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  • 1
    Online Resource
    Online Resource
    An open Soil Structure Library based on X-ray CT data
    Copernicus GmbH ; 2022
    In:  SOIL Vol. 8, No. 2 ( 2022-07-29), p. 507-515
    Details
    In: SOIL, Copernicus GmbH, Vol. 8, No. 2 ( 2022-07-29), p. 507-515
    Abstract: Abstract. Soil structure in terms of the spatial arrangement of pores and solids is highly relevant for most physical and biochemical processes in soil. While this was known for a long time, a scientific approach to quantify soil structural characteristics was also missing for a long time. This was due to its buried nature but also due to the three-dimensional complexity. During the last two decades, tools to acquire full 3D images of undisturbed soil became more and more available and a number of powerful software tools were developed to reduce the complexity to a set of meaningful numbers. However, the standardization of soil structure analysis for a better comparability of the results is not well developed and the accessibility of required computing facilities and software is still limited. At this stage, we introduce an open-access Soil Structure Library (https://structurelib.ufz.de/, last access: 22 July 2022) which offers well-defined soil structure analyses for X-ray CT (computed tomography) data sets uploaded by interested scientists. At the same time, the aim of this library is to serve as an open data source for real pore structures as developed in a wide spectrum of different soil types under different site conditions all over the globe, by making accessible the uploaded binarized 3D images. By combining pore structure metrics with essential soil information requested during upload (e.g., bulk density, texture, organic carbon content), this Soil Structure Library can be harnessed towards data mining and development of soil-structure-based pedotransfer functions. In this paper, we describe the architecture of the Soil Structure Library and the provided metrics. This is complemented by an example of how the database can be used to address new research questions.
    Type of Medium: Online Resource
    ISSN: 2199-398X
    URL: Article
    URL: Article
    DOI: 10.5194/soil-8-507-2022
    DOI: 10.5194/soil-8-507-2022-supplement
    Language: English
    Publisher: Copernicus GmbH
    Publication Date: 2022
    detail.hit.zdb_id: 2834892-8
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  • 2
    Online Resource
    Online Resource
    Prediction of biopore- and matrix-dominated flow from X-ray CT-derived macropore network characteristics
    Copernicus GmbH ; 2016
    In:  Hydrology and Earth System Sciences Vol. 20, No. 10 ( 2016-10-06), p. 4017-4030
    Details
    In: Hydrology and Earth System Sciences, Copernicus GmbH, Vol. 20, No. 10 ( 2016-10-06), p. 4017-4030
    Abstract: Abstract. Prediction and modeling of localized flow processes in macropores is of crucial importance for sustaining both soil and water quality. However, currently there are no reliable means to predict preferential flow due to its inherently large spatial variability. The aim of this study was to investigate the predictive performance of previously developed empirical models for both water and air flow and to explore the potential applicability of X-ray computed tomography (CT)-derived macropore network characteristics. For this purpose, 65 cylindrical soil columns (6 cm diameter and 3.5 cm height) were extracted from the topsoil (5 cm to 8.5 cm depth) in a 15 m  ×  15 m grid from an agricultural field located in Silstrup, Denmark. All soil columns were scanned with an industrial X-ray CT scanner (129 µm resolution) and later employed for measurement of saturated hydraulic conductivity, air permeability at −30 and −100 cm matric potential, and gas diffusivity at −30 and −100 cm matric potential. Distribution maps for saturated hydraulic conductivity, air permeability, and gas diffusivity reflected no autocorrelation irrespective of soil texture and organic matter content. Existing empirical predictive models for saturated hydraulic conductivity and air permeability showed poor performance, as they were not able to realistically capture macropore flow. The tested empirical model for gas diffusivity predicted measurements at −100 cm matric potential reasonably well, but failed at −30 cm matric potential, particularly for soil columns with biopore-dominated flow. X-ray CT-derived macroporosity matched the measured air-filled porosity at −30 cm matric potential well. Many of the CT-derived macropore network characteristics were strongly interrelated. Most of the macropore network characteristics were also significantly correlated with saturated hydraulic conductivity, air permeability, and gas diffusivity. The predictive Ahuja et al. (1984) model for saturated hydraulic conductivity, air permeability, and gas diffusivity performed reasonably well when parameterized with novel, X-ray CT-derived parameters such as effective percolating macroporosity for biopore-dominated flow and total macroporosity for matrix-dominated flow. The obtained results further indicate that it is crucially important to discern between matrix-dominated and biopore-dominated flow for accurate prediction of macropore flow from X-ray CT-derived macropore network characteristics.
