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See detailÉVOLUTION DE LA TENEUR EN EAU LE LONG D’UNE TOPOSEQUENCE FORESTIERE ARGILO-LIMONEUSE
Deraedt, Deborah ULg; Colinet, Gilles ULg; Degré, Aurore ULg

in Milieux Poreux et Transferts Hydriques (in press)

For the hydrological modeling of forested watersheds, the understanding of the forest hydrodynamic is essential. This study focusses on the hydrology of a Belgian forested plot with high stoniness and ... [more ▼]

For the hydrological modeling of forested watersheds, the understanding of the forest hydrodynamic is essential. This study focusses on the hydrology of a Belgian forested plot with high stoniness and steep slope. The soil water content is monitored at several positions on the toposequence and at different depth. During rain events, peak in soil water content are observed in different depth depending on the position along the toposequence. [less ▲]

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See detailNo favorable effect of reduced tillage on microbial communities in a silty loam soil (Belgium)
Degrune, Florine ULg; Theodorakopoulos, Nicolas ULg; Dufrêne, Marc ULg et al

Poster (2015, December 01)

To date, only a few studies have applied metagenomics to investigate the influence of different tillage regimes and types of crop residue management on soil microbial communities. These studies were ... [more ▼]

To date, only a few studies have applied metagenomics to investigate the influence of different tillage regimes and types of crop residue management on soil microbial communities. These studies were conducted under specific climates on soils characterized by particular land-use histories. A very different ecological context is to be found in certain areas of Western Europe, such as central Belgium, whose loess-derived soils are among the most fertile in the world and have long been used for intensive agriculture. Specific objectives were to determine diversity levels and changes in microbial community composition under different combinations of tillage regime (conventional vs. reduced) and crop residue fate (residue removal R- vs. residues left R+ on the field). As reduced tillage results in two contrasting zones (the first centimeters of soil are mixed each year, while the soil below remains unperturbed), we chose to perform the analysis at two depths: 0 to 5 cm and 15 to 20 cm. [less ▲]

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See detailEvaluation of phosphorus bioavailability according to the soil organic matter content
Barbieux, Sophie ULg; Colinet, Gilles ULg

Poster (2015, July)

Phosphorus (P) is an essential nutrient for plants. The organic matter contains significant amounts of P which can be mineralized and supply soil solution. We hypothesize that increasing P organic pools ... [more ▼]

Phosphorus (P) is an essential nutrient for plants. The organic matter contains significant amounts of P which can be mineralized and supply soil solution. We hypothesize that increasing P organic pools in soils is a way to improve its progressive release for plants and alleviate risks of immobilization in mineral forms. The main objective of this study is to evaluate the P bioavailability and its uptake by plants according to the soil organic matter (SOM) content. The experimental protocol is based on a micro-culture in pots. The test-plant used is ryegrass (Lolium perenne L.). Eight silty soils were selected from vegetable gardens (5) and from a long-term fertilization trial on field (3). They present a gradient of SOM (from 2 to 9 %) and available P content (from 5 to 55 mg/100g). Plants were first grown in pure sand and P-free Hoagland nutritive solution. Ten days after plant emergence, roots were brought into contact with the studied soil during about one month. The experiment was stopped after three harvests (every 10 days) and three growth cycles. At the end of the experimentation, analyses were performed on plant material (biomass, P content) and on soil (soluble P, available P, microbial P, pH, phosphatase activity, hot water carbon, nitrate). Besides this study, an incubation experiment was carried out with the same soils without plant to assess soil P status at each harvest time. Paper will present the main findings of the experiment. Especially, the following issues should find answers: (1) do higher levels of SOM and organic phosphorus modify the evolution of P content in soil solution and its uptake by plants?, (2) are the biological processes involved in P cycling promoted in soils with higher SOM content? [less ▲]

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See detailDetermination of Zinc, Cadmium and Lead Bioavailability in Contaminated Soils at the Single-Cell Level by a Combination of Whole-Cell Biosensors and Flow Cytometry
Hurdebise, Quentin ULg; Tarayre, Cédric ULg; Fischer, Christophe ULg et al

in Sensors (2015)

Zinc, lead and cadmium are metallic trace elements (MTEs) that are widespread in the environment and tend to accumulate in soils because of their low mobility and non-degradability. The purpose of this ... [more ▼]

