Influence of antecedent soil moisture on hydraulic conductivity in a series of texture‐contrast soils

Abstract

Abstract:Antecedent soil moisture significantly influenced the hydraulic conductivity of the A1, A2e and B21 horizons in a series of strong texture-contrast soils. Tension infiltration at six supply potentials demonstrated that in the A1 horizon, hydraulic conductivity was significantly lower in the 'wet' treatment than in the 'dry' treatment. However in the A2e horizon, micropore and mesopore hydraulic conductivity was lower in the 'dry' treatment than the 'wet' treatment, which was attributed to the precipitation of soluble amorphous silica. In the B21 horizon, desiccation of vertic clays resulted in the formation of shrinkage cracks which significantly increased near-saturated hydraulic conductivity and prevented the development of subsurface lateral flow in the 'dry' treatment. In the 'wet' treatment, the difference between the hydraulic conductivity of the A1 and B21 horizons was reduced; however, lateral flow still occurred in the A1 horizon due to difficulty displacing existing soil water further down the soil profile. Results demonstrate the need to account for temporal variation in soil porosity and hydraulic conductivity in soilwater model conceptualisation and parameterisation.

Hydropedology and Preferential Flow in the Tasmanian Texture‐Contrast Soils

“…When the soils were at moisture contents near field capacity, the vertical forms of preferential flow ceased (Hardie et al, 2011); however, wetting front instability and lateral flow developed in the A1 horizon [Fig. 5b(vii)] during the infiltration of new water due to difficultly displacing existing soil water from the A1 and A2e horizons into the B21 horizon following clay swelling (Hardie et al, 2012a, 2012d).…”

“…Despite the A2e horizon having a loamy sand texture and considerable evidence of leaching (pH in CaCl 2 <4.7, organic C <0.86%, bleached color), under dry soil conditions the near‐saturated hydraulic conductivity (matric potential ψ = −0.13 kPa) of the A2e horizon was significantly lower (5.7 mm h −1 ) than both the overlying A1 horizons (42.2 mm h −1 ) and the underlying B21 horizons (16.2 mm h −1 ) (Hardie et al, 2012d). Reduced hydraulic conductivity in the A2e horizon was attributed to the absence of large (>1.5‐mm) macropores and partial blockage of small mesopores and micropores by amorphous silica bridging (Chartres et al, 1990; Norton, 1994).…”

“…Reduced hydraulic conductivity in the A2e horizon was attributed to the absence of large (>1.5‐mm) macropores and partial blockage of small mesopores and micropores by amorphous silica bridging (Chartres et al, 1990; Norton, 1994). However, when the A2e horizon became saturated, the silica bridging returned to solution, which significantly increased the micropore and small mesopore hydraulic conductivity and resulted in the soil consistence transitioning from plastic to liquid behavior following minimal disturbance (Hardie et al, 2012d).…”

“…The soil water characteristic was determined by desorption (Cresswell, 2002), evaporative flux (Wendroth and Wypler, 2008), and inverse solution of tension infiltration data (Šimůnek et al, 1998), reported in Hardie et al (2013b). Saturated hydraulic conductivity was determined by the constant‐head approach on intact cores (McKenzie et al, 2002b) and extrapolation and inverse solution of tension infiltration data (Šimůnek et al, 1998), reported in Hardie et al (2012d, 2013b). Volumetric soil shrinkage was determined by the balloon approach (Cornelis et al, 2006).…”

“…Infiltration processes were investigated by rainfall simulation at rates between 4.1 and 20.6 mm h −1 with 20 to 25 mm of Brilliant Blue dye tracer (4 g L −1 ) when soils were either very dry or at moisture contents near field capacity (Hardie et al, 2011). In situ infiltration and hydraulic conductivity were determined using tension infiltrometers at six supply potentials when the initial soil moisture content was very dry and near field capacity for each of the A1, A2, B21, and B22 horizons (Reynolds and Elrick, 1991; McKenzie et al, 2002a; Hardie et al, 2012d). Soil moisture response to rainfall was monitored during a 21‐mo period using a continuously logging, access‐tube‐mounted capacitance probe, in which the occurrence of preferential flow was indicated by nonsequential soil moisture response with depth (bypass flow) or wetting front velocities 10 times greater than the measured saturated hydraulic conductivity (Hardie et al, 2013a).…”