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Berlin Brandenburg

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  • 11
    Language: English
    In: Soil Science Society of America journal, 2010, Vol.74(4), pp.1084-1091
    Description: Solute diffusion controls important processes in soils: plant uptake of nutrients, sorption–desorption processes, degradation of organic matter, and leaching of radionuclides through clay barriers. We developed a new method for measuring the solute diffusivity (solute diffusion coefficient in the soil relative to water) in intact soil samples (the Multiple Tracer, Filter Separated half-cell method using a Dynamic Model for parameter estimation [MT-FS-DM]). The MT-FS-DM method consists of half-cell diffusion of two pairs of counterdiffusing anionic tracers and a parameter estimation scheme that allows diffusion coefficients for tracers in the two half-cells to be estimated on the basis of two concentration profiles in each sample. The parameter estimation scheme uses a fully dynamic (time-resolved) simulation model. From sensitivity and uncertainty analyses of the dynamic model, we found that the MT-FS-DM method provided reliable results. We compared diffusivities measured on a sandy loam soil using the MT-FS-DM method with diffusivities from six sandy loam test soils from the literature. The new method can be used to estimate solute diffusivity in intact structured soil and provides a more confident estimate for solute diffusion due to the use of two tracer profiles in the same soil sample. Especially when we are interested in determining the diffusivity of a single intact soil sample, such as when relating solute diffusivity to other properties of the soil (e.g., microbial activity), this method will be an improvement over existing methods. ; Includes references ; p. 1084-1091.
    Keywords: Soil Transport Processes ; Labeling Techniques ; Diffusion ; Soil Water Content ; Soil Solution ; Solutes ; Accuracy ; Methodology ; Sandy Loam Soils ; Measurement ; Diffusivity
    ISSN: 0361-5995
    E-ISSN: 14350661
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  • 12
    Language: English
    In: Agriculture, Ecosystems and Environment, 15 September 2012, Vol.159, pp.9-18
    Description: ► Microbial activity decreased significantly at copper concentration ∼500 mg kg . ► Soil compression resistance had an increasing trend with copper concentration. ► Copper contaminated soils had higher amounts of water dispersible clay. ► Clay dispersibility correlated with microbial activity in a copper contaminated field. Copper (Cu) is accumulating in agricultural soils because it is an essential component of mineral fertilizers and pesticides. This could lead to toxic effects on soil macro- and micro-organisms and impact soil structure development. We investigated the effect of historical Cu contamination (〉80 years; from background concentrations up to 3837 mg Cu kg ) on soil microbial enzyme activity, physical properties and resilience to compression. Soil samples and cores were taken from a fallow sandy loam field in Denmark. Microbial activity was quantified using fluorescein diacetate (FDA) and dehydrogenase (DHA) assays. Water dispersible clay was measured on field moist and air dried samples. For the resilience assay, soil cores (drained to −100 hPa) were subjected to uniaxial confined compression (200 kPa) followed by wet–dry or freeze–thaw cycles. Microbial enzyme activity significantly decreased with Cu concentration ≳500 mg kg with the two microbial assays linearly correlated with each other as well as with the water dispersible clay. An effect concentration causing a 50% reduction (EC ) in enzyme activity was observed at 521 mg kg for FDA and 542 mg kg for DHA. Significant increases in water dispersible clay, bulk density and decreases in air-filled porosity and air permeability were observed from Cu ≳ 900 mg kg . The increased density of the contaminated soils led to greater compression resistance and resilience relative to the uncontaminated soil. The results suggest that a threshold level for Cu exists (∼500 mg kg for this soil type) beyond which microbial activity decreases and soil structure becomes more compact with reduced permeability to air.
