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  • 1
    Language: English
    In: Geoderma, April 2014, Vol.217-218, pp.181-189
    Description: The study characterized soil structure development and evolution in six plots that were amended with varying amounts of animal manure (AM) and NPK fertilizer over a period of 106 years in a long-term fertilization experiment in Bad Lauchstädt, Germany. Two intact soil cores (10-cm diameter and 8-cm tall) and bulk soil samples were extracted from a depth between 5 and 15-cm from each plot. Soil properties including texture, organic carbon, soil–water characteristic, air permeability and diffusivity were measured and analyzed along with X-ray computed tomography (CT) data. Long-term applications of AM and NPK had a major impact on soil organic carbon content which increased from 0.015 kg kg (unfertilized plot) to 0.024 kg kg (well fertilized plot, 30 T ha 2y AM with NPK). Total porosity linearly followed the organic carbon gradient, increasing from 0.36 to 0.43 m m . The water holding capacity of the soil was considerably increased with the increase of AM and NPK applications. Gas diffusivity and air permeability measurements clearly indicated that the level of soil aeration improved with increasing AM and NPK fertilizer amount. The three-dimensional X-ray CT visualizations revealed higher macroporosity and biological (earthworm) activity in the well fertilized areas when compared to plots without or only a small amount of fertilizer applied. A combined evaluation of the soil water characteristic, gas transport and X-ray CT results suggested that pore size distributions widened, and pore connectivity was significantly improved with increasing fertilizer amount. Furthermore, the soils fertilized with both AM and NPK showed a more aggregated structure than soils amended with AM only.
    Keywords: Animal Manure ; Npk Fertilizers ; Soil–Water Characteristic ; Gas Diffusivity ; Air Permeability ; X-Ray Computed Tomography ; Agriculture
    ISSN: 0016-7061
    E-ISSN: 1872-6259
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  • 2
    Language: English
    In: Geoderma, 01 July 2019, Vol.345, pp.63-71
    Description: Soil structure is not static but undergoes continuous changes due to a wide range of biotic and abiotic drivers such as bioturbation and the mechanical disturbance by tillage. This continuous alteration of soil structure beyond the pure swelling and shrinking of some stable structure is what we refer to as soil structure dynamics. It has important consequences for carbon turnover in soil as it controls how quickly soil organic matter gets occluded from or exposed to mineralization. So far there are hardly any direct observations of the rate at which soil pores are formed and destroyed. Here we employ are recently introduced labeling approach for soil structure that measures how quickly the locations of small garnet particles get randomized in soil as a measure for soil structure dynamics. We investigate the effect of desiccation crack dynamics on pore space attributes in general and soils structure turnover in particular using X-ray microtomography for repeated wetting-drying cycles. This is explored for three different soils with a range of soil organic matter content, clay content and different clay mineralogy that were sieved to a certain aggregate size fraction (0.63–2 mm) and repacked at two different bulk density levels. The total magnitude of desiccation crack formation mainly depended on the clay content and clay mineralogy. Higher soil organic matter content led to a denser crack pattern with smaller aperture. Wetting-drying cycles did not only effect visible macroporosity (〉8 μm), but also unresolved mesoporosity. The changes in macroporosity were higher at lower bulk density. Most importantly, repeated wetting-drying cycles did not lead to a randomization of distances between garnet particles and pores. This demonstrates that former failure zones are reactivated during subsequent drying cycles. Hence, wetting-drying resulted in reversible particle displacement and therefore would not have triggered the exposure of occluded carbon that was not already exposed during the previous drying event.
    Keywords: Soil Structure ; Desiccation Cracks ; X-Ray Tomography ; Macropores ; Clay Mineralogy ; Carbon Turnover ; Agriculture
    ISSN: 0016-7061
    E-ISSN: 1872-6259
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  • 3
    Language: English
    In: Geoderma, 15 July 2019, Vol.346, pp.52-62
    Description: Some soil physical properties can easily be measured using classical laboratory methods. However, explicit valuable information on the real morphology of the pore structure as well as soil physical properties cannot be obtained at the same time with classical methods. This requires non-destructive measurements such as X-ray computed tomography (CT). However, explicit valuable information on the real morphology of the pore structure as well as soil physical properties cannot be obtained at the same time with classical methods. This paper combines parameters obtained from CT analysis (mean macropore diameter, macroporosity, pore connectivity, anisotropy) and classical laboratory methods (dry bulk and aggregate density, saturated hydraulic conductivity, mechanical precompression stress) to analyse soil compaction, exemplified on samples from two tillage treatments (cultivator and plough) and at two moisture states (6 and 1000 kPa matric potential) on a Chernozem collected at a soil depth of 16–22 cm (texture 0–30 cm: silty clay loam). The study shows that the matric potential can have a decisive impact on the mechanical stability of soil. In the loose but less stable plough treatment a more negative matric potential was clearly beneficial to the mechanical stability. In already dense soil structures, as in the cultivator treatment, a reduction of water content was less effective in increasing soil stability. The CT parameters were all closely and uniquely related to each other. The shown CT parameters can be used for a standardized characterization of the soil. Ploughing has a positive effect on soil structure which persists only as long as macroporosity and mean macropore diameter remain high. Plough maintains higher pore connectivity when compacted under dry conditions.
    Keywords: X-Ray CT ; Mechanical Soil Analysis ; Conservation Tillage ; Conventional Tillage ; Soil Compaction ; Precompression Stress ; Agriculture
    ISSN: 0016-7061
    E-ISSN: 1872-6259
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  • 4
    Language: English
    In: Geoderma, 01 January 2019, Vol.333, pp.90-98
    Description: Secondary treated wastewater, a commonly used water resource in agriculture in (semi-)arid areas, often contains salts, sodium, and organic matter which may affect soil structure and hydraulic properties. The main objective of this study was to jointly analyse the effects of long-term irrigation with treated wastewater on physicochemical soil characteristics, soil structure, and soil water dynamics in undisturbed soils. X-ray microtomography was used to determine changes in macro-porosity (〉 19 μm), pore size distribution, and pore connectivity of a sandy clay loam and a loamy sand. Differences in the pore network among soils irrigated with treated wastewater, fresh water that replaced treated wastewater, and non-irrigated control plots could be explained by changes in textural composition, soil physicochemical parameters, and hydraulic properties. In this study we showed that irrigation led to the development of a connected macro-pore network, independent of the studied water quality. The leaching of silt and clay particles in the sandy soil due to treated wastewater irrigation resulted in an increase of pores 〈 130 μm. While this change in texture reduced water retention, the unsaturated hydraulic conductivity was diminished by physicochemical alteration, i.e. induced water repellency and clay mineral swelling. Overall, the fine textured sandy clay loam was much more resistant to soil alteration by treated wastewater irrigation than the loamy sand.
    Keywords: Soil Structure ; Treated Wastewater Irrigation ; Clay Dispersion ; Unsaturated Hydraulic Conductivity ; Soil Water Retention ; X-Ray Microtomography ; Agriculture
    ISSN: 0016-7061
    E-ISSN: 1872-6259
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