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See detailContribution à l'exploration de la structure des sols par microtomographie aux rayons X : vers une amélioration de la modélisation hydropédologique
Beckers, Eléonore ULg

Doctoral thesis (2014)

The aim of this thesis is to tend towards a better representation of soil water horizontal fluxes in hydropedological modelling. Tillage practices result in soil structural modifications which impact soil ... [more ▼]

The aim of this thesis is to tend towards a better representation of soil water horizontal fluxes in hydropedological modelling. Tillage practices result in soil structural modifications which impact soil hydrodynamic behaviour. This study takes place in this context, aiming to understand these modifications using X-ray microtomography (µCT), which allows a more fundamental analysis of soil. Indeed, this tool becomes a key in the field of soil science, giving a direct insight of the internal structure of soil. Besides, anisotropy studies are still rare as tiresome, and this work shows that the current hydrological models are anyway unable to represent it correctly: when it is taken into account, it rests on the hypothesis of a simple ratio between vertical and horizontal conductivity functions. First, microtomography is used supplementary to usual methods for the establishment of hydrodynamic functions near saturation. We showed that the retention curve designed with µCT information is more realistic since it leads to a better estimation of unsaturated hydraulic conductivity. However, these results could be doubtful depending on the different µCT acquisition or processing choices and hypothesis. Particularly, the thresholding step is crucial. Consequently, we propose a new global thresholding method based on the visible part of soil sample porosity. This method has been tested and validated in the context of the present study. This step allows us to use microtomography results to increase our knowledge of soil structure. A principal component analysis on soil pores structural parameters confirms that connectivity, specific surface, volume and radius are key factors for the differentiation of soil horizons texturally similar but structurally different. Our results show that structural parameters have to be taken into account to improve hydropedological modelling, especially if pores orientation is considered. We described thus the relevant parameters that can be obtained with µCT and which could help to better model water fluxes in soil while discussing the remaining limits and uncertainties, about upscaling issues notably. [less ▲]

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See detailCoupling X-ray microtomography and macroscopic soil measurements: a method to enhance near saturation functions?
Beckers, Eléonore ULg; Plougonven, Erwan; Gigot, Nicolas et al

in Hydrology & Earth System Sciences (2014), 18

Agricultural management practices influence soil structure, but the characterization of these modifications and consequences are still not completely understood. In this study, we aim at improving water ... [more ▼]

Agricultural management practices influence soil structure, but the characterization of these modifications and consequences are still not completely understood. In this study, we aim at improving water retention and hydraulic conductivity curves using both classical soil techniques and X-ray microtomography in the context of tillage simplification. We show a good match for retention and conductivity functions between macroscopic measurements and microtomographic information. Microtomography highlights the presence of a secondary pore system. Analysis of structural parameters for these pores appears to be significant and offers additional clues for objects differentiation. We show that relatively fast scans supply not only good results, but also enhance near saturation characterization, making microtomography a highly competitive instrument for routine soil characterization. [less ▲]

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See detailX-ray microtomography: A porosity-based thresholding method to improve soil pore network characterization?
Beckers, Eléonore ULg; Plougonven, Erwan ULg; Roisin, Christian et al

in Geoderma (2014), 219-220

X-ray microtomography, through quantification of soil structure at the microscale, could greatly facilitate the current understanding of soil hydrodynamic behaviour. However, binarisation method and ... [more ▼]

X-ray microtomography, through quantification of soil structure at the microscale, could greatly facilitate the current understanding of soil hydrodynamic behaviour. However, binarisation method and processing choices are subjective and can have a strong impact on results and conclusions. In this study, we test a new method based on the porosity detectable by X-ray microtomography, while validation is achieved through comparison of soil microtomogram information with soil physical measurements. These measurements consist of water retention and unsaturated hydraulic conductivity using two different soil populations with only structural differences. To assess the porosity-based method performances, we compare it to four other methods, namely the global method of Otsu and three recent soil-dedicated local methods. The robustness of the porosity-based method is also tested in regard to different pre-processing procedures. In this paper we demonstrate that soil segmentation through a porosity-based method is an interesting issue. Indeed, it is less demanding in terms of time and computational requirements than its alternatives, and combines robustness and performances broadly comparable with the recent local methods. [less ▲]

