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Effects of Aggregate Skins on Flow and Transport in Structured Soil

Published by the American Society of Agricultural and Biological Engineers, St. Joseph, Michigan

Citation:  Pp. 293-296 in Preferential Flow, Water Movement and Chemical Transport in the Environment, Proc. 2nd Int. Symp. (3-5 January 2001, Honolulu, Hawaii, USA), eds. D. D. Bosch and K. W. King. St. Joseph, Michigan: ASAE  701P0006.(doi:10.13031/2013.2100)
Authors:   Horst H. Gerke, Chittaranjan Ray, and Tomas Vogel
Keywords:   Preferential flow, dual-permeability model, mass transfer, sensitivity analysis, soil aggregate skins

Preferential flow may not only be controlled by differences in hydraulic properties between the intra- (soil matrix) and inter-aggregate (fracture) pore system but also by the mass transfer characteristics. Clayey skins, frequently found on soil aggregates in argillic soil horizons, could be responsible for restricting mass transfer rates and thereby increasing preferential flow within the inter-aggregate pore network. The objective of this study was to analyze the sensitivity of the hydraulic conductivity and solute diffusivity of the matrix/fracture interface. The simulated scenario used hydraulic properties from a tile-drained clay-loam glacial till soil profile and considered an initially wet and solute-free soil profile. A fertilizer application, comparable to 100 kg nitrate-N/ha, and two rainfall events totaling 65 mm, were simulated over a period of 30 days. The simulation results indicated that small values of the hydraulic conductivity and the diffusivity of the matrix/fracture interface relative to those of the soil matrix, lead to highest water and solute leaching rates and deepest nitrate penetration in the profile. First experimental data on the hydraulic properties of clayey aggregate skins show values in same order of magnitude used in the sensitivity studies. The results demonstrate the importance of considering a possible skin-induced conductivity and diffusivity reduction which can control the generation of local nonequilibrium in pressure head and solute concentration and preferential flow in aggregated soils.

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