Zinc, lead and cadmium are metallic trace elements (MTEs) that are widespread in the environment and tend to accumulate in soils because of their low mobility and non-degradability. The purpose of this work is to evaluate the applicability of biosensors as tools able to provide data about the bioavailability of such MTEs in contaminated soils. Here, we tested the genetically-engineered strain Escherichia coli pPZntAgfp as a biosensor applicable to the detection of zinc, lead and cadmium by the biosynthesis of green fluorescent protein (GFP) accumulating inside the cells. Flow cytometry was used to investigate the fluorescence induced by the MTEs. A curvilinear response to zinc between 0 and 25 mg/L and another curvilinear response to cadmium between 0 and 1.5 mg/L were highlighted in liquid media, while lead did not produce exploitable results. The response relating to a Zn2+/Cd2+ ratio of 10 was further investigated. In these conditions, E. coli pPZntAgfp responded to cadmium only. Several contaminated soils with a Zn2+/Cd2+ ratio of 10 were analyzed with the biosensor, and the metallic concentrations were also measured by atomic absorption spectroscopy. Our results showed that E. coli pPZntAgfp could be used as a monitoring tool for contaminated soils being processed. [less ▲]

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See detailEvaluation of soil structural changes through macroscopic and microscopic measurement
Parvin, Nargish ULg; Degré, Aurore ULg; Chelin, Marie ULg et al

Poster (2015, April 16)

The heterogeneity of soil structure and pore size distribution are highly influenced by external factors like tillage systems and other agricultural management practices. However, changes in soil ... [more ▼]

The heterogeneity of soil structure and pore size distribution are highly influenced by external factors like tillage systems and other agricultural management practices. However, changes in soil hydrodynamic behavior are not fully understood and are still under research. Also, researchers have explained the impact of tillage practices on soil hydraulic properties related to pore size distribution, connectivity and orientation are involved but the characterization of these modifications and consequences remains a challenge. Furthermore, the relation between macroscopic measurements and microscopic investigation of the soil structure remains scarce. Recently, X-ray tomography (X- μCT) has been used in order to characterize changes in soil pore size distribution in various contexts and the method is able to link microtomography information to hydrodynamic measurement. In our study, X-μCT has been used in order to characterize changes in soil pore system. Since, tomography does not count most of the micropores, Richards’ pressure plate and evaporation method was also combined to get complete range of pore size distribution. We found good match between evaporation data with X-μCT at the macropore scale and evaporation data with pressure plate method at micropore scale. X-μCT data refines retention and hydraulic curves near saturation where Richards’ data alone can lead to numerous sets of fitted parameters. On the otherhand, evaporation data (Hyprop apparatus ©) provide comparable datasets with X-μCT. Combining micro and macroscopic measurements allows us to validate X-μCT information, which is otherwise not so obvious. [less ▲]

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See detailInvestigating the Effects of Plant Root Exudates on PAHs Bioavailability to Soil Microorganisms in Contaminated Brownfields : Research Methodology.
Davin, Marie ULg; Lognay, Georges ULg; Fauconnier, Marie-Laure ULg et al

Poster (2015, January 30)

As a result of heavy industrial past activities, an estimated 6,000 brownfields require remediation in Wallonia. This number rises to over 3.5 million in Europe. Polycyclic Aromatic Hydrocarbons (PAHs ... [more ▼]

As a result of heavy industrial past activities, an estimated 6,000 brownfields require remediation in Wallonia. This number rises to over 3.5 million in Europe. Polycyclic Aromatic Hydrocarbons (PAHs) represent 17% of treated pollutants in Wallonia (Aldric et al., 2011). Current remediation techniques are rather expensive and technically demanding (Megharaj et al., 2011). Based on the observation that PAHs soil content decreases in the presence of plants (Cheema et al., 2010), the PhD aims at developing alternative PAHs remediation techniques in brownfields. It is articulated around three research axes. The first axis focusses on plant exudates and how they may improve PAHs bioavailability to soil microorganisms and enhance their degradation. This will be investigated by (i) characterizing several contaminated soils (physico-chemical parameters) and PAH content and factors of bioavailability, (ii) selecting a plant model and collecting root exudates, and (iii) evaluating the effects of exudates on PAHs bioavailability. The objective of the second axis is to evaluate the effects of plant exudates on PAHs degrading microorganisms by (i) comparing PAHs biodegradation in the presence/absence of exudates and (ii) assessing the potential toxic effects of exudate compounds on the microbial communities. The aim of the third axis is to study plant-pollutants interactions by (i) establishing the plant tolerance to several contamination levels and (ii) following PAHs bioavailability when facing real exudation rates, on the field. [less ▲]

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See detailA novel sub-phylum method discriminates better the impact of crop management on soil microbial community
Degrune, Florine ULg; Dufrêne, Marc ULg; Colinet, Gilles ULg et al

in Agronomy for Sustainable Development (2015)