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See detailMicro and macroscopic investigation to quantify tillage impact on soil hydrodynamic behaviour
Beckers, Eléonore ULg; Roisin, Chrsitian; Plougonven, Erwan ULg et al

in Geophysical Research Abstracts (2012), 14

Nowadays, tillage simplification is an increasing practice. Many advantages are cited in the literature, such as energy saving, soil conservation etc. Agricultural management practices influence soil ... [more ▼]

Nowadays, tillage simplification is an increasing practice. Many advantages are cited in the literature, such as energy saving, soil conservation etc. Agricultural management practices influence soil structure, but consequent changes in soil hydrodynamic behaviour at the field scale are still not well understood. Many studies focus only on macroscopic measurements which do not provide mechanistic explanations. Moreover, research shows divergent conclusions over structure modification. The aim of this work is to fill this gap by quantifying soil structure modification depending on tillage intensity through both macroscopic and microscopic measurements, the latter improving our comprehension of the fundamental mechanisms involved. [less ▲]

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See detailANALYSES DE PROPRIÉTÉS HYDROPHYSIQUES D’UN SOL AGRICOLE SOUMIS À DIFFÉRENTS TRAITEMENTS CULTURAUX DANS LE CADRE DU PROJET SOLRESIDUS
Beekkerk van Ruth, Jöran ULg; Beckers, Eléonore ULg; Aubinet, Marc ULg et al

Conference (2011, May 06)

Le projet SOLRESIDUS est une collaboration entre diverses unités au sein de GxABT. Il vise à analyser l’impact du mode de travail du sol (labour/non labour, restitution/exportation des pailles) sur divers ... [more ▼]

Le projet SOLRESIDUS est une collaboration entre diverses unités au sein de GxABT. Il vise à analyser l’impact du mode de travail du sol (labour/non labour, restitution/exportation des pailles) sur divers paramètres édaphiques/culturaux d’un champ de blé d’hiver (parcelles du Bordia). Le but du projet est de fournir une approche multidisciplinaire à l’analyse de systèmes agricoles. Afin de favoriser l’interaction entre les différentes unités, une base de données regroupant les différents résultats et méthodologies sera créée. Plus spécifiquement, les mesures touchant aux systèmes Eau-Sol (Unités d’Hydrologie et de Physique) incluent des courbes de rétention (pF), des évaluations d’infiltrabilité (tensio-infiltromètres, anneaux), des profils d’humidité (manuels et automatiques) et une caractérisation de la macro et microstructure porale (scan 3D par tomographie à rayons X). Ces mesures seront faites tout au long du projet (2 ans), afin d’établir une base solide à la compréhension du comportement hydrophysique d’un sol agricole limoneux. Ceci inclut un suivi des paramètres lors de l’évolution de la culture, mais également une comparaison entre les modalités. [less ▲]

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See detailANALYSING THE SOIL STRUCTURE UNDER DIFFERENT TILLAGE SYSTEMS USING X-RAY MICROTOMOGRAPHY AND PF CURVES
Beekkerk van Ruth, Jöran ULg; Degre, Aurore ULg; Aubinet, Marc ULg et al

Poster (2011, February 23)

Assessing soil structure is primordial when comparing tillage systems. Whilst most conventional techniques characterize global parameters, X-ray microtomography allows a characterization of the poral ... [more ▼]