    Keywords: Soil Contamination ; Dehydrogenase Activity ; Clay Dispersibility ; Air Permeability ; Compression ; Resilience ; Agriculture ; Environmental Sciences
    ISSN: 0167-8809
    E-ISSN: 1873-2305
    Source: ScienceDirect Journals (Elsevier)
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  • 13
    Language: English
    In: Agriculture, ecosystems & environment, 2012, Vol.159, pp.9-18
    Description: Copper (Cu) is accumulating in agricultural soils because it is an essential component of mineral fertilizers and pesticides. This could lead to toxic effects on soil macro- and micro-organisms and impact soil structure development. We investigated the effect of historical Cu contamination (〉80years; from background concentrations up to 3837mg Cukg⁻¹) on soil microbial enzyme activity, physical properties and resilience to compression. Soil samples and cores were taken from a fallow sandy loam field in Denmark. Microbial activity was quantified using fluorescein diacetate (FDA) and dehydrogenase (DHA) assays. Water dispersible clay was measured on field moist and air dried samples. For the resilience assay, soil cores (drained to −100hPa) were subjected to uniaxial confined compression (200kPa) followed by wet–dry or freeze–thaw cycles. Microbial enzyme activity significantly decreased with Cu concentration ≳500mgkg⁻¹ with the two microbial assays linearly correlated with each other as well as with the water dispersible clay. An effect concentration causing a 50% reduction (EC₅₀) in enzyme activity was observed at 521mgkg⁻¹ for FDA and 542mgkg⁻¹ for DHA. Significant increases in water dispersible clay, bulk density and decreases in air-filled porosity and air permeability were observed from Cu≳900mgkg⁻¹. The increased density of the contaminated soils led to greater compression resistance and resilience relative to the uncontaminated soil. The results suggest that a threshold level for Cu exists (∼500mgkg⁻¹ for this soil type) beyond which microbial activity decreases and soil structure becomes more compact with reduced permeability to air. ; p. 9-18.
    Keywords: Wet-Dry Cycles ; Clay ; Bulk Density ; Air Drying ; Agricultural Soils ; Soil Density ; Porosity ; Soil Sampling ; Fluorescein ; Mineral Fertilizers ; Soil Structure ; Soil Toxicity ; Soil Enzymes ; Food And Drug Administration ; Enzyme Activity ; Air ; Pesticides ; Microbial Activity ; Permeability
    ISSN: 0167-8809
    Source: AGRIS (Food and Agriculture Organization of the United Nations)
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  • 14
    Language: English
    In: Soil Science Society of America Journal, Nov-Dec, 2013, Vol.77(6), p.1965(12)
    Description: Soil structure maintains prime importance in determining the ability of soils to carry out essential ecosystem functions and services. This study quantified the newly formed structure of 22-mo field-incubated physically disturbed (2-mm sieved) samples of varying clay mineralogy (illite, kaolinite, and smectite) amended with organic material (7.5 Mg ha-1). The newly formed structure was compared with that of sieved, repacked (SR) and natural intact samples described in previous studies. Assessment and comparison of structural complexity and organization was done using water retention (pore size distribution), soil gas diffusivity, air permeability, and derived pore network complexity parameters. Significant decreases in bulk density and increases in pores 〉100 ?m were observed for incubated samples compared with SR samples. For the soils studied, the proportion of pores 〉100 ?m increased in the order: smectite 〈 illite 〈 kaolinite, with no effect of organic amendment. Soil structural complexity, quantified by soil gas diffusivity, air permeability, and derived pore network indices, was greater for incubated than SR samples. For illitic soils, incubated samples had lower water content and higher air-filled porosity and air permeability than natural intact samples at a matric potential of -10 kPa. Despite this, soil pore organization was similar for both natural and incubated soils, but pore network complexity increased in the order: SR 〈 incubated 〈 natural soils. Finally, the air permeability percolation threshold corresponding to the physically based diffusion threshold increased with structural complexity (SR = 0.02 ?m2; incubated = 0.20 ?m2; natural = 0.70 ?m2). Thus, critical reexamination is needed of the often-used 1.0-?m2 percolation threshold for convective air transport when analyzing pore network complexity. Lack of a clear effect of organic amendment for incubated samples suggests using higher application rates in future studies.
    Keywords: Porosity -- Analysis ; Soil Permeability -- Analysis ; Soil Research
    ISSN: 0361-5995
    E-ISSN: 14350661
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  • 15
    Language: English
    In: Soil Science Society of America journal, 2012, Vol.76(1), pp.18-27
    Description: Accurate estimation of soil gas diffusivity (Dp/Do, the ratio of gas diffusion coefficients in soil and free air) and air permeability (ka) from basic texture and pore characteristics will be highly valuable for modeling soil gas transport and emission and their field-scale variations. From the topsoil of two Danish arable fields representing two natural clay gradients, Dp/Do and ka were measured at soil water matric potentials between −1 and −100 kPa on undisturbed soil cores. The Rosin–Rammler particle size distribution parameters α and β (characteristic particle size and degree of sorting, respectively) and the Campbell water retention parameter b were used to characterize particle and pore size distributions, respectively. Campbell b yielded a wide interval (4.6–26.2) and was highly correlated with α, β, and volumetric clay content. Both Dp/Do and ka followed simple power-law functions (PLFs) of air-filled porosity (εa). The PLF tortuosity–connectivity factors (X*) for Dp/Do and ka were both highly correlated with all basic soil characteristics, in the order of volumetric clay content = Campbell b 〉 gravimetric clay content 〉 α 〉 β. The PLF water blockage factors (H) for Dp/Do and ka were also well (but relatively more weakly) correlated with the basic soil characteristics, again with the best correlations to volumetric clay content and b. As a first attempt at developing a simple Dp/Do model useful at the field scale, we extended the classical Buckingham Dp/Do model (εa2) by a scaling factor based on volumetric clay content. The scaled Buckingham model provided accurate predictions of Dp(εa)/Do across both natural clay gradients. ; p. 18-27.
