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  • 11
    Language: English
    In: Vadose Zone Journal, 2012, Vol.11(4), p.0
    Description: The hydraulic behavior of soil is determined by the spatial heterogeneity of its hydraulic properties. The interplay among parent material, pedogenesis, and tillage leads to characteristic structures in cultivated soils. Tillage-induced features like a loosely aggregated seed bed, a compacted plow pan, and soil compaction beneath tractor ruts overlay natural features such as facies and horizons. Assessing the impact of such structural components on vadose zone hydrology requires an observation scale of several meters and a resolution in the range of centimeters, which is not feasible with experimental setups. An alternative solution is the generation of synthetic but realistic structures and their hydraulic properties as a basis for modeling the hydraulic behavior in response to different boundary conditions. With such "virtual soils" at hand, comparative studies are possible that help explore the relation between soil architecture and soil function. We developed a structure generator that provides great flexibility in the design of virtual soils with nested heterogeneity. Virtual soils with increasing complexity were generated to explore scenarios of precipitation and evaporation for a period of several months. The simulations demonstrated that the structure and the hydraulic properties close to the soil surface originating from tillage clearly govern atmospheric boundary fluxes, while the impact of heterogeneity on groundwater recharge is more complex due to threshold effects, hydraulic nonequilibrium, and the interaction with atmospheric forcing. A comparison with one-dimensional, effective representations of these virtual soils demonstrated that upscaling of soil water dynamics becomes inaccurate when lateral fluxes become relevant at the scale of observation.
    Keywords: Hydrogeology ; Soils ; Agriculture ; Air ; Aquifers ; Boundary Conditions ; Ground Water ; Heterogeneity ; Hydraulic Conductivity ; Hydrodynamics ; Moisture ; Morphology ; Recharge ; Simulation ; Soil-Atmosphere Interface ; Soils ; Tillage ; Topsoil ; Unsaturated Zone ; Virtual Reality ; Water;
    ISSN: Vadose Zone Journal
    E-ISSN: 1539-1663
    Source: CrossRef
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  • 12
    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
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  • 13
    Language: English
    In: Vadose Zone Journal, 2009, Vol.8(3), p.805
    Description: It has been speculated that during periods of water deficit, roots may shrink and lose contact with the soil, with a consequent reduction in root water uptake. Due to the opaque nature of soil, however, this process has never been observed in situ for living plants. Through x-ray tomography and image analysis, we have demonstrated the formation and dynamics of air gaps around roots. The high spatial resolution required to image the soil–root gaps was achieved by combining tomography of the entire sample (field of view of 16 by 16 cm, pixel side 0.32 mm) with local tomography of the soil region around the roots (field of view of 5 by 5 cm, pixel side 0.09 mm). For a sandy soil, we found that when the soil dries to a water content of 0.025 m3 m–3, gaps occur around the taproot and the lateral roots of lupin (Lupinus albus L.). Gaps were larger for the taproot than the laterals and were caused primarily by root shrinkage rather than by soil shrinkage. When the soil was irrigated again, the roots swelled, partially refilling the gaps; however, large gaps persisted in the more proximal, older part of the taproot. Gaps are expected to reduce water transfers between soil and roots. Opening and closing of gaps may help plants to prevent water loss when the soil dries, and to restore the soil–root continuity when water becomes available. The persistence of gaps in the more proximal parts is one reason why roots preferentially take up water from their more distal parts. ; Includes references ; p. 805-809.
    Keywords: Soil Water Content ; Roots ; Soil-Plant Interactions ; Shrinkage ; Plants ; Translocation (Plant Physiology) ; Lupinus Albus ; Forage Legumes ; Spatial Variation ; Drought ; Water Stress ; Sandy Soils ; Water Uptake ; Computed Tomography ; Forage Crops ; Image Analysis ; Taproots;
    ISSN: Vadose Zone Journal
    E-ISSN: 1539-1663
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  • 14
    Article
    Article
    Language: English
    In: Vadose Zone Journal, 01 July 2019, Vol.18(1)
    Description: Soil hydrology is a key control for the functioning of the terrestrial environment. Many environmental issues that we need to tackle today are directly linked to soil water dynamics. This includes agricultural production and food security, nutrient cycling and carbon storage, prevention of...
    Keywords: Agriculture
    ISSN: 1539-1663
    E-ISSN: 1539-1663
    Source: Directory of Open Access Journals (DOAJ)
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  • 15
    Language: English
    In: Vadose Zone Journal, 01 June 2019, Vol.18(1)
    Description: Biological activity in soil causes fluxes of O into and CO out of the soil with significant global relevance. Hence, the dynamics of CO concentrations in soil can be used as an indicator for biological activity. However, there is an enormous spatial and temporal variability in soil respiration,...
    Keywords: Agriculture
    ISSN: 1539-1663
    E-ISSN: 1539-1663
    Source: Directory of Open Access Journals (DOAJ)
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