Assessing soil structure is primordial when comparing tillage systems. Whilst most conventional techniques characterize global parameters, X-ray microtomography allows a characterization of the poral space at a µm-scale. These results, combined with data from pF curves, can form a solid basis in order to quantify soil physical fertility. Soil samples were taken from the organic topsoil on two Belgian experimental sites implementing both conventional tillage (CT, ploughing) and simplified tillage (ST, superficial works), without straw restitution: Gentinnes, Brabant Wallon (March 2010), and Gembloux, Namur (November 2010). On the Gentinnes site (Aba(b)1), CT and ST have been implemented since October 2005, with a beet/winter wheat rotation. On the Gembloux site (Aba(b)), CT and ST have been implemented since September 2008, with a winter wheat cultivation since end 2009. Tomography (10 samples for Gentinnes, 8 for Gembloux) and pF curves (10 samples for Gentinnes, 14 for Gembloux) were used for analysis. Pressure pans were used in order to obtain the pF curves on 100 cm³ undisturbed samples. Soil cores (3 cm diameter, 5 cm height) were scanned using a Skyscan-1172 µ-CT device. The conical beam, operating at 100 kV, produced images having a 17µm pixel size, using a 16-bit 1048×2000 pixels camera equipped with an aluminium filter. The raw images were then treated under Matlab® for binarization, using a thresholding loop to fit the measured and the calculated porosity of each sample (Beckers et al, 2011). The 2D binary images were then analyzed under Matlab® and Skyscan™ CT-analyzer. On the site of Gentinnes, pF analysis showed a greater available water content (between pF 4.2 and 2.5) for ST, and a greater efficient porosity (between saturation and pF 2.5) for CT. The differences in available water content, although not significant, were confirmed by site observation. Tomography analysis yielded the following: under ST, the pores are smaller and the anisotropy less developed. As for the poral connectivity, it was found greater in CT. On the site of Gembloux, however, no significant differences were found between the tillage systems concerning the pF curves. Tomography analysis showed smaller pores for simplified tillage, but the differences deduced by the tomographic analysis of the Gentinnes samples concerning connectivity and anisotropy were not found in this case. To conclude, from the results, the soil structure is found to differ between CT and ST. The pores tend to be smaller and less oriented in ST, whilst in CT pores are more connected. Soils undergoing a CT show a greater efficient porosity, whilst soils under ST display a greater available water content. However, these differences were mostly spotted on the Gentinnes site: in Gembloux, the differences between the samples were less marked. This could be due to the fact that the soil did not have time to differentiate yet (less than 3 years of tillage differentiation). More sampling is needed in any case before inferring general conclusions from these observations. A further analysis of the soil images, especially concerning pore orientation, will be done in order to fully exploit the tomography results. [less ▲]

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See detailL’hydrologie, une partenaire de la géomorphopédologie pour une gestion transéchelle des grands enjeux environnementaux
Degre, Aurore ULg; Sohier, Catherine ULg; Colard, François ULg et al

in Biotechnologie, Agronomie, Société et Environnement = Biotechnology, Agronomy, Society and Environment [=BASE] (2011), S2(15), 699-707

Unsaturated soil and subsoil are often called “critical zone” considering their major interfacing role in our environment. Dealing with solute transfer or water and soil conservation, hydrologic research ... [more ▼]

Unsaturated soil and subsoil are often called “critical zone” considering their major interfacing role in our environment. Dealing with solute transfer or water and soil conservation, hydrologic research relies on pedologic descriptions. It is the case from micro to macro scale analysis. Hydrodynamic parameters are derived from pedologic information on soil. They allow hydrologists to quantify and spatially describe the dynamic exchanges between water, soil, crops and atmosphere. The modelling of water and solute transfer through soil and vadose zone also needs them. The paper presents some research highlights on soil behaviour, hydrological modelling and forecasting under climate change. Erosion is another major topic. Soil is a poorly renewable resource. Soil conservation and soft hydraulic management in watersheds deserve more attention. They can help limiting nutrient and sediment transfer to surface water. Again, pedologic information is the starting point of conceptualization and modelling. Furthermore, the Soil Map of Belgium includes information on geomorphology and landscape descriptions which date from decades. They are of first importance to calibrate and validate detachment, transport and sedimentation models. In the current context of high environmental concern, it is demonstrated how hydrology and pedology have to be partners in order to deal with such major issues. [less ▲]

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See detailEffects of different spatial interpolators on the estimate of extreme precipitations
Ly, Sarann ULg; Beckers, Eléonore ULg; Charles, Catherine ULg et al

in Geophysical Research Abstracts (2011), 13

The design values of the areal precipitation are needed for engineer to manage vital elements of our infrastructure. The areal precipitation can be generated by different interpolation methods. The ... [more ▼]

