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  • Arthur, Emmanuel  (29)
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  • 1
    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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  • 2
    Language: English
    In: Agriculture, Ecosystems and Environment, Sept 15, 2012, Vol.159, p.9(10)
    Description: To link to full-text access for this article, visit this link: http://dx.doi.org/10.1016/j.agee.2012.06.021 Byline: Emmanuel Arthur (a), Per Moldrup (b), Martin Holmstrup (c), Per Schjonning (a), Anne Winding (d), Philipp Mayer (d), Lis W. de Jonge (a) Keywords: Soil contamination; Dehydrogenase activity; Clay dispersibility; Air permeability; Compression; Resilience Abstract: a* Microbial activity decreased significantly at copper concentration [approximately equal to]500mgkg.sup.-1. a* Soil compression resistance had an increasing trend with copper concentration. a* Copper contaminated soils had higher amounts of water dispersible clay. a* Clay dispersibility correlated with microbial activity in a copper contaminated field. Author Affiliation: (a) Department of Agroecology, Faculty of Science and Technology, Aarhus University, Blichers Alle 20, P.O. Box 50, DK-8830 Tjele, Denmark (b) Department of Biotechnology, Chemistry and Environmental Engineering, Aalborg University, Sohngaardsholmsvej 57, DK-9000 Aalborg, Denmark (c) Department of Bioscience, Aarhus University, Vejlsovej 25, DK-8600 Silkeborg, Denmark (d) Department of Environmental Science, Faculty of Science and Technology, Aarhus University. Frederiksborgvej 399, DK-4000 Roskilde, Denmark Article History: Received 23 February 2012; Revised 1 June 2012; Accepted 15 June 2012
    Keywords: Soil Pollution ; Permeability ; Soil Microbiology ; Universities And Colleges
    ISSN: 0167-8809
    Source: Cengage Learning, Inc.
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  • 3
    Language: English
    In: Journal of Hydrology, 2015, Vol.521, p.498(10)
    Description: To link to full-text access for this article, visit this link: http://dx.doi.org/10.1016/j.jhydrol.2014.12.018 Byline: Dan Karup Jensen, Markus Tuller, Lis W. de Jonge, Emmanuel Arthur, Per Moldrup Abstract: * We present a new approach to predict the entire SWC using limited data. * The approach considers capillarity and adsorptive contributions to obtain the SWC. * We obtained accurate prediction of SWC regardless of soil texture. * Clay, silt and organic matter contribute significantly to water adsorption. Article History: Received 23 July 2014; Revised 10 December 2014; Accepted 11 December 2014 Article Note: (miscellaneous) This manuscript was handled by Peter K. Kitanidis, Editor-in-Chief, with the assistance of J. Simunek, Associate Editor
    Keywords: Soil Moisture
    ISSN: 0022-1694
    Source: Cengage Learning, Inc.
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  • 4
    Language: English
    In: Journal of Hydrology, February 2015, Vol.521, pp.498-507
    Description: The present study proposes a new two-step approach to prediction of the continuous soil water characteristic (SWC) from saturation to oven-dryness from a limited number of measured textural data, organic matter content and dry bulk density. The approach combines dry- and wet-region functions to obtain the entire SWC by means of parameterizing a previously developed continuous equation. The dry region function relates gravimetric soil fractions to adsorptive forces and the corresponding water adsorbed to soil particles. The wet region function converts the volumetric particle size fractions to pore size fractions and utilizes the capillary rise equation to predict water content and matric potential pairs. Twenty-one Arizona source soils with clay and organic carbon contents ranging from 0.01 to 0.52 kg kg and 0 to 0.07 kg kg , respectively, were used for the model development. The SWCs were measured with Tempe cells, a WP4-T Dewpoint Potentiameter, and a water vapor sorption analyzer (VSA). The model was subsequently tested for eight soils from various agricultural fields in Denmark with clay contents ranging from 0.05 to 0.41 kg kg . Test results clearly revealed that the proposed model can adequately predict the SWC based on limited soil data. The advantage of the new model is that it considers both capillary and adsorptive contributions to obtain the SWC from saturation to oven-dryness.
