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Berlin Brandenburg

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  • AGRIS (United Nations, Food and Agriculture Organization)  (48)
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  • 1
    In: Soil Science Society of America Journal, January 2012, Vol.76(1), pp.51-60
    Description: Solute diffusivity in soil plays a major role in many important processes with relation to plant growth and environmental issues. Soil solute diffusivity is affected by the volumetric water content as well as the morphological characteristics of water‐filled pores. The solute diffusivity in intact soil samples from two different tillage treatments (soil from below the depth of a harrow treatment and soil from within a moldboard plowed plow layer) was estimated based on concentration profiles using a newly developed method. The method makes use of multiple tracers (two sets of counterdiffusing tracers) for a better determination of the diffusivity. The diffusivity was higher in the below‐till soil than the plowed soil at the same soil water matric potential due to higher water content but also due to higher continuity and lower tortuosity of the soil pores. We measured identical solute diffusivities independent of the tracer set used. We analyzed the whole data set using Archie's law and found a linear relation between Archie's exponent and the logarithm of the soil water matric suction in centimeters of water (pF). An analysis of seven data sets from the literature showed that this was a general trend for soils with moderate to low clay contents.
    Keywords: Clay ; Data Collection ; Soil Water Content ; Soil Pore System ; Soil Treatment ; Solutes ; Soil Sampling ; Soil Water ; Plowing ; Tracer Techniques ; Plant Growth ; Water Content ; Harrows ; Diffusivity;
    ISSN: 0361-5995
    E-ISSN: 1435-0661
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  • 2
    Language: English
    In: Soil Science Society of America journal, 2012, Vol.76(5), pp.1509-1517
    Description: The gas diffusion coefficient (Ds,g) and solute diffusion coefficient (D(s,l)) and their dependencies on fluid content (κ) (equal to soil–air content θ for D(s,g) and soil–water content ɛ for D(s,l)) are controlling factors for gas and solute transport in variably saturated soils. In this study, we propose unified, predictive models for D(s,g)(ɛ) and D(s,l)(θ) based on modifying and extending the classical Maxwell model at fluid saturation with a fluid-induced reduction term including a percolation threshold (ɛ(th) for D(s,g) and θ(th) for D(s,l)). Different percolation threshold terms adopted from recent studies for gas (D(s,g)) and solute (D(s,l)) diffusion were applied. For gas diffusion, ɛth was a function of bulk density (total porosity), while for solute diffusion θ(th) was best described by volumetric content of finer soil particles (clay and organic matter), FINES(vol). The resulting LIquid and GAs diffusivity and tortuosity (LIGA) models were tested against D(s,g) and D(s,l) data for differently-textured soils and performed well against the measured data across soil types. A sensitivity analysis using the new Maxwell’s Law based LIGA models implied that the liquid phase but not the gaseous-phase tortuosity was controlled by soil type. The analyses also suggested very different pathways and fluid-phase connectivity for gas and solute diffusion in unsaturated soil. In conclusion, the commonly applied strategy of using the same, soil-type-independent model for gas and solute diffusivity in analytical and numerical models for chemical transport and fate in variably-saturated soils appears invalid, except for highly sandy soils. The unified LIGA model with differing percolation thresholds for diffusion in the liquid and gaseous phases solves this problem. ; p. 1509-1517.
    Keywords: Clay ; Sandy Soils ; Bulk Density ; Solutes ; Mathematical Models ; Organic Matter ; Porosity ; Diffusivity
    ISSN: 0361-5995
    E-ISSN: 14350661
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  • 3
    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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  • 4
    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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  • 5
    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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  • 6
    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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  • 7
    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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  • 8
    Language: English
    In: Soil Science Society of America journal, 2012, Vol.76(3), pp.845-852
    Description: Subsurface gaseous-phase transport is governed by three gas transport parameters: the air permeability coefficient (k(a)), gas diffusion coefficient (D(P)), and gas dispersion coefficient (D(H)). Among these, D(H) is the least understood due to hitherto limited research into the relationship between gas dispersion and soil physical characteristics. In this study, a series of advection-dispersion experiments was performed on granular porous media to identify the effects of soil column dimensions (length and diameter), particle size and shape, dry bulk density, and moisture content on the magnitude of gas dispersion. Glass beads and various sands of different shapes (angular and rounded) with mean particle diameters (d(50)) ranging from 0.19 to 1.51 mm at both air-dry and variable moisture contents were used as granular porous media. Gas dispersion coefficients and gas dispersivities (α = D(H)/v, where v is the pore-gas velocity) were determined by fitting the advection-dispersion equation to the measured breakthrough curves. For all test conditions, D(H) increased linearly with v. The test results showed that neither soil column length nor diameter had significant effect on gas dispersivity. Under air-dry conditions, higher gas dispersivities were observed for media with wider particle size distribution and higher dry bulk density. The minor effect of particle shape on gas dispersivity was found under both air-dry and wet conditions. Under wet conditions, the variations in gas dispersivity were mainly controlled by the air-filled porosity. An empirical model was also proposed for the prediction of gas dispersivity in granular, unsaturated porous media. ; p. 845-852.