Soil microorganisms such as mycorrhizae and plant-growth-promoting rhizobacteria have beneficial effects on crop productivity. Agricultural practices are known to impact soil microbial communities, but ... [more ▼]

Soil microorganisms such as mycorrhizae and plant-growth-promoting rhizobacteria have beneficial effects on crop productivity. Agricultural practices are known to impact soil microbial communities, but past studies examining this impact have focused mostly on one or two taxonomic levels, such as phylum and class, thus missing potentially relevant information from lower levels. Therefore we propose here an original, sub-phylum method for studying how agricultural practices modify microbial communities. This method involves exploiting the available sequence information at the lowest taxonomic level attainable for each operational taxonomic unit. In order to validate this novel method we assessed microbial community composition using 454 pyrosequencing of 16S and 28S rRNA genes, then we compared the results with results of a phylum-level analysis. Agricultural practices included conventional tillage, reduced tillage, residue removal and residue retention. Results show that, at the lowest taxonomic level attainable, tillage is the main factor influencing both bacterial community composition, accounting for 13% of the variation, and fungal community composition, accounting for 18% of the variation. Whereas phylum-level analysis failed to reveal any effect of soil practice on bacterial community composition, and missed the fact that different members of the same phylum responded differently to tillage practice. For instance, the fungal phylum Chytridiomycota showed no impact of soil treatment, while sub-phylum-level analysis revealed an impact of tillage practice on the Chytridiomycota sub-groups Gibberella, which includes a notorious wheat pathogen, and Trichocomaceae. This clearly demonstrates the necessity of exploiting the information obtainable at sub-phylum level when assessing the effects of agricultural practice on microbial communities. [less ▲]

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See detailDegree of phosphorus saturation in agricultural loamy soils with a near-neutral pH
Renneson, Malorie ULg; Vandenberghe, Christophe ULg; Dufey, Joseph et al

in European Journal of Soil Science (2015), 66

The degree of phosphorus saturation (DPS) represents the ratio of sorbed phosphorus (P) to the P sorption capacity (PSC) of soils. In some countries, DPS is used to evaluate the risk of P loss and surface ... [more ▼]

The degree of phosphorus saturation (DPS) represents the ratio of sorbed phosphorus (P) to the P sorption capacity (PSC) of soils. In some countries, DPS is used to evaluate the risk of P loss and surface water eutrophication. This study investigated DPS measurement and prediction in neutral loamy soils fromWallonia, Belgium. A total of 57 agricultural topsoil samples subject to diverse P management were evaluated. No satisfactory relationship could be found between PSC determined by a one-point short-term isotherm in the laboratory and the sum of aluminium and iron extracted by oxalate (Alox +Feox). The equation PSC=a Alox +b pHw appeared to be more appropriate for estimating PSC in the soils studied. These soils had a near-neutral pH, and P fixation processes linked to the presence of calcium ions or carbonates were important. Comparisons of DPS with soil-test P and water-extracted P suggested that DPS could be a useful agronomic and/or environmental indicator. Our results also showed that DPS values between 20 and 30% corresponded to the agronomic optimum of soil P content. Consequently, DPS may be used as an indicator of P status in neutral soils, provided that the PSC assessment is adapted to the local soil characteristics. [less ▲]

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See detailAssessment of soil metal distribution and environmental impact of mining in Katanga (Democratic Republic of Congo)
Pourret, Olivier; Lange, Bastien; Bonhoure, Jessica et al

in Applied Geochemistry (2015)

Metal and metalloid (As, Cd, Co, Cu, Pb and Zn) distribution in soils from the Katanga Copperbelt (Democratic Republic of Congo) is investigated in order to characterize the environmental impacts of ... [more ▼]

Metal and metalloid (As, Cd, Co, Cu, Pb and Zn) distribution in soils from the Katanga Copperbelt (Democratic Republic of Congo) is investigated in order to characterize the environmental impacts of mining and smelting activities in that area. The concentrations of Cu, Co, As, Zn, Pb and Cd in soils from mining sites are higher than in non-metalliferous sites and above permissible metal and metalloid concentrations in soils. Moreover, the fractionation and mobility of Co, and Cu in such environment is assessed using the application of both ammonium acetate-EDTA extraction and speciation modeling (WHAM 6). The resulting data set covers wide range of environmental conditions (pH, trace metals concentration, natural soils and soils affected by mining and ore processing). These extractions show that only a small fraction of Cu and Co is mobile, with variation depending on sites: mobility is higher in soils affected by mining and ore processing. The strong affinity of Mn-oxides for Co may explain lower Co mobility in Mn-rich soils. The high Mn and Fe contents of Cu-Co soils from Katanga may actually exert a protective effect against the toxic effects of Co. Finally, Cu-Co speciation modeling of contaminated sites emphasizes that organic matter strongly sorb Cu whereas Co speciation is mostly by Mn content. This type of study leads to a better understanding of metal fractionation and can guide to define different practices of phytoremediation. © 2015 Elsevier Ltd. [less ▲]