The design values of the areal precipitation are needed for engineer to manage vital elements of our infrastructure. The areal precipitation can be generated by different interpolation methods. The problem involves choosing the interpolation method that we should use to estimate the extreme event. This work aimed at analyzing the effects of different interpolation methods on the estimate of extreme events of daily areal precipitations at catchment scale. The extreme rainfalls were estimated using areal daily rainfall interpolated by several interpolation methods (Thiessen polygon, Inverse Distance Weighting, Ordinary Kriging, Universal Kriging, Kriging with an External Drift and Ordinary Cokriging). We used thirty-years-long daily time series and different density of rain gages (from 4 to 70 rain gages). Our study is located in the Ourthe and Ambleve catchment area (2908 km²) in the southern part of Belgium). Spatial interpolation with the geostatistical and Inverse Distance Weighting algorithms outperformed considerably interpolation with the Thiessen polygon. Kriging with an External Drift and Ordinary Cokriging presented the highest Root Mean Square Error between the geostatistical and Inverse Distance Weighting methods. Ordinary Kriging and Inverse Distance Weighting were considered to be the best methods, as they provided smallest Root Mean Square Error for nearly all cases. However, it’s not really the case of extreme estimates for particular return period. The extreme daily rainfall, corresponding to return periods of 25, 50 and 100 years, were computed by fitting of a statistical model to the series of maximum annual precipitation. These estimates were conducted using HYFRAN which allows us to fit 16 different statistical models, in 2 or 3 parameters. The most known are the models of Gumbel, Gamma, Weibull, exponential, Pareto, lognormale, Pearson III and GEV. Our results showed that the behaviour of extreme daily areal rainfall in this area was best described via the Gumbel and lognormal distributions. Using 70 rain gages, little differences in extreme rainfall were observed between the interpolation methods. The estimates from these methods were in the area of 95% confidence intervals of the estimates using the Thiessen polygon. However, when the number of rain gages diminishes, the Universal Kriging and Kriging with External drift methods produced extreme estimates outside the area of 95% confidence intervals of the estimates using the Thiessen polygon with all available stations. The analysis described here provides a means to choose the interpolation method in view to calculate extreme events. It shows to engineers or hydrologists the need for a particular care when working in the regions of sparse data. [less ▲]

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See detailRevue bibliographique : la prise en compte des transferts horizontaux dans les modèles hydrologiques
Beckers, Eléonore ULg; Degre, Aurore ULg

in Biotechnologie, Agronomie, Société et Environnement = Biotechnology, Agronomy, Society and Environment [=BASE] (2011), 15(1), 143-151

This bibliographical review sums up the different schemes in hydrological modelling. Moreover, it underlines how the interflows are taken into account and draws the first lines to improve their physically ... [more ▼]

This bibliographical review sums up the different schemes in hydrological modelling. Moreover, it underlines how the interflows are taken into account and draws the first lines to improve their physically based representation. In the mood of the change in agricultural practices, especially concerning the conventional tillage reduction in support of conservational tillage, it seems to be necessary to propose a better description of decisive parameters like horizontal hydraulic conductivity. More precisely, the dependence of this parameter with the water retention curve has to be described in order to represent fluxes at the plot scale and at the watershed scale. Under these circumstances, an approach with in situ measurements and physically based modelling is suggested. [less ▲]

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See detailImpact of thresholding techniques on X-ray soil microtomogram analyses
Beckers, Eléonore ULg; Léonard, Angélique ULg; Beekkerk van Ruth, Jöran ULg et al

in Geophysical Research Abstracts (2011), 13

Using X-ray microtomography, 3D soil structure can be visualised and analysed through useful factors like pore size distribution, shape, connectivity, orientation, etc. X-ray scans yield grey-level 2D ... [more ▼]

