Kooperativer Bibliotheksverbund

Berlin Brandenburg

and
and

Your email was sent successfully. Check your inbox.

An error occurred while sending the email. Please try again.

Proceed reservation?

Export
Filter
  • Agriculture
Type of Medium
Language
Year
  • 1
    Language: English
    In: Vadose Zone Journal, 2015, Vol.14(5), p.0
    Description: The guest editors introduce the seven contributions to the special issue on processes in capillary fringes, with a focus on the complex interaction of biological, chemical, and physical processes in this environemnt. Processes in capillary fringes (CFs) have a complex nature due to the interactions between the solid, liquid, and gaseous environments. Despite a considerable body of literature on CFs coming from different disciplines, the ongoing processes and their complex interactions are yet only partially understood.
    Keywords: Soils ; Solids ; Vadose Water ; Methods and Instruments ; General;
    ISSN: Vadose Zone Journal
    E-ISSN: 1539-1663
    Source: CrossRef
    Library Location Call Number Volume/Issue/Year Availability
    BibTip Others were also interested in ...
  • 2
    Language: English
    In: Plant and Soil, 2010, Vol.332(1), pp.163-176
    Description: Water flow from soil to plants depends on the properties of the soil next to roots, the rhizosphere. Although several studies showed that the rhizosphere has different properties than the bulk soil, effects of the rhizosphere on root water uptake are commonly neglected. To investigate the rhizosphere’s properties we used neutron radiography to image water content distributions in soil samples planted with lupins during drying and subsequent rewetting. During drying, the water content in the rhizosphere was 0.05 larger than in the bulk soil. Immediately after rewetting, the picture reversed and the rhizosphere remained markedly dry. During the following days the water content of the rhizosphere increased and after 60 h it exceeded that of the bulk soil. The rhizosphere’s thickness was approximately 1.5 mm. Based on the observed dynamics, we derived the distinct, hysteretic and time-dependent water retention curve of the rhizosphere. Our hypothesis is that the rhizosphere’s water retention curve was determined by mucilage exuded by roots. The rhizosphere properties reduce water depletion around roots and weaken the drop of water potential towards roots, therefore favoring water uptake under dry conditions, as demonstrated by means of analytical calculation of water flow to a single root.
    Keywords: Root water uptake ; Water retention curve ; Rhizosphere ; Neutron radiography ; Mucilage ; Hysteresis
    ISSN: 0032-079X
    E-ISSN: 1573-5036
    Library Location Call Number Volume/Issue/Year Availability
    BibTip Others were also interested in ...
  • 3
    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
    Library Location Call Number Volume/Issue/Year Availability
    BibTip Others were also interested in ...
  • 4
    Language: English
    In: Vadose Zone Journal, 2015, Vol.14(5), p.0
    Description: We used X-ray computed microtomography to study gas trapping in a fluctuating water table. Our results show that capillary forces control trapping and phase distribution in dynamic capillary fringes. In porous media, the nonwetting phase is trapped on water saturation due to capillary forces acting in a heterogeneous porous structure. Within the capillary fringe, the gas phase is trapped and released along with the fluctuation of the water table, creating a highly active zone for biological transformations and mass transport. We conducted column experiments to observe and quantify the magnitude and structure of the trapped gas phase at the pore scale using computed microtomography. Different grain size distributions of glass beads were used to study the effect of the pore structure on trapping at various capillary numbers. Viscous forces were found to have negligible impact on phase trapping compared with capillary and buoyancy forces. Residual gas saturations ranged from 0.5 to 10%, while residual saturation increased with decreasing grain size. The gas phase was trapped by snap-off in single pores but also in pore clusters, while this single-pore trapping was dominant for grains larger than 1 mm in diameter. Gas surface area was found to increase linearly with increasing gas volume and with decreasing grain size.
    Keywords: Grain Size ; Water Table ; Mass Transport ; Buoyancy ; Pores ; Porous Media ; Particle Size ; Water Table ; Saturation ; Vadose Water ; Fluctuations ; Trapping ; Buoyancy ; Methods and Instruments ; General;
    ISSN: Vadose Zone Journal
    E-ISSN: 1539-1663
    Source: CrossRef
    Library Location Call Number Volume/Issue/Year Availability
    BibTip Others were also interested in ...