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See detailCaractérisation des systèmes sols-plantes dans les collines de l’arc cuprifère du Katanga (synthèse bibliographique)
Kaya Muyumba, Donato; Liénard, Amandine ULg; Mahy, Grégory ULg et al

in Biotechnologie, Agronomie, Société et Environnement = Biotechnology, Agronomy, Society and Environment [=BASE] (2015), 19(2), 204-214

Introduction: The Copper belt of Katanga presents huge resources of Cu and Co-ore. On the copper hills, mineralized rocks outcrop and a specific flora did develop as a response to the high levels of Cu ... [more ▼]

Introduction: The Copper belt of Katanga presents huge resources of Cu and Co-ore. On the copper hills, mineralized rocks outcrop and a specific flora did develop as a response to the high levels of Cu and Co in soil. Soil-vegetation relationships need to be understood in order to elaborate biodiversity conservation programs prior to industrial mining of the copper hills. Literature: This paper reviews knowledge about soil characterization in the copper hills of Katanga and makes proposals for further research about the influence of the very specific chemical conditions of contaminated soils on the vegetation. The focus was put on the geochemical background and the bioavailability of Cu and Co. A lot of progress has been made recently about identification of soil-vegetation relationships. Conclusion: However, the issue of Cu and Co mobility within soil-plant systems is not entirely solved. [less ▲]

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See detailImpact of stone content on soil moisture measurement with capacitive sensors 10HS (Decagon)
Deraedt, Deborah ULg; Bernard, Julien ULg; Biettlot, Louise ULg et al

in Geophysical Research Abstracts (2015), 17

Lot of soil survey focused on agricultural soils. For practical reasons, those soils have a low stone content. So, most of the soil water content sensors are placed on low stone content soils and the ... [more ▼]

Lot of soil survey focused on agricultural soils. For practical reasons, those soils have a low stone content. So, most of the soil water content sensors are placed on low stone content soils and the calibration equations are developed for them. Yet some researches take an interest in forest soils that are often much different from the previous ones. The differences lie in their stone content and their slope. Lots of studies have proved the importance of making soil specific calibration of the soil water content sensor. As our lab use regularly the 10HS sensors (Decagon Devices, United States) in forested soil, we decided to evaluate the importance of the stone content in the soil moisture measurement. The soil used for this experimentation comes from Gembloux (50◦33’54.9”N, 4◦42’11.3”E). It is silt that has been sieved at 2 mm to remove the gravel. The stones used to form the samples come from an experimental site located in the Belgian Ardennes (50◦1’52.6”N, 4◦53’22.5”E). They are mainly composed of schist with some quartz and sandstone elements. Initially, only five samples were constructed with three replications each. The size and the proportion of stones were the variables. Stones were classified in two groups, the first contains gravels whose size is less than 1,5 cm and a the second contains gravels whose size is comprised between 2 and 3 cm. The proportions of stone selected for the experiment are 0, 20 and 40%. In order to generate validation data, two more samples were constructed with intermediate proportion of stone content (30%). The samples were built in PVC container which dimensions are slightly bigger than the sensor volume of influence (1.1-1.3l). The soil samples were saturated and then dried on a thermal chamber set at about 32◦C. During at least 14 days, the samples soil water content was determined by the sensor measurement with the Procheck read-out system (Decagon Devices, United State) and by weighting the samples thrice a day. The evolution of the soil sample height was monitored as well. As first result, the stone content is a parameter that seems to influence soil water content. The stone size is no important. Because soil moisture deserves to be measured accurately in every soil and to confirm the first results the experiment is going on with more samples, different stone proportions, other sensor positioning and a natural air drying. [less ▲]

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See detailDiachronical soil surveys: a way to quantify long term diffuse erosion
Pineux, Nathalie ULg; Michel, Brieuc ULg; Legrain, Xavier ULg et al

in Geophysical Research Abstracts (2015), 17

The loess belt of Western Europe is a high-risk area regarding diffuse erosion. It is due to the climate and the topography but also to the soil type. Loamy soils are naturally highly sensitive to diffuse ... [more ▼]