Using X-ray microtomography, 3D soil structure can be visualised and analysed through useful factors like pore size distribution, shape, connectivity, orientation, etc. X-ray scans yield grey-level 2D images, which can be recombined to form 3D structures. Treatments of the grey-level images can consist of either a binarization -distinguishing soil and pores- or a permeability level attribution directly linked to the grey-level values. The latter leads to problems in order to assign a permeability for each point (in soil a same grey level value can be assigned to points with a different permeability), as well as to analyse the 3D structure. On the other hand, treatment of black and white 3D structures is well-handled. However, the impact of the choice of one thresholding technique on the resulting images has already been demonstrated. Moreover, thresholding methods are various and numerous. Many of them are based on the image histogram analysis. But because of the soil complexity, the relevance of these techniques becomes debatable, with a risk of producing non reliable images. We propose to palliate this with a simple new algorithm based on physical measurements: it uses a loop fixing the threshold value in order to match the measured porosity for each sample. In this communication, our point is to highlight the impact of different thresholding techniques on the analysis and interpretation of our soil microtomograms. The underlying questions could be: Does the thresholding method influence our conclusions? Are the results depending on the sample itself or on the methodology? In order to answer these questions we tested the Otsu technique and our physically based algorithm. Soils samples were removed from the upper layer (Ap horizon) of a silty soil (Gentinnes, Brabant Walloon, Belgium) in plots with different management practices. In fact, since 2004, the field has been cultivated in conventional tillage (CT) or reduced tillage (RT). In order to empty the meso- and macroporosity, samples were placed under a 1.5 MPa pressure (Richards apparatus). Samples were then scanned by X-ray microtomography using a Skyscan-1172 high-resolution desktop micro-CT system (Skyscan, Kontich, Belgium). The cone beam source operated at 100 kV, using an aluminium filter. The detector configuration, i.e. 1048x2000 pixels with a 16-bit X-ray camera, and the distance source-object-camera were adjusted to produce images with a pixel size of 17 µm. Porosity was measured for each scanned sample. Then the threshold methods -the Otsu technique on one hand and our developed algorithm on the other - were applied, and morphological factors were calculated for both methods. A comparison of the first results shows a threshold influence on average porosity and number of pores, but also on connectivity factors and size distribution. The apparent porosity of the images, as well as connectivity, is underestimated with the Otsu technique. Despite the fact that the changes induced by thresholding are more important for RT than CT, global conclusions about the comparison of these agricultural practices are approximately the same in this case. However, differences between tillage systems are less important with the Otsu method, confirming the impact of choosing the adapted threshold method. [less ▲]

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See detailErosion and rainfall erosivity under climate change: rainfall simulation and soil losses measurement at field scale
Kummert, Nora ULg; Beckers, Eléonore ULg; Degre, Aurore ULg

in Geophysical Research Abstracts (2011), 13

Soil and water conservation is a big issue of this century. The soil is a non renewable resource. As we know, the change in climate brings more short erosive rainfall with a high capacity to take away the ... [more ▼]

Soil and water conservation is a big issue of this century. The soil is a non renewable resource. As we know, the change in climate brings more short erosive rainfall with a high capacity to take away the topsoil. Moreover, topsoil contains all the nutrients the plants needs. It is now essential that we found a new balance between productivity and durability. Impacts of new agricultural techniques on soil structure are already studied in different countries (i.e. Beckers et al., 2010; Walh et al., 2004; Malone et al., 2003). But what are the impacts on erosion? That is a question with few answers. And this is where our experiment comes, in order to link erosion and future erosion with management practices. Two ways exist to act against soil losses: enhancing soil structure or increasing vegetation cover. Our study aims at measuring soil losses and runoff under different practices and for a future scenario of climate change. This study explores new practices and measures their effects on erosion and runoff under a future rainfall. We focus on two cultures: sugar beet and maize. Each is tested under three different systems. For sugar beet soil structure impact is monitored: three tillage systems are tested: winter ploughing, fall ploughing and fall topsoiling. For maize vegetation cover impact is monitored: three seeding systems are studied: classical seeding (75 cm interrow), classical seeding with Ray-grass seeding in the interrows, and distributed seeding (obtained with a grains seeder). Rainfall simulation has been chosen for the study so the impacts of climate change can also be tested. A future rainfall was calculated based on a climate change scenario for Belgium (CCI-HYDR project, Willems, 2006-2010). A basic current rainfall of 100 years return period and 30 minutes duration (correspondent intensity: 70 mm/h) entered into the model gives the new rainfall. After the application of the scenario, the new rainfall has an intensity of 80 mm/h. This is our future rainfall used in this experiment. The simulations of this rainfall were carried on during the main crop season (between June and August). Three simulations were performed on sugar beet and two on maize on plots with the dimensions: 3 m length and 90 cm and 120 cm width respectively for sugar beet and maize (corresponding to two rows of the main culture). During each simulation soil losses and runoff quantities were measured. From the first year experiment, some tendencies can be observed. The topsoiling on sugar beet culture seems to produce less soil losses when the winter ploughing gives the lower quantities of runoff. The distributed seeding for the maize culture gives the lower rates for both soil losses and runoff quantities. Our experiment will be repeated at least for the next two years with new future rainfall to be tested. The climatic conditions are an important factor which can modify the behavior of soil response under rainfall event. More research has to be done in order to improve our knowledge of runoff and erosion phenomenon at smaller scale. [less ▲]