  • 5
    Language: English
    In: Geoderma, 01 June 2018, Vol.319, pp.132-141
    Description: Irrigation with treated waste water (TWW) is a common practice in agriculture, mainly in arid and semiarid areas as it provides a sustainable water resource available at all-season in general and at freshwater shortage in particular. However, TWW still contains abundant organic material which is known to decrease soil wettability, which in turn may promote flow instabilities that lead to the formation of preferential flow paths. We investigate the impact of long-term TWW irrigation on water wettability and infiltration into undisturbed soil cores from two commercially used orchards in Israel. Changes of water content during infiltration were quantitatively analysed by X-ray radiography. One orchard (sandy clay loam) had been irrigated with TWW for more than thirty years. In the other orchard (loamy sand) irrigation had been changed from freshwater to TWW in 2008 and switched back in some experimental plots to freshwater in 2012. Undisturbed soil cores were taken at the end of the dry and the rainy season to investigate the seasonal effect on water repellency and on infiltration dynamics in the laboratory. The irrigation experiments were done on field moist samples. A test series with different initial water contents was run to detect the influence on water movement at different wettabilities. In this study we show that the infiltration front stability is dependent on the history of waste water irrigation at the respective site and on the initial water content.
    Keywords: Soil Water Repellency ; Treated Waste Water Irrigation ; Unstable Flow ; Preferential Flow ; Water Infiltration ; X-Ray Analysis ; Agriculture
    ISSN: 0016-7061
    E-ISSN: 1872-6259
    Library Location Call Number Volume/Issue/Year Availability
    BibTip Others were also interested in ...
  • 6
    Language: English
    In: Vadose Zone Journal, 01 March 2018, Vol.17(1)
    Description: X-ray radiography is a suitable approach to study water dynamics in undisturbed soil. However, beam hardening impairs the deduction of soil moisture changes from X-ray attenuation, especially when studying infiltration of water into cylindrical soil columns. We developed a calibration protocol to correct for beam hardening effects that enables the quantitative determination of changing average water content in two-dimensional projections. The method works for a broad range of materials and is easy to implement. Moreover, we studied the drift of X-ray attenuation values due to the detector latency and eliminated its contribution to the quantitative analysis. Finally we could visualize the dynamics of infiltrating water into undisturbed cylindrical soil samples.
    Keywords: Agriculture
    ISSN: 1539-1663
    E-ISSN: 1539-1663
    Source: Directory of Open Access Journals (DOAJ)
    Library Location Call Number Volume/Issue/Year Availability
    BibTip Others were also interested in ...
  • 7
    Language: English
    In: Vadose Zone Journal, 2011, Vol.10(2), p.654
    Description: The unsaturated hydraulic conductivity function is the dominant material property for modeling soil water dynamics. Because it is difficult to measure directly, it is often derived from the water retention characteristic combined with a geometric model of the pore space. In this study, we developed an automated, simple multistep flux (MSF) experiment to directly measure unsaturated conductivities, K(psi (sub m) ), at a number of water potentials, psi (sub m) , using the experimental setup of classical multistep outflow (MSO) experiments. In contrast to the MSO experiment, the MSF experiment measures the conductivity directly at a spatially constant water potential assuming macroscopically homogeneous materials. Additionally, the proposed method reveals the hysteresis of K(psi (sub m) ) with respect to increasing and decreasing water potentials as well as the temporal dynamics of K(psi (sub m) ) during transient-flow conditions. This temporal behavior is explained by the dynamics of fluid configurations at the pore scale during drainage and imbibition leading to hydraulic nonequilibrium. It may provoke a systematic underestimation of hydraulic conductivity using inverse optimization of K(psi (sub m) ) based on classical MSO experiments. The new approach will improve the determination of K(psi (sub m) ) and it provides an experimental tool to quantify the effects of hydraulic nonequilibrium under transient conditions.
    Keywords: Hydrogeology ; Experimental Studies ; Geometry ; Ground Water ; Hydraulic Conductivity ; Hysteresis ; Inverse Problem ; Mathematical Methods ; Measurement ; Models ; Movement ; Optimization ; Phase Equilibria ; Soils ; Unsaturated Zone;
    ISSN: Vadose Zone Journal
    E-ISSN: 1539-1663
    Source: CrossRef
    Library Location Call Number Volume/Issue/Year Availability
    BibTip Others were also interested in ...