    Keywords: Soil Physical Properties ; Particle Size ; Sand ; Bulk Density ; Porous Media ; Prediction ; Equations ; Porosity ; Models ; Glass ; Water Content ; Air ; Permeability ; Particle Size Distribution ; Diffusivity
    ISSN: 0361-5995
    E-ISSN: 14350661
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  • 9
    Language: English
    In: Soil Science Society of America journal, 2012, Vol.76(6), pp.1946-1956
    Description: Modeling water distribution and flow in partially saturated soils requires knowledge of the soil water characteristic (SWC). However, measurement of the SWC is challenging and time-consuming and, in some cases, not feasible. This study introduces two predictive models (F(W)–model and A(W)–model) for the SWC, derived from readily available soil properties such as texture and bulk density. A total of 46 undisturbed soils from different horizons at 15 locations across Denmark were used for model evaluation. The F(W)–model predicts the volumetric water content as a function of volumetric fines content (organic matter and clay). It performed reasonably well for the dry-end of SWC (above a pF value of 2.0; pF = log(|ψ|), where ψ is the matric potential in cm), but did not do as well closer to saturated conditions. The A(W)–model predicts the volumetric water content as a function of volumetric content of different particle size fractions (organic matter, clay, silt, and fine and coarse sands). The volumetric content of a particular soil particle size fraction was considered if it contributed to the pore size fraction still occupied with water at the given pF value. Hereby, the A(W)–model implicitly assumes that a given particle size fraction creates an analogue pore size fraction and further this pore size fraction filled with water is corresponding to a certain pF value according to the well-known capillary rise equation. The A(W)–model was found to be quite robust, and it performed exceptionally well for pF values ranging from 0.4 to 4.2 for different soil types. For prediction of the continuous SWC, it is recommended to parameterize the van Genuchten model based on the SWC data points predicted by the A(W)–model. ; p. 1946-1956.
    Keywords: Clay ; Particle Size ; Soil Types ; Bulk Density ; Texture ; Prediction ; Capillarity ; Silt ; Equations ; Organic Matter ; Models ; Water Distribution ; Soil Water Characteristic ; Water Content ; Saturated Conditions
    ISSN: 0361-5995
    E-ISSN: 14350661
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  • 10
    Language: English
    In: Water, Air, & Soil Pollution, 2014, Vol.225(9), pp.1-13
    Description: Biochar, a by-product resulting from the pyrolysis of biomass, is considered to be an anthropogenic carbonaceous sorbent. Despite a worldwide increase in the application of biochar on agricultural fields to improve crop productivity over the past few decades, there have been few studies on their influences on the sorption of environmental contaminants. In a field-based study at two experimental sites in Denmark, we investigated the effect of birch wood-derived biochar ( Skogans kol ) on the sorption of phenanthrene in soils with different properties. The soil sorption coefficient, K d (L kg −1 ), of phenanthrene was measured on sandy loam and loamy sand soils which have received from zero up to 100 t ha −1 of biochar. Results show that birch wood biochar had a higher K d compared to soils. Furthermore, the application of birch wood biochar enhanced the sorption of phenanthrene in agricultural soils, and the enhancement effect increased with an increasing biochar application rate. Aging, repeated application, and higher clay content suppressed the biochar enhancement effect on the sorption of phenanthrene. Phenanthrene K d was found to be strongly and positively correlated with both total and non-complexed organic carbon, while negatively correlated with clay content. The results also revealed that biochar–mineral interactions play an important role in the sorption of phenanthrene in biochar-amended soil.
    Keywords: Phenanthrene ; Biochar ; Sorption ; Organic carbon
    ISSN: 0049-6979
    E-ISSN: 1573-2932
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