Special Section: Frontiers of Hydropedology in Vadose Zone Research
Marcus Hardie* Richard Doyle William Cotching Greg Holz Shaun Lisson
Hydropedology and Preferential Flow in the Tasmanian TextureContrast Soils The two-way interaction between soil morphology and the processes governing soil water movement were investigated for a range of texture-contrast soil profiles. The texture-contrast soils consisted of a seasonally water-repellent sandy loam A1 horizon over a bleached silica-cemented A2e horizon and a mottled vertic clay subsoil. Differences in soil morphology and structure among sites had little influence on the proportion of soil that participated in infiltration or the maximum depth of infiltration; however, differences in subsoil structure influenced the processes by which water infiltrated and was stored within the B2 horizons. The occurrence of preferential flow was largely controlled by the effects of antecedent soil moisture content on water repellence in the A1 horizon, silica bridging in the A2e horizon, and clay shrinkage in the B2 horizons. Under dry soil conditions, infiltration resulted from up to five different forms of preferential flow. When soils were near field capacity, most forms of preferential flow ceased; however, wetting front instability and lateral flow developed in the A1 horizon. Preferential flows are not thought to have contributed to the pedogenesis of the texture-contrast soils. Development of the contrasting soil texture horizons, sand infills, and bleached A2e horizons developed before and independently of the observed preferential flow processes in which reworked aeolian sands buried previously developed clay columns. Abbreviations: CEC, cation exchange capacity; EC, electrical conductivity; ESP, exchangeable sodium percentage; WDPT, water drop penetration time; WEP, water-entry potential.
Infiltration into the texture-contrast soils was largely governed by the effects of antecedent soil moisture content on water repellence, silica bridging, and clay shrinkage. Differences in soil morphology had a relatively minor influence on infiltration. The contrasting horizon textures were thought to have developed prior to and independently of the observed preferential flows. M. Hardie, R. Doyle, G. Holz, and S. Lisson, Tasmanian Institute of Agriculture, Hobart, Tasmania 7001, Australia; M. Hardie and R. Doyle, School of Agricultural Science, Univ. of Tasmania, Sandy Bay, Tasmania 7001, Australia; W. Cotching, Tasmanian Institute of Agriculture, Univ. of Tasmania, Burnie, Tasmania, Australia; and S. Lisson, CSIRO Ecosystems Sciences, Univ. of Tasmania, Hobart, Tasmania 7001, Australia. *Corresponding author (
[email protected]). Vadose Zone J. doi:10.2136/vzj2013.03.0051 Received 10 June 2013.
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Hydropedology is an emerging field of science in which traditional disciplines of pedology, hydrology, and geomorphology are integrated to better understand the two-way relationship between soil morphology and the processes governing soil water movement (Lin, 2011). The hydropedology paradigm seeks to address two fundamental questions: (i) how does soil morphology and stratigraphy exert first-order control on hydrologic processes, biogeochemical dynamics, and ecological functions, and (ii) how do hydrologic processes influence soil genesis, evolution, variability, and function across space and time (Lin, 2012)? The Australian soil classification describes texture-contrast soils as having a clear, abrupt or sharp boundary between the B2t and overlying horizons in which the clay content immediately below the boundary is at least twice that of the overlying layer if it has