    Keywords: Clay ; Particle Size ; Topsoil ; Texture ; Prediction ; Porosity ; Models ; Soil Water ; Soil Air ; Sorting ; Air ; Particle Size Distribution ; Permeability ; Diffusivity
    ISSN: 0361-5995
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  • 16
    Language: English
    In: Soil Science Society of America Journal, March-April, 2014, Vol.78(2), p.377(10)
    Description: Quantitative characterization of aggregate pore structure can reveal the evolution of aggregates under different land use and management practices and their effects on soil processes and functions. Advances in X-ray computed tomography (CT) provide powerful means to conduct such characterization. This study examined aggregate pore structure of three differently managed same textured Danish soils (mixed forage cropping, MFC; mixed cash cropping, MCC; cereal cash cropping, CCC) for (i) natural aggregates, and (ii) aggregates regenerated after 20 mo of incubation. In total, 27 aggregates (8-16 mm) were sampled from nine different treatments; three natural soils and three repacked lysimeters without and three with organic matter (OM; ground rape) amendment. Three dimensional X-ray CT images, tensile strength, and organic carbon (OC) were obtained for each aggregate. Aggregate-associated OC differed significantly between the three soils as 2.1, 1.4, and 1.0% for MFC, MCC, and CCC, respectively. Aggregate porosity and pore connectivity were significantly higher for CCC aggregates than for MFC and MCC aggregates. The CCC aggregates had an average pore diameter of 300 ?m, whereas MFC and MCC had an average pore diameter of 200 and 170 ?m, respectively. Pore shape analysis indicated that CCC and MFC aggregates had an abundance of rounded and elongated pores, respectively, and those of MCC were in-between CCC and MFC. Aggregate pore structure development in the lysimeters was nearly similar irrespective of the soil type and organic matter amendment, and was vastly different from the state of natural aggregates. Aggregate porosity (〉30 ?m) was observed to be a good predictor for the mechanical properties of aggregates. In general natural aggregates were stronger than lysimeter aggregates.
    Keywords: Cat Scans -- Usage ; Porosity -- Research ; Soil Research
    ISSN: 0361-5995
    E-ISSN: 14350661
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  • 17
    Language: English
    In: Soil Science Society of America Journal, March-April, 2014, Vol.78(2), p.422(12)
    Description: Changes in soil water content are known to affect soil reflectance. Even though it was suggested some time ago that the phenomenon of increased forward scattering due to the presence of water in the soil is related to water film thickness and matric potential, there has been no detailed investigation of this in any studies. The effects of moisture conditions on visible near-infrared (vis-NIR) spectra of four representative soils in Denmark have been assessed as a function of both water film thickness (expressed as the number of molecular layers) and matric potential. Complete water retention curves, from wet (pF 0.3, pF = log(|j|), where ? is the matric potential in cm) to hyper dry end (oven-dried and freeze-dried soil), were obtained by initial wetting followed by successive draining and drying of soil samples, performing NIR measurements at each step. Soil reflectance was found to decrease systematically, yet not proportionally, with decreasing matric potential and increasing molecular layers. The changes in molecular layers were best captured by the soil reflectance of clay-rich soils. Here the largest increase in reflectance occurred between pF 3 and 4, caused by the shift from capillary to adsorptive surface forces. In support of this, the smallest changes in reflectance were seen in the sandiest soil. Freeze drying the soil highest in organic C increased reflectance, possibly due to an alteration in organic matter during freezing. The different reflectance behavior of soil with a higher organic C content may be linked to differences in the amount, but also the quality (higher hydrophobicity) of the organic matter. However, this needs to be confirmed in further studies.
