Anisotropy of pore functions in structured Stagnic Luvisols in the Weichselian moraine region in N Germany

In order to determine if soil hydraulic properties present a direction‐dependent behavior, undisturbed samples were collected at different horizons and orientations (vertical, diagonal [45°], and horizontal) in structured soils in the Weichselian moraine region in northern Germany. The water‐retention curve (WRC), the saturated hydraulic conductivity (k f ), and the air permeability (k a ) were measured. The air‐filled porosity (ϵ a ) was determined, and pore‐continuity indices (k a /ϵ a , k a /ϵ a 2 , N) and blocked porosities (ϵ b ) were derived from the relationship between k a and ϵ a . The development of soil structures with defined forms and dimensions ( e.g. , platy by soil compaction or prismatic up to subangular‐blocky by swelling–shrinkage processes) and the presence of biopores can induce a direction‐dependent behavior of pore functions. Although the pore volume as a scalar is isotropic, the saturated hydraulic conductivity and air permeability (as a function of air‐filled porosity) can be anisotropic. This behavior was observed in pore‐continuity indices showing that the identification of soil structure can be used as a first parameter to estimate if hydraulic properties present a direction‐dependent behavior at the scale of the soil horizon.