Water and Chloride Movement Through Soil Columns Simulating Pedal Soils

Interpretation of dispersion phenomena in soils is complicated by many complex interactions within the highly heterogeneous pore system. Model experiments were therefore designed to investigate the specific effects on hydrodynamic dispersion of (i) vertically continuous macropores in different types of microstructure and (ii) different flow regimes. Two homogeneous microstructures were formed by mixing, puddling, and drying of sand and silty clay loam materials to sandy loam and clay loam textures. Small vertically continuous cylindrical pores were made in 30‐cm long columns that had a diameter of 10 cm to simulate macropores. Breakthrough curves, following a daily 0.5‐cm application of chloride solution, showed that identical macropores have different hydraulic functions in different soil materials. This intermittent flow resulted in much better displacement of untraced water in the more permeable sandy loam columns, but “immobile” water remained in both soils. Dispersion phenomena in both microstructures (which represented two “ideal” textural porosities) differed significantly when saturated flow was compared with flow through a crust. Implications for the physical interpretation of soil structure descriptions are discussed.