have to rapid moisture transfers within the soil profile. The resulting information will aid in the understanding of how macropore networks can be created and manipulated using earthworms to improve the internal drainage of soils and reduce erosional effects of surface runoff