Direction-dependent behaviour of hydraulic and mechanical properties in structured soils under conventional and conservation tillage

Dorner, J. and Horn, Rainer (2009) Direction-dependent behaviour of hydraulic and mechanical properties in structured soils under conventional and conservation tillage Soil & Tillage Research, 102 (2). pp. 225-232.

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The development of soil structure units with defined forms and dimensions (e.g. platy by soil compaction or prismatic up to subangular-blocky by swelling-shrinkage processes) can lead to direction-dependent behaviour of mechanical and hydraulic properties. However, little research has investigated direction-dependent behaviour directly. Undisturbed samples were collected at different horizons and orientations (vertical and horizontal) of Stagnic Luvisols derived from glacial till (Weichselian moraine region in Northern Germany). A direct shear test determined the cohesion (c) and the angle of internal friction (phi). The water retention curve (WRC), the saturated hydraulic conductivity (k(s)) and the air permeability (k(a)) were also measured. The air-filled porosity (epsilon(a)) was determined and pore continuity indices (N) and blocked porosities (epsilon(b)) were derived from the relationship between k(a) and epsilon(a).Although the pore volume as a scalar is isotrop, the saturated hydraulic conductivity and air permeability can be anisotropic. In the seedbed (SB) and plough pan (PP) of conventionally managed soils the effective porosity is non-direction-de pendent, however, differences in k(s) as a function of sampling direction can reach one order of magnitude in PP (k(s)h > k(s)v). The shear strength parameters do not present a significant anisotropy, although, a pronounced spatial orientation of soil aggregates (e.g. induced by soil compaction in a plough pan) lead to direction-dependent shear strength (by sigma(n): 10 kPa, sigma(t)v: 12 kPa and sigma(t)h: 19 kPa). This behaviour was especially observed in pore continuity indices (e.g. vertical and horizontal oriented aggregates observed in Bvg and PP presented epsilon V-b < epsilon(b)h and epsilon V-b > epsilon(b)h, respectively) showing that the identification of soil structure can be used as the flrst parameter to estimate if hydraulic properties present a direction-dependent behaviour at the scale of the soil horizon, which is relevant in modelling transport processes. (C) 2008 Elsevier B.V. All rights reserved.

Document Type: Article
Keywords: soil structureanisotropy hydraulic conductivity air permeability shear strength anisotropy conductivity macroporosity continuity strength gas
Research affiliation: ?? agrar ??
OceanRep > The Future Ocean - Cluster of Excellence
Refereed: Yes
ISSN: 0167-1987
Projects: Future Ocean
Date Deposited: 11 Feb 2011 12:16
Last Modified: 05 Sep 2016 12:15

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