Submicroscopic measurements of tracer distribution related to surface features of soil aggregates

Previous studies suggested that surface features of soil aggregates, such as clay coatings and slickenside surfaces, could serve as slowly permeable barriers for tracer movement into soil aggregates. The objective of the research was to identify the transport of solutes at the submicroscopic scale as related to the surface aggregate features in two Vertisols and an Alfisol. Solute flow through structural interfaces in these soils was estimated by identifying visual distribution of Brilliant Blue FCF and the distribution of anionic tracer (Br) by means of electron microprobe analysis. Brilliant Blue FCF moved through the surface of pedofeatures into subjacent soil matrix to the distances of 0.5–1 mm. In contrast to the Brilliant Blue FCF dye, Br moved across structural interfaces 1 to 4 cm into the aggregate interior. These results suggest that the surfaces of structural features in these soils did not act as significant barriers to Br penetration into the soil matrix.