    Keywords: Capillarity ; Adsorption ; Unsaturated Soil ; Water Retention ; Soil Moisture ; Geography
    ISSN: 0022-1694
    E-ISSN: 1879-2707
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  • 5
    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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  • 6
    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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  • 7
    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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  • 8
    Language: English
    In: Soil Science Society of America Journal, May-June, 2014, Vol.78(3), p.754(7)
    Description: The characterization and description of important soil processes such as water vapor transport, volatilization of pesticides, and hysteresis require accurate means for measuring the soil water characteristic (SWC) at low water potentials. Until recently, measurement of the SWC at low water potentials was constrained by hydraulic decoupling and long equilibration times when pressure plates or single-point, chilled-mirror instruments were used. A new, fully automated vapor sorption analyzer (VSA) helps to overcome these challenges and allows faster measurement of highly detailed water vapor sorption isotherms. In this technical note we present a comprehensive evaluation of the VSA instrument for a wide range of differently textured soils and discuss optimal measurement settings. The effects of operation mode, air-flow rate, sample pretreatment, test temperature, sample mass, and mass trigger point on resultant sorption isotherms were evaluated for a relative humidity (RH) range from 0.10 to 0.90. Both adsorption and desorption branches were measured for all soils within a reasonable time period (10-50 h). Sample masses larger than 3.5 g resulted in incomplete adsorption and desorption, while oven-dry (105[degrees]C) samples of coarse-textured soils exhibited water repellency characteristics. The required measurement times were strongly correlated with clay content and influenced by high organic carbon content.
    Keywords: Water Vapor -- Measurement ; Volatilization (Physics) -- Research ; Soil Research
    ISSN: 0361-5995
    E-ISSN: 14350661
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  • 9
    In: Soil Science Society of America Journal, January 2012, Vol.76(1), pp.18-27
    Description: Accurate estimation of soil gas diffusivity (/, the ratio of gas diffusion coefficients in soil and free air) and air permeability () 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, / and 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 were used to characterize particle and pore size distributions, respectively. Campbell yielded a wide interval (4.6–26.2) and was highly correlated with α, β, and volumetric clay content. Both / and followed simple power‐law functions (PLFs) of air‐filled porosity (ε). The PLF tortuosity–connectivity factors (*) for / and were both highly correlated with all basic soil characteristics, in the order of volumetric clay content = Campbell 〉 gravimetric clay content 〉 α 〉 β. The PLF water blockage factors () for / and were also well (but relatively more weakly) correlated with the basic soil characteristics, again with the best correlations to volumetric clay content and . As a first attempt at developing a simple / model useful at the field scale, we extended the classical Buckingham / model (ε) by a scaling factor based on volumetric clay content. The scaled Buckingham model provided accurate predictions of (ε)/ across both natural clay gradients.
    Keywords: Soils ; Aarup Denmark ; Arhus Denmark ; Buckingham Model ; Cambisols ; Connectivity ; Convection ; Denmark ; Diffusivity ; Europe ; Experimental Studies ; Gas Transport ; Grain Size ; Jutland ; Laboratory Studies ; Luvisols ; Nordjylland Denmark ; Northern Denmark ; Particles ; Porosity ; Rosin-Rammler Model ; Saeby Denmark ; Scandinavia ; Size Distribution ; Soil Gases ; Soils ; Tortuosity ; Transport ; Western Europe;
    ISSN: 0361-5995
    E-ISSN: 1435-0661
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  • 10
    Language: English
    In: Soil Science Society of America Journal, March, 2013, Vol.77(2), p.362(10)
    Description: Understanding soil-gas phase properties and processes is important for finding solutions to critical environmental problems such as greenhouse gas emissions and transport of gaseous-phase contaminants in soils. Soil-air permeability, ka (?m2), is the key parameter governing advective gas movement in soil and is controlled by soil physical characteristics representing soil texture and structure. Models predicting ka as a function of air-filled porosity (?) often use a reference-point measurement, for example, ka,1000 at ?1000 (where the measurement is done at a suction of -1000 cm H2O). Using ka measurements from two Danish arable fields, each located on natural clay gradients, this study presents a pore tortuosity-disconnectivity analysis to characterize the soil-gas phase. The main objective of this study is to investigate the effect of soil-moisture condition, clay content, and other potential drivers of soil texture and structure on soil-gas phase characteristics based on a ka-based pore tortuosity parameter, Xa [= log(ka/ka,1000)/log(?/?,1000)]. Results showed that Xa did not vary significantly with soil matric potential (in the range of -10 to -1000 cm H2O), but the average Xa across moisture conditions showed a strong linear relation (R2 = 0.74) to clay content. The Xa, further showed promising relations to specific surface area, Rosin-Rammler particle size distribution indices, ? and ? (representing characteristic particle size and degree of sorting, respectively), and the Campbell water retention parameter, b. Considering clay as a main driver of soil-gas phase characteristics, we developed expressions linking clay content and ka,1000 at ?1000 and discussed the effect of clay content on general ka-? behavior.
    Keywords: Grading (Building materials) -- Usage ; Soil Permeability -- Analysis ; Soil Research
    ISSN: 0361-5995
    E-ISSN: 14350661
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