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See detailA methodology to assess the exactness of Stream Network modeling process on agricultural watersheds
Ouedraogo, Mohamar ULg; Degre, Aurore ULg; Beckers, Eléonore ULg et al

in Geophysical Research Abstracts (2011)

The goal of our study is to evaluate the exactness of stream network modeling process on agricultural watersheds. Agricultural watersheds topography is always changing, making it difficult to be modeled ... [more ▼]

The goal of our study is to evaluate the exactness of stream network modeling process on agricultural watersheds. Agricultural watersheds topography is always changing, making it difficult to be modeled. According to the standard ISO-7078 (ISO-7078, 1985) of the Inernational Organization of Standardization, the exactness of a measurement process or a modeled process can be defined as the difference between results obtained from the measurement process and a reference accepted as the «true value». A small watershed of a dozen hectares size has been surveyed by terrestrial LiDAR (Light Detecting And Ranging) scanner and photogrammetrical techniques to produce a row data of 30 cm resolution. Three interpolation techniques i.e. natural neighbourg, multiquadratic radial basis function and inverse distance weighted have been applied on the original data to create original digital elevation models (DEM) of 1 m resolution. RTK (Real Time Kinematics) GPS (Global Positionning System) ground control points have been surveyed on the watershed to evaluate DEM errors and fit a variogram that is used by a conditional sequencial gaussian simulation model to generate error maps. However, ground control point’s elevations accuracy is depending on the microtopography of parcels in an agricultural watershed. Depending on the crop that is planned by the farmer, the soil tillage will be different, and soil structure and roughness can considerably influence ground control point’s elevation. Analysis of variance and geostatistical methods have been applied on total station and RTK GPS data to estimate intervals in which, ground control points elevations vary. These intervals have been estimated for two parcels that soils are tilled in different ways. These errors are added to the generated errors maps to create final error maps. The final errors maps are added to the original DEM to create likely DEM realizations for the watershed (Temme and al., 2007). Then, two spurious sinks filtering methods (Colson 2006; Lindsay and Creed, 2005) and one flat area treatment method (Jenson and Domingue, 1988) are applied on each DEM realization for preprocessing. Finally, the three common flow direction extraction methods (D8, D-infity and Multiple Flow Direction) are applied on each preprocessed DEM to extract stream Network. The extracted stream network is overlapped with RTK GPS field positioned stream network i.e. a polyline format data. To estimate the exactness of the stream extraction methods, the polyline format is converted in raster format. That allows to compute for each pixel of the observed stream network, the distance to the extracted stream network. Then, for each pixel the mean distance can be calculated, and can be represented through the stream network. LiDAR technology is becoming useful for environment modeling because of his accuracy. Such quantity of data is not free of errors. This research will allow us to estimate the uncertainty of stream network modeled from agricultural watersheds by considering the main sources of errors that are propagated through computing processes. [less ▲]

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See detailL’hydrologie, une partenaire de la géomorphopédologie pour une gestion transéchelle des grands enjeux environnementaux
Degre, Aurore ULg; Sohier, Catherine ULg; Colard, François ULg et al

Conference (2010, November 24)

La zone insaturée du sol et du sous-sol est souvent qualifiée de zone critique, étant donné son rôle d’interfaçage entre les compartiments aérien et souterrain de notre environnement. Dans les thématiques ... [more ▼]