    Type of Medium: Online Resource
    ISSN: 1607-7938
    URL: Article
    URL: Article
    DOI: 10.5194/hess-20-4017-2016
    DOI: 10.5194/hess-20-4017-2016-supplement
    Language: English
    Publisher: Copernicus GmbH
    Publication Date: 2016
    detail.hit.zdb_id: 2100610-6
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  • 3
    Online Resource
    Online Resource
    Physical constraints for respiration in microbial hotspots in soil and their importance for denitrification
    Copernicus GmbH ; 2019
    In:  Biogeosciences Vol. 16, No. 18 ( 2019-09-27), p. 3665-3678
    Details
    In: Biogeosciences, Copernicus GmbH, Vol. 16, No. 18 ( 2019-09-27), p. 3665-3678
    Abstract: Abstract. Soil denitrification is the most important terrestrial process returning reactive nitrogen to the atmosphere, but remains poorly understood. In upland soils, denitrification occurs in hotspots of enhanced microbial activity, even under well-aerated conditions, and causes harmful emissions of nitric (NO) and nitrous oxide (N2O). The timing and magnitude of such emissions are difficult to predict due to the delicate balance of oxygen (O2) consumption and diffusion in soil. To study how spatial distribution of hotspots affects O2 exchange and denitrification, we embedded microbial hotspots composed of porous glass beads saturated with growing cultures of either Agrobacterium tumefaciens (a denitrifier lacking N2O reductase) or Paracoccus denitrificans (a “complete” denitrifier) in different architectures (random vs. layered) in sterile sand that was adjusted to different water saturations (30 %, 60 %, 90 %). Gas kinetics (O2, CO2, NO, N2O and N2) were measured at high temporal resolution in batch mode. Air connectivity, air distance and air tortuosity were determined by X-ray tomography after the experiment. The hotspot architecture exerted strong control on microbial growth and timing of denitrification at low and intermediate saturations, because the separation distance between the microbial hotspots governed local oxygen supply. Electron flow diverted to denitrification in anoxic hotspot centers was low (2 %–7 %) but increased markedly (17 %–27 %) at high water saturation. X-ray analysis revealed that the air phase around most of the hotspots remained connected to the headspace even at 90 % saturation, suggesting that the threshold response of denitrification to soil moisture could be ascribed to increasing tortuosity of air-filled pores and the distance from the saturated hotspots to these air-filled pores. Our findings suggest that denitrification and its gaseous product stoichiometry depend not only on the amount of microbial hotspots in aerated soil, but also on their spatial distribution. We demonstrate that combining measurements of microbial activity with quantitative analysis of diffusion lengths using X-ray tomography provides unprecedented insights into physical constraints regulating soil microbial respiration in general and denitrification in particular. This paves the way to using observable soil structural attributes to predict denitrification and to parameterize models. Further experiments with natural soil structure, carbon substrates and microbial communities are required to devise and parametrize denitrification models explicit for microbial hotspots.
    Type of Medium: Online Resource
    ISSN: 1726-4189
    URL: Article
    URL: Article
    DOI: 10.5194/bg-16-3665-2019
    DOI: 10.5194/bg-16-3665-2019-supplement
    Language: English
    Publisher: Copernicus GmbH
    Publication Date: 2019
    detail.hit.zdb_id: 2158181-2
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  • 4
    Online Resource
    Online Resource
    A systemic approach for modeling soil functions
    Copernicus GmbH ; 2018
    In:  SOIL Vol. 4, No. 1 ( 2018-03-15), p. 83-92
    Details
    In: SOIL, Copernicus GmbH, Vol. 4, No. 1 ( 2018-03-15), p. 83-92
    Abstract: Abstract. The central importance of soil for the functioning of terrestrial systems is increasingly recognized. Critically relevant for water quality, climate control, nutrient cycling and biodiversity, soil provides more functions than just the basis for agricultural production. Nowadays, soil is increasingly under pressure as a limited resource for the production of food, energy and raw materials. This has led to an increasing demand for concepts assessing soil functions so that they can be adequately considered in decision-making aimed at sustainable soil management. The various soil science disciplines have progressively developed highly sophisticated methods to explore the multitude of physical, chemical and biological processes in soil. It is not obvious, however, how the steadily improving insight into soil processes may contribute to the evaluation of soil functions. Here, we present to a new systemic modeling framework that allows for a consistent coupling between reductionist yet observable indicators for soil functions with detailed process understanding. It is based on the mechanistic relationships between soil functional attributes, each explained by a network of interacting processes as derived from scientific evidence. The non-linear character of these interactions produces stability and resilience of soil with respect to functional characteristics. We anticipate that this new conceptional framework will integrate the various soil science disciplines and help identify important future research questions at the interface between disciplines. It allows the overwhelming complexity of soil systems to be adequately coped with and paves the way for steadily improving our capability to assess soil functions based on scientific understanding.
