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

Abstract

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 (kf), and the air permeability (ka) were measured. The air-filled porosity (ε3) was determined, and pore-continuity indices (ka/εa, ka/ εa2, N) and blocked porosities (εb) were derived from the relationship between ka and εa. 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. © 2006 Wiley-VCH Verlag GmbH & Co. KGaA.