  • 8
    Language: English
    In: Vadose Zone Journal, 2011, Vol.10(3), p.1082
    Description: Predicting solute transport through structured soil based on observable structural properties of the material has not been accomplished to date. We evaluated a new approach to predicting breakthrough curves (BTCs) of dissolved chemicals in intact structured soil columns based on attributes of the pore structure at hierarchical spatial scales. The methodology centers on x-ray computed microtomography of a hierarchic suite of undisturbed soil samples (diameters 1, 4.6, 7.5, and 16 cm) to identify the network of pores 〉10 mu m in diameter. The pore structure was quantified in terms of pore size distribution, interface area density, and connectivity. The pore size distribution and pore connectivity were used to set up an equivalent pore network model (PNM) for predicting the BTCs of Br (super -) and Brilliant Blue FCF (BB) at unsaturated, steady-state flux. For a structured silt loam soil column, the predictions of Br (super -) tracer breakthrough were within the variation observed in the column experiments. A similarly good prediction was obtained for Br (super -) breakthrough in a sandy soil column. The BB breakthrough observed in the silt loam was dominated by a large variation in sorption (retardation factors between R = 2.9 and 24.2). The BB sorption distribution coefficient, k (sub d) , was measured in batch tests. Using the average k (sub d) in the PNM resulted in an overestimated retardation (R = 28). By contrast, breakthrough of BB in the sandy soil (experimental R = 3.3) could be roughly predicted using the batch test k (sub d) (PNM simulation R = 5.3). The prediction improved when applying a sorption correction function accounting for the deviation between measured interface area density distribution and its realization in the network model (R = 4.1). Overall, the results support the hypothesis that solute transport can be estimated based on a limited number of characteristics describing pore structure: the pore size distribution, pore topology, and pore-solid interfacial density.
    Keywords: Soils ; Bad Lauchstadt Germany ; Boundary Conditions ; Breakthrough Curves ; Bromine ; Central Europe ; Central Germany ; Chemical Dispersion ; Chernozems ; Computed Tomography ; Convection ; Density ; Dye Tracers ; Equations ; Europe ; Experimental Studies ; Fuhrberg Germany ; Germany ; Halogens ; Image Analysis ; Laboratory Studies ; Lower Saxony Germany ; Microtomography ; Minckowski Functions ; Morphology ; Networks ; Podzols ; Porosity ; Quantitative Analysis ; Saxony-Anhalt Germany ; Simulation ; Soils ; Solute Transport ; Spectra ; Tomography ; Topology ; Transport ; X-Ray Spectra;
    ISSN: Vadose Zone Journal
    E-ISSN: 1539-1663
    Source: CrossRef
    Library Location Call Number Volume/Issue/Year Availability
    BibTip Others were also interested in ...
  • 9
    Language: English
    In: Vadose Zone Journal, 2013, Vol.12(4), p.0
    Description: The hydraulic behavior of soil is determined by its hydraulic properties and their variability in space. In agricultural soils, this heterogeneity may stem from tillage or may have natural origin. The root distribution of plants will adapt to some extent to this soil heterogeneity. However, the combined impact of soil heterogeneity and root water uptake (RWU) on long-term soil water budgets has not received much attention. Numerical experiments helped identify how soil heterogeneity affects plant transpiration, soil evaporation, and groundwater recharge. Two-dimensional virtual soils with hierarchical heterogeneity, both natural and tillage induced, served as a basis for modeling soil water dynamics for a 10-yr climate record from two weather stations in Germany that vastly differ in annual precipitation. The complex interactions between soil and vegetation were explored by (i) comparing different RWU strategies (depth-, structure-, and time-dependent root profiles), (ii) land use types (perennial grass and annual winter crops), (iii) a combination of textures (silt above sand and sand above loam), and (iv) RWU with or without a compensation mechanism. The simulations were repeated with one-dimensional, effective representations of these virtual soils. In the framework of hydropedology, this study shed some light on the interaction between plants and pedological features and its impact on the macroscopic soil water budget. We demonstrated that land use has a major impact on the annual water balance through the partitioning of evapotranspiration into bare soil evaporation and plant transpiration. Compensational RWU becomes important for the annual water balance when the root zone comprises contrasting materials with respect to water holding capacity. Soil heterogeneity has in fact a minor impact on long-term soil water budgets. As a consequence, the relative contribution of plant transpiration, soil evaporation, and groundwater recharge to the total soil water loss was well reproduced by simulations in one-dimensional effective soil profiles. This advocates the application of one-dimensional soil-atmosphere-vegetation transfer (SVAT) models at larger scales. These findings only hold for assumptions made in our numerical simulations including flat area without lateral flow and no macropore flow.