    Type of Medium: Online Resource
    ISSN: 2199-398X
    URL: Article
    DOI: 10.5194/soil-4-83-2018
    Language: English
    Publisher: Copernicus GmbH
    Publication Date: 2018
    detail.hit.zdb_id: 2834892-8
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  • 5
    Online Resource
    Online Resource
    Responses of soil water storage and crop water use efficiency to changing climatic conditions: a lysimeter-based space-for-time approach
    Copernicus GmbH ; 2020
    In:  Hydrology and Earth System Sciences Vol. 24, No. 3 ( 2020-03-13), p. 1211-1225
    Details
    In: Hydrology and Earth System Sciences, Copernicus GmbH, Vol. 24, No. 3 ( 2020-03-13), p. 1211-1225
    Abstract: Abstract. Future crop production will be affected by climatic changes. In several regions, the projected changes in total rainfall and seasonal rainfall patterns will lead to lower soil water storage (SWS), which in turn affects crop water uptake, crop yield, water use efficiency (WUE), grain quality and groundwater recharge. Effects of climate change on those variables depend on the soil properties and were often estimated based on model simulations. The objective of this study was to investigate the response of key variables in four different soils and for two different climates in Germany with a different aridity index (AI): 1.09 for the wetter (range: 0.82 to 1.29) and 1.57 for the drier (range: 1.19 to 1.77) climate. This is done by using high-precision weighable lysimeters. According to a “space-for-time” (SFT) concept, intact soil monoliths that were moved to sites with contrasting climatic conditions have been monitored from April 2011 until December 2017. Evapotranspiration (ET) was lower for the same soil under the relatively drier climate, whereas crop yield was significantly higher, without affecting grain quality. Especially “non-productive” water losses (evapotranspiration out of the main growing period) were lower, which led to a more efficient crop water use in the drier climate. A characteristic decrease of the SWS for soils with a finer texture was observed after a longer drought period under a drier climate. The reduced SWS after the drought remained until the end of the observation period which demonstrates carry-over of drought from one growing season to another and the overall long-term effects of single drought events. In the relatively drier climate, water flow at the soil profile bottom showed a small net upward flux over the entire monitoring period as compared to downward fluxes (groundwater recharge) or drainage in the relatively wetter climate and larger recharge rates in the coarser- as compared to finer-textured soils. The large variability of recharge from year to year and the long-lasting effects of drought periods on the SWS imply that long-term monitoring of soil water balance components is necessary to obtain representative estimates. Results confirmed a more efficient crop water use under less-plant-available soil moisture conditions. Long-term effects of changing climatic conditions on the SWS and ecosystem productivity should be considered when trying to develop adaptation strategies in the agricultural sector.
    Type of Medium: Online Resource
    ISSN: 1607-7938
    URL: Article
    URL: Article
    DOI: 10.5194/hess-24-1211-2020
    DOI: 10.5194/hess-24-1211-2020-supplement
    Language: English
    Publisher: Copernicus GmbH
    Publication Date: 2020
    detail.hit.zdb_id: 2100610-6
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  • 6
    Online Resource
    Online Resource
    Denitrification in soil as a function of oxygen availability at the microscale
    Copernicus GmbH ; 2021
    In:  Biogeosciences Vol. 18, No. 3 ( 2021-02-16), p. 1185-1201
    Details
    In: Biogeosciences, Copernicus GmbH, Vol. 18, No. 3 ( 2021-02-16), p. 1185-1201
    Abstract: Abstract. The prediction of nitrous oxide (N2O) and of dinitrogen (N2) emissions formed by biotic denitrification in soil is notoriously difficult due to challenges in capturing co-occurring processes at microscopic scales. N2O production and reduction depend on the spatial extent of anoxic conditions in soil, which in turn are a function of oxygen (O2) supply through diffusion and O2 demand by respiration in the presence of an alternative electron acceptor (e.g. nitrate). This study aimed to explore controlling factors of complete denitrification in terms of N2O and (N2O + N2) fluxes in repacked soils by taking micro-environmental conditions directly into account. This was achieved by measuring microscale oxygen saturation and estimating the anaerobic soil volume fraction (ansvf) based on internal air distribution measured with X-ray computed tomography (X-ray CT). O2 supply and demand were explored systemically in a full factorial design with soil organic matter (SOM; 1.2 % and 4.5 %), aggregate size (2–4 and 4–8 mm), and water saturation (70 %, 83 %, and 95 % water-holding capacity, WHC) as factors. CO2 and N2O emissions were monitored with gas chromatography. The 15N gas flux method was used to estimate the N2O reduction to N2. N gas emissions could only be predicted well when explanatory variables for O2 demand and O2 supply were considered jointly. Combining CO2 emission and ansvf as proxies for O2 demand and supply resulted in 83 % explained variability in (N2O + N2) emissions and together with the denitrification product ratio [N2O / (N2O + N2)] (pr) 81 % in N2O emissions. O2 concentration measured by microsensors was a poor predictor due to the variability in O2 over small distances combined with the small measurement volume of the microsensors. The substitution of predictors by independent, readily available proxies for O2 demand (SOM) and O2 supply (diffusivity) reduced the predictive power considerably (60 % and 66 % for N2O and (N2O+N2) fluxes, respectively). The new approach of using X-ray CT imaging analysis to directly quantify soil structure in terms of ansvf in combination with N2O and (N2O + N2) flux measurements opens up new perspectives to estimate complete denitrification in soil. This will also contribute to improving N2O flux models and can help to develop mitigation strategies for N2O fluxes and improve N use efficiency.
    Type of Medium: Online Resource
    ISSN: 1726-4189
    URL: Article
    URL: Article
    DOI: 10.5194/bg-18-1185-2021
    DOI: 10.5194/bg-18-1185-2021-supplement
    Language: English
    Publisher: Copernicus GmbH
    Publication Date: 2021
    detail.hit.zdb_id: 2158181-2
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