La zone insaturée du sol et du sous-sol est souvent qualifiée de zone critique, étant donné son rôle d’interfaçage entre les compartiments aérien et souterrain de notre environnement. Dans les thématiques du transfert des solutés ou de la conservation des eaux et des sols, les recherches d’hydrologie et d’hydraulique agricole s’appuient sur les informations pédologiques et ce depuis une échelle extrêmement locale jusqu’à la vision régionale de la gestion environnementale. Le rôle des descriptions pédologiques dans la gestion et la protection des ressources naturelles est donc majeur. La dérivation des paramètres hydrodynamiques depuis les descriptions pédologiques des sols permet à l’hydrologue de quantifier et de représenter spatialement la dynamique des échanges eau-sol-végétation-atmosphère, les déplacements de l’eau dans le sol et la vadose ainsi que les déplacements et les transformations des solutés. L’hydrologue en retire des indicateurs de pression sur les ressources hydriques de surface et souterraine. Il calcule des flux d’eau, de nutriments et de sédiments à un pas de temps très fin et durant de longues périodes (plus de 30 années). Les recherches présentées ici couvrent la modélisation hydrologique physiquement basée à l’échelle régionale qui vise l’analyse prospective (au-delà de 2020) des mesures envisagées pour limiter les pollutions diffuses d’origine agricole, tout comme des modélisations physiques détaillées en sites expérimentaux. L’érosion hydrique des sols est un autre un enjeu majeur de gestion environnementale. Le sol étant une ressource peu renouvelable, les techniques de conservation des sols et l’aménagement hydraulique des bassins versants ruraux nécessitent la plus grande considération. Elles sont un outil supplémentaire de limitation des apports au cours d’eau (tant en termes de sédiments qu’en termes de nutriments). Là encore, les descriptions pédologiques permettent de cibler les sols les plus sensibles. De plus, les cartes des sols qui incluent une interprétation géomorphologique permettent de confronter les modèles d’arrachement, de transport et de dépôt de sédiments aux observations des pédologues faites lors des premiers levés et actuellement en cours. Ces observations de terrain, réalisées à plusieurs dizaines d’années d’intervalle, constituent un gisement de données précieux et quasiment unique pour la validation des modèles hydrologiques de perte en sol et de dépôt et en vue de l’étude morphodynamique des bassins versants. Il reste actuellement des besoins en termes de description pédologique. Ils ont trait à la caractérisation plus fine de certains sigles, où l’introduction d’éléments relatifs à la dynamique des flux pourrait s’avérer pertinente. Toutefois, on peut constater que dans le contexte actuel et crucial de préservation des ressources eau et sol, l’hydrologie et la science du sol sont réaffirmées comme des partenaires forts de gestion des grands enjeux environnementaux. [less ▲]

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See detailEvolution des structures de sols sous itinéraires techniques contrastés : relations entre courbes de rétention et analyse par microtomographie à rayons X
Beckers, Eléonore ULg; Roisin, Christian; Léonard, Angélique ULg et al

in Milieux Poreux et Transferts Hydriques (2010, November), 56

Tillage reduction seems to affect porosity distribution, orientation and connectivity. Soil samples were removed from plots under conventional tillage or reduced tillage. Their water retention curves were ... [more ▼]

Tillage reduction seems to affect porosity distribution, orientation and connectivity. Soil samples were removed from plots under conventional tillage or reduced tillage. Their water retention curves were measured, and the characterization of soils porosity was made using x-ray microtomography measurements. Results show differences in the meso as well as in the macroporosity. [less ▲]

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See detailEvolution des structures de sols sous itinéraires techniques contrastés : relation entre courbes de rétention et analyse par microtomographie aux rayons X
Beckers, Eléonore ULg; Roisin, Christian; Léonard, Angélique ULg et al

Poster (2010, November)

Tillage reduction seems to affect porosity distribution, orientation and connectivity. Soil samples were removed from plots under conventional tillage or reduced tillage. Their water retention curves were ... [more ▼]

Tillage reduction seems to affect porosity distribution, orientation and connectivity. Soil samples were removed from plots under conventional tillage or reduced tillage. Their water retention curves were measured, and the characterization of soils porosity was made using x-ray microtomography measurements. Results show differences in the meso as well as in the macroporosity. [less ▲]

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See detailCaractérisation du réseau poral pour des sols à états de structures différenciés
Beckers, Eléonore ULg

Speech (2010)

Cette présentation s'attache à montrer l'intérêt de la microtomographie comme outil de caractérisation du réseau poral et , par là, de permettre la comparaison de strucutres différenciées par l ... [more ▼]

