Soil structure development and preferential solute flow

Soil structure and preferential flow are thought to be highly related, but quantification of this relationship has remained problematic. A combination of experiments on two soils at local and field scale was used to study the relationships between the degree of structural development, saturated cond uctivities K-s, moisture release, breakthrough parameters, and observations of preferential flow at the field scale. The convection dispersion equatio n and mobile-immobile model were fitted to breakthrough curves, and flow ch annels were stained with dye. Well-developed structure was associated with high dispersivities, a high coefficient of variation of K-s, and low mobile water contents, low exchange coefficients, and a low dyed area. Field-scal e observations matched the differences in structure and preferential flow p arameters observed at the local scales. Local-scale preferential flow appea red to highly influence field-scale solute transport, indicating that this is an important local-scale process which is not dampened at the field scal e. A conceptual model of subsoil structural development was expanded with p hysical parameters matching the structural development stage to predict the likelihood of preferential flow on the basis of the saturation regime of t he horizon or pedon.