    Keywords: Reflectance -- Research ; Molecules -- Research ; Soil Research
    ISSN: 0361-5995
    E-ISSN: 14350661
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  • 18
    Language: English
    In: Soil Science Society of America journal, 2011, Vol.75(4), pp.1315-1329
    Description: Accurate predictions of the soil-gas diffusivity (Dp/Do, where Dp is the soil-gas diffusion coefficient and Do is the diffusion coefficient in free air) from easily measureable parameters like air-filled porosity (ε) and soil total porosity (ϕ) are valuable when predicting soil aeration and the emission of greenhouse gases and gaseous-phase contaminants from soils. Soil type (texture) and soil density (compaction) are two key factors controlling gas diffusivity in soils. We extended a recently presented density-corrected Dp(ε)/Do model by letting both model parameters (α and β) be interdependent and also functions of ϕ. The extension was based on literature measurements on Dutch and Danish soils ranging from sand to peat. The parameter α showed a promising linear relation to total porosity, while β also varied with α following a weak linear relation. The thus generalized density-corrected (GDC) model gave improved predictions of diffusivity across a wide range of soil types and density levels when tested against two independent data sets (total of 280 undisturbed soils or soil layers) representing Danish soil profile data (0–8 m below the ground surface) and performed better than existing models. The GDC model was further extended to describe two-region (bimodal) soils and could describe and predict Dp/Do well for both different soil aggregate size fractions and variably compacted volcanic ash soils. A possible use of the new GDC model is engineering applications such as the design of highly compacted landfill site caps. ; p. 1315-1329.
    Keywords: Data Collection ; Sand ; Soil Profiles ; Texture ; Landfills ; Prediction ; Engineering ; Soil Density ; Porosity ; Models ; Peat ; Greenhouse Gas Emissions ; Aeration ; Air ; Volcanic Ash Soils ; Diffusivity
    ISSN: 0361-5995
    E-ISSN: 14350661
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  • 19
    Language: English
    In: Soil Science Society of America journal, 2011, Vol.75(3), pp.795-806
    Description: The air permeability (ka) and soil gas diffusion coefficients (Dp) are controlling factors for gas transport and fate in variably saturated soils. We developed a unified model for ka and Dp based on the classical Archie's law, extended by: (i) allowing for two-region gas transport behavior for structured soils, with the natural field moisture condition (set at −100 cm H2O matric potential [pF 2]) as the reference (spliced) point between the large-pore (drained pore diameter ≥30 μm at pF ≤ 2) and the small-pore (subsequently drained pores 2) regions, and (ii) including a percolation threshold, set as 10% of the total porosity for structureless porous media or 10% of the porosity in the large-pore region for structured soils. The resulting extended Archie's law with reference point (EXAR) models for ka and Dp were fitted to the measured data. For both structureless and structured porous media, Archie's saturation exponent (n) was higher for Dp than for ka, indicating higher water blockage effects on gas diffusion. For structured soils, the saturation exponent for the large-pore region (n1) was lower than for the small-pore region (n2). Generally, n1 values of∼1 for ka and 2 for Dp and n2 values of 4/3 for ka and 7/3 for Dp described the data well. Two reference-point expressions for ka at pF 2 were also developed and tested together with existing models for Dp at pF 2 against independent data across soil types. The best-performing reference-point models were a ka model based on the classical Kozeny equation and the Moldrup Dp model. ; p. 795-806.
    Keywords: Models ; Water ; Soil Air ; Soil Types ; Porous Media ; Air ; Equations ; Permeability ; Porosity ; Diffusivity
    ISSN: 0361-5995
    E-ISSN: 14350661
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  • 20
    Language: English
    In: Soil Science Society of America Journal, Sept-Oct, 2013, Vol.77(5), p.1517(12)
    Description: Time domain reflectometry (TDR) is used widely for measuring soil-water content. New TDR coil probe technology facilitates the development of small, nondestructive probes for simultaneous measurement of soil-water content (?) and soil-water potential (?). In this study we developed mini tensiometer-time domain reflectometry (T-TDR) coil probes, 6-mm wide and 32-mm long. The coil probes were calibrated against a conventional three-rod probe and were used for measuring ? for a aggregated volcanic ash soil (VAS) and a uniform sand. A commonly-used dielectric mixing model did not accurately describe the measured relation between the dielectric constant of the T-TDR coil probe (?coil) and ?, and a new calibration model for ?coil (?) was proposed instead. The new model assumes single-region behavior for sand and two-region behavior for aggregated VAS, when plotting the normalized dielectric constant of the coil probe (?coil-? dry; where ?dry is the dielectric constant of the T-TDR coil probe for air-dried material) as a function of ?. The new calibration model accurately described the (?coil-? dry)-? relations measured by 7 T-TDR coil probes on both sand and VAS. Additionally, there was a good agreement between measured soil-water retention curves (? 〉 -100 cm H2O) by the new T-TDR coil probes and independent measurements by the hanging water column method.
    Keywords: Reflectometers -- Usage ; Soil Research
    ISSN: 0361-5995
    E-ISSN: 14350661
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