    Keywords: Environmental Geology ; Soils ; Atmosphere ; Boundary Conditions ; Central Europe ; Eastern Germany ; Europe ; Field Studies ; Germany ; Grain Size ; Heterogeneity ; Hydrodynamics ; Hydrology ; Hydropedology ; Julicher Borde Germany ; Land Use ; Magdeburg Germany ; Mapping ; North Rhine-Westphalia Germany ; Numerical Models ; One-Dimensional Models ; Rhizosphere ; Saxony-Anhalt Germany ; Scale Factor ; Size Distribution ; Soil-Atmosphere-Vegetation Transfer ; Soils ; Topography ; Two-Dimensional Models ; Unsaturated Zone ; Vegetation ; Water Balance ; Western Germany;
    ISSN: Vadose Zone Journal
    E-ISSN: 1539-1663
    Source: CrossRef
    Library Location Call Number Volume/Issue/Year Availability
    BibTip Others were also interested in ...
  • 10
    Language: English
    In: Vadose Zone Journal, 2013, Vol.12(3), p.0
    Description: Soils are structured on multiple spatial scales, originating from inhomogeneities of the parent material, pedogenesis, soil organisms, plant roots, or tillage. This leads to heterogeneities that cause variability of local measurements of hydraulic state variables and affects the flow behavior of water in soil. Whereas in real-world systems, the true underlying structures can never be absolutely known, it is appealing to employ synthetic or "virtual" experiments for assessing general properties of flow in porous media and grasping the main physical mechanisms. With this aim, three two-dimensional virtual realities with increasing structural complexity, representing cultivated soils with hierarchical spatial heterogeneity on multiple scales were constructed by the interdisciplinary research group Virtual Institute of the Helmholtz Association (INVEST). At these systems, numerical simulations of water dynamics including a heavy rain, a redistribution, and a long-lasting evaporation period were performed. The technical aspects of the construction of the virtual soils and results of the forward simulations have been presented in a paper by Schluter et al. (2012). In this follow-up paper, we use inverse modeling to investigate measurements in virtual vertical soil profiles, mimicking typical field monitoring campaigns with moisture content and matric potential sensors placed at five depths. Contrary to the real situation, we can interpret observed data, their variability, estimated hydraulic properties, and predicted water balance in the light of the known truth. Our results showed that measurements, particularly those of water contents, varied strongly with measuring position. Using data from single profiles in systems similar to our virtual soils thus will lead to very different estimates of the soil hydraulic properties. As a consequence, the correct calculation of the water balance is rather a lucky coincidence than the rule. However, the average of the predicted water balances obtained from the one-dimensional simulations, and the estimated soil hydraulic properties agreed very well with those attained from the two-dimensional systems.
    Keywords: Soils ; Hydrogeology ; Boundary Interactions ; Evaporation ; Grain Size ; Heterogeneous Materials ; Hydrodynamics ; Infiltration ; Interpretation ; Inverse Problem ; Irrigation ; Matric Head ; Measurement ; Moisture ; One-Dimensional Models ; Quantitative Analysis ; Simulation ; Size Distribution ; Soils ; Spatial Distribution ; Tdr Data ; Two-Dimensional Models ; Unsaturated Zone ; Van Genuchten-Mualem Parameters ; Water ; Water Balance;
    ISSN: Vadose Zone Journal
    E-ISSN: 1539-1663
    Source: CrossRef
    Library Location Call Number Volume/Issue/Year Availability
    BibTip Others were also interested in ...
Close ⊗
This website uses cookies and the analysis tool Matomo. Further information can be found on the KOBV privacy pages