Water Movement Through Pedal Soils II. Unsaturated Flow

Very high hydrodynamic dispersion, occurring during application of an unlimited dose of chloride‐traced water to 10 drained 55‐cm long columns with undisturbed pedal soils, was strongly reduced by a daily application of 1 cm of water. Dispersion in five columns with subangular blocky structures remained significantly higher than that measured in five columns with prismatic structures. Differences are explained by a hypothetical analysis of flow patterns in both types of structure. Application of a surface crust strongly reduced dispersion in the subangular blocky structures, even though the flow rate remained approximately 1 cm/day. This was attributed to lack of flow into the larger vertical pores extending through the columns. Pronounced differences in terms of hydrodynamic dispersion were found among two types of structures from three soil series, all with a silty clay loam texture. This demonstrates the potential usefulness of routine soil structure descriptions as a correlative tool for predicting certain aspects of physical behavior.