Cette présentation s'attache à montrer l'intérêt de la microtomographie comme outil de caractérisation du réseau poral et , par là, de permettre la comparaison de strucutres différenciées par l'application d'itinéraires techniques contrastés. [less ▲]

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See detailComparison of agricultural soils' structure depending on tillage system using X-ray microtomography
Beckers, Eléonore ULg; Ly, Sarann ULg; Léonard, Angélique ULg et al

in Geophysical Research Abstracts (2010, May), 12

This study aims at characterizing agricultural soils’ structure depending on the tillage system: conventional tillage or conservational tillage. Tillage reduction is an increasing practice, but the micro ... [more ▼]

This study aims at characterizing agricultural soils’ structure depending on the tillage system: conventional tillage or conservational tillage. Tillage reduction is an increasing practice, but the micro-structural effects on soils and on their hydrodynamic parameters are still not well described. Recent research shows non-converging results. Our point is to highlight fundamental differences in structure through characterization of soils porosity’s parameters using X-ray microtomography measurements coupled to image analysis. This attempt is in line with a more integrated experiment of which the aim is to quantify the effects of tillage intensity on lateral flow production, and finally on global water balance. Parameters’ measurements consist in a combined approach, based on two different space-time scales of exploration: fundamental scale, with soil sampling campaign for microtomography analysis, and field scale, with continuous flow measurements (plots’ dimensions: 18*28 m). For their part, parameters for water balance determination (precipitation, evapotranspiration…) are monitored on the field. All of these measurements have the main objective of hydrological modeling enhancement by taking into account a better lateral flow description. Discussion in this paper will focus on the first results obtained by X-ray microtomography measurements. Our experiment takes place in Gentinnes (Walloon Brabant, Belgium), on a field organized in a split-plot scheme. Since 2004, plots have been cultivated in conventional tillage or in reduced tillage. The latter consists in sowing after stubble ploughing of about 10cm. The crop rotation is sugar beet followed by winter wheat. The soil is mainly composed of silt loam. Soils samples, with a 3 cm diameter and a 5 cm height, were removed from the upper layer (Ap horizon) for both management practices. Samples are scanned by X-ray microtomography using a Skyscan-1172 high-resolution desk-top micro-CT system (Skyscan, Kontich, Belgium). The cone beam source operated at 100 kV, using an aluminium filter. The detector configuration, i.e. 1048×2000 pixels 16-bit X-ray camera, and the distance source-object-camera were adjusted to produce images with a pixel size of 17 µm. This resolution allows us to visualize both meso- and macro- porosity. In this study, half the samples were placed under a 15000 kPa pressure (corresponding pressure for the wilting point) in Richards’ apparatus in order to empty the meso- and macro-porosity. To determine a priori the class of porosity for the samples, relations between water retention and pressure head can be plotted using this apparatus. Scanning results consist in 2D images. The 2D images are recombined to form 3D structure. Then the pore network can be analyzed through useful factors like size distribution, shape, connectivity, orientation, tortuosity etc. [less ▲]

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See detailAssessing structure potential in soil and water conservation: monitoring top soil hydrology from micro to field scale.
Kummert, Nora ULg; Beckers, Eléonore ULg; Roisin, Christian et al

in Wollesen de Jonge, Lis; Moldrup, Per; Lindblad Vendelboe, Anders (Eds.) 1st international conference and exploratory workshop on soil architecture and physico-chemical functions "CESAR" (2010)

Soil structure is a key parameter influencing erosion and water transfers. This paper describes an experiment that covers different aspects of soil structure. Three tillage systems are tested: reduced ... [more ▼]

Soil structure is a key parameter influencing erosion and water transfers. This paper describes an experiment that covers different aspects of soil structure. Three tillage systems are tested: reduced tillage, and two ploughing systems. At micro-scale, analyses are tomography which study images to determine porosity characteristics (connectivity, size, number…) and pF curves where total available water and effective porosity are deducted. At field scale, soil losses and runoff are collected and measured after rainfall simulation on plots for the different tillage systems. The comparison of the results for both scales shows the links between phenomenons at those scales. [less ▲]

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See detailMesure et spatialisation des précipitations
Degre, Aurore ULg; Hirtt, Laura ULg; Beckers, Eléonore ULg

Learning material (2010)

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