The loess belt of Western Europe is a high-risk area regarding diffuse erosion. It is due to the climate and the topography but also to the soil type. Loamy soils are naturally highly sensitive to diffuse erosion. Hence, these soils are very fertile. So, they are intensively cultivated which increases their sensitivity to erosion. Sheet erosion is an erosion type strongly represented in these regions. Contrarily to the concentrated form of erosion which happens more brutally, sheet erosion needs long-term observation time-scales, which remains rare. In Belgium, a soil map was established in 1956. This map is quite detailed and notably informs about the different horizons which are in the profile (ploughed horizon, eluvial horizon, clay included between the horizons, carbonate-free loess horizon, and all these were characterised by drainage class) and their depth. It was based on a dense augering network across the country (one point every 75 meters). A new augering campaign was done again in 2014. It consisted in one observation every 50 meters on an agricultural watershed of 124 hectares located in the centre of Belgium. This catchment has been cultivated since the 14th century and is representative of the local context (gentle slope (3-8%), plot size (mean value of 10 ha), …). We compared the two soil maps produced on this site with a 58years time lapse. Results show that the large majority of the watershed falls from upslope soils with weak erosion to slope soils with strong erosion. The soil thickness diminished in some zones to 1m10 (minimum estimation) of erosion. This comparison shows that very few upslope soils are preserved. On the other hand, the areas where colluviums were present to the full depth stay at the same place in the main thalweg of the watershed. Other areas on the watershed seem to be subject to a (minimum estimation) of 40cm of sediments deposition. Large areas in the watershed suffered from erosion and came to deposition areas as the clay horizon is no longer observed under the colluviums. It can be highlighted that soil depths were worryingly lost during 58 years of tillage and that some soils were converted to colluviums which is of lower agronomical quality than the original soils which had a clay horizon below to keep water. Diachronical soil survey offers an unique insight of long term diffuse erosion and should demonstrate the importance of preserving soils even in regions where agricultural yields are not (yet) affected by erosion. [less ▲]

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See detailContact resistance problems applying ERT on low bulk density forested stony soils Is there a solution?
Deraedt, Deborah ULg; Touzé, Camille; Robert, Tanguy et al

in Geophysical Research Abstracts (2015), 17

Electrical resistivity tomography (ERT) has often been put forward as a promising tool to quantify soil water and solute fluxes in a non-invasive way. In our experiment, we wanted to determine ... [more ▼]

Electrical resistivity tomography (ERT) has often been put forward as a promising tool to quantify soil water and solute fluxes in a non-invasive way. In our experiment, we wanted to determine preferential flow processes along a forested hillslope using a saline tracer with ERT. The experiment was conducted in the Houille watershed, subcatchment of the Meuse located in the North of Belgian Ardennes (50˚1’52.6”N, 4˚53’22.5”E). The climate is continental but the soil under spruce (Picea abies (L.) Karst.) and Douglas fire stand (Pseudotsuga menziesii (Mirb.) Franco) remains quite dry (19% WVC in average) during the whole year. The soil is Cambisol and the parent rock is Devonian schist covered with variable thickness of silty loam soil. The soil density ranges from 1.13 to 1.87 g/cm3 on average. The stone content varies from 20 to 89% and the soil depth fluctuates between 70 and 130 cm. The ERT tests took place on June 1st 2012, April 1st, 2nd and 3rd 2014 and May 12th 2014. We used the Terrameter LS 12 channels (ABEM, Sweden) in 2012 test and the DAS-1 (Multi-Phase Technologies, United States) in 2014. Different electrode configurations and arrays were adopted for different dates (transect and grid arrays and Wenner – Schlumberger, Wenner alpha and dipole-dipole configurations). During all tests, we systematically faced technical problems, mainly related to bad electrode contact. The recorded data show values of contact resistance above 14873 Ω (our target value would be below 3000 Ω). Subsequently, we tried to improve the contact by predrilling the soil and pouring water in the electrode holes. The contact resistance improved to 14040 Ω as minimum. The same procedure with liquid mud was then tested to prevent quick percolation of the water from the electrode location. As a result, the lower contact resistance dropped to 11745 Ω. Finally, we applied about 25 litre of saline solution (CaCl2, 0.75g/L) homogeneously on the electrode grid. The minimum value of contact resistance reduced to 5222 Ω. This improved the contact resistance substantially, but complicates the execution of a pulse tracer experiment. To date we did not find any better solution to this problem and we keep searching a way to improve the contact resistance in stony forested soils with very low bulk density. We would like to exchange on these questions with EGU attendees in order to improve the experimental design or point out a new research path for these specific conditions. This could lead to enhance the use of ERT in soils with low density and high stone content. [less ▲]

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