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Berlin Brandenburg

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  • 1
    Language: English
    In: Vadose Zone Journal, 2012, Vol.11(3), p.0
    Description: Recently, a new approach was introduced to directly measure unsaturated hydraulic conductivity in flux-controlled experiments--the multistep flux experiment. Thereby an overshoot in matric potential h (sub m) across drainage and infiltration fronts was observed. We extended this experimental approach to simultaneously measure the volumetric water content Theta within the sample and applied the method to a sand and a clay loam soil. The detailed trajectories within the h (sub m) -Theta space were obtained during a number of decreasing and increasing steps in infiltration rate. This clearly demonstrates the type and magnitude of hydraulic nonequilibrium under transient conditions where water content and matric potential deviate from a well-defined static relation. We also compared the directly measured hydraulic conductivities with those obtained from classical multistep outflow experiments and found that nonequilibrium dynamics might lead to an underestimation of hydraulic conductivity when obtained from an inverse solution of Richards" equation. We provide a qualitative explanation of nonequilibrium that depends on the structure of the material and the type and magnitude of external forcing. The new experimental setup is considered to be a valuable tool to actually quantify nonequilibrium effects. This will make it possible to represent this relevant phenomenon in future modeling concepts.
    Keywords: Hydrogeology ; Aquifers ; Climate Forcing ; Discharge ; Drainage ; Experimental Studies ; Ground Water ; Hydraulic Conductivity ; Hydrodynamics ; Hysteresis ; Infiltration ; Models ; Richards Equation ; Saturation ; Soil Mechanics ; Solute Transport ; Transport ; Unsaturated Zone;
    ISSN: Vadose Zone Journal
    E-ISSN: 1539-1663
    Source: CrossRef
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  • 2
    Language: English
    In: Vadose Zone Journal, 2011, Vol.10(3), p.988
    Description: Recent studies have shown that rhizosphere hydraulic properties may differ from those of the bulk soil. Specifically, mucilage at the root-soil interface may increase the rhizosphere water holding capacity and hydraulic conductivity during drying. The goal of this study was to point out the implications of such altered rhizosphere hydraulic properties for soil-plant water relations. We addressed this problem through modeling based on a steady-rate approach. We calculated the water flow toward a single root assuming that the rhizosphere and bulk soil were two concentric cylinders having different hydraulic properties. Based on our previous experimental results, we assumed that the rhizosphere had higher water holding capacity and unsaturated conductivity than the bulk soil. The results showed that the water potential gradients in the rhizosphere were much smaller than in the bulk soil. The consequence is that the rhizosphere attenuated and delayed the drop in water potential in the vicinity of the root surface when the soil dried. This led to increased water availability to plants, as well as to higher effective conductivity under unsaturated conditions. The reasons were two: (i) thanks to the high unsaturated conductivity of the rhizosphere, the radius of water uptake was extended from the root to the rhizosphere surface; and (ii) thanks to the high soil water capacity of the rhizosphere, the water depletion in the bulk soil was compensated by water depletion in the rhizosphere. We conclude that under the assumed conditions, the rhizosphere works as an optimal hydraulic conductor and as a reservoir of water that can be taken up when water in the bulk soil becomes limiting.
    Keywords: Agriculture;
    ISSN: Vadose Zone Journal
    E-ISSN: 1539-1663
    Source: CrossRef
    Library Location Call Number Volume/Issue/Year Availability
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