References of "Roisin, Christian"
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See detail50 Years of contrasted residue management in an agricultural crop: Impacts on the soil carbon budget and on soil heterotrophic respiration.
Buysse, Pauline ULg; Roisin, Christian; Aubinet, Marc ULg

Conference (2012, February 08)

Within the context of Climate Change, crop management exerts a strong influence on the soil carbon (C) balance. This study aims (1) to estimate the C loss by soil heterotrophic respiration (SHR) in ... [more ▼]

Within the context of Climate Change, crop management exerts a strong influence on the soil carbon (C) balance. This study aims (1) to estimate the C loss by soil heterotrophic respiration (SHR) in different residue management treatments through the establishment of their soil C budgets and (2) to compare these estimations with field SHR measurements. Three contrasted treatments were considered: Residue Export (RE), Farm Yard Manure addition (FYM) and Residue Restitution after harvest (RR). They were established in 1959 and continuously applied since then at an experimental field located in the Hesbaye region in Belgium. The soil C budget was calculated for each treatment on the basis of total soil organic C content measurements and C input data compiled since the beginning of the experiment. This allowed estimating the C loss by SHR in the different treatments. SHR measurements were performed in 2010 and 2011 to compare them with the budget-based estimations and to assess SHR sensitivity to temperature in the different treatments. The soil C budgets showed that the soil under the RR treatment was likely to undergo the largest C loss by SHR since the beginning of the experiment. The comparison between the results from the C budget and the SHR field measurements, performed 50 years after the experiment had begun, did however show that the treatment that received the largest amount of crop residues (RR) did not necessarily sequestrate the most C or produce the largest CO2 fluxes (FYM). Besides, no significant difference between treatments was observed in the field measurements in terms of SHR sensitivity to temperature. Laboratory investigations (microbial biomass, basal respiration, metabolic diversity and soil fractionation) will later be performed to better understand the effects of long-term residue management on soil C dynamics. [less ▲]

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See detail1. Implantation des cultures
Bodson, Bernard ULg; Roisin, Christian; Vancutsem, Françoise ULg et al

in Livre Blanc - Céréales - Gembloux (2012, February 06)

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See detail1. Implantation des cultures
Bodson, Bernard ULg; Roisin, Christian; Vancutsem, Françoise ULg et al

in Livre Blanc - Céréales-Gembloux - Informations avant les semis (2011, September 08)

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See detailEffects of long term soil organic matter restitution mode on soil heterotrophic respiration and soil biological properties.
Buysse, Pauline ULg; Carnol, Monique ULg; Malchair, Sandrine ULg et al

Poster (2011, July)

Soil heterotrophic respiration (SHR) is the process by which CO2 is released during organic matter decomposition. It is generally expected that SHR can act as a positive feedback to global warming ... [more ▼]

Soil heterotrophic respiration (SHR) is the process by which CO2 is released during organic matter decomposition. It is generally expected that SHR can act as a positive feedback to global warming, therefore leading to more CO2 release into the atmosphere. It is thus important to better understand this process. Particularly, agricultural soils may behave as important CO2 sources that are strongly influenced by soil and crop management (e.g. organic matter restitution modes, hereafter “OM-RM”). The present study aimed at determining if, after more than 50 years of application of different OM-RM, (1) significant differences of SHR fluxes can be observed between treatments, (2) SHR responses to temperature and soil moisture content can be affected by the OM-RM and (3) the experimental design is suitable to assess potential differences between treatments. The experimental field is situated in Liroux, near Gembloux in Belgium. At that site, a long term experiment with different OM-RM runs from 1959 onwards. For the present study, three contrasted treatments were considered: (1) exportation of all residues after harvest, (2) addition of manure once every three to four years and (3) restitution of residues after harvest. SHR flux measurements were carried out manually on fourteen occasions from 2 April to 30 July 2010, using a dynamic closed chamber system. Temperature and soil moisture content at 5 cm depth were also measured manually. Results showed that after more than 50 years of OM-RM application, no significant differences could be observed between the three treatments in terms of SHR fluxes and SHR responses to temperature or soil moisture, while the soil organic carbon content did vary significantly between them. The sensitivity to temperature was quite low in all treatments, with a mean Q10 value of 1,36. Besides, SHR fluxes were seen to be more responsive to increases in soil water content than to absolute soil moisture content values. Indeed, when soil moisture content increased between two consecutive measurement dates, the ratio of the corresponding SHR fluxes was larger than 1. Particularly dry conditions in 2010 may actually have caused the fluxes to be very low, making the assessment of differences between treatments more difficult. Moreover, soil dryness is likely to be responsible for the SHR flux increases after rain events, as caused by re-solubilization of organic compounds. Also, an important spatial variability was observed, which may have obscured the assessment of potential differences between treatments. Further investigations will consist in performing a new flux measurement campaign in 2011 that will take the spatial variability issue into account, and in monitoring microbial and soil properties in the different treatments, such as microbial biomass, metabolic activity and labile carbon. [less ▲]

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See detailEffects of long term soil organic matter restitution mode on soil heterotrophic respiration and soil biological properties.
Buysse, Pauline ULg; Carnol, Monique ULg; Malchair, Sandrine ULg et al

Conference (2011, May 12)

For more than 50 years, an agricultural site divided in several plots is submitted to different organic matter restitution mode to the soil (crop residues, manure,...). The objectives of this study were ... [more ▼]

For more than 50 years, an agricultural site divided in several plots is submitted to different organic matter restitution mode to the soil (crop residues, manure,...). The objectives of this study were to determine (1) whether these different treatments may cause differences between treatments in terms of soil heterotrophic respiration, that would be of the same order of magnitude than differences in total soil organic carbon, (2) how temperature and soil moisture content affect soil heterotrophic respiration in the different treatments, and (3) how different soil biological properties (microbial biomass, metabolic diversity, labile carbon content) are affected in the different treatments. The results from a first measurement campaign carried out in 2010 are presented, together with the remaining questions at this stage of the study. [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 detail4. La fumure azotée
Vancutsem, Françoise ULg; Seutin, Benoit ULg; Destain, Jean-Pierre ULg et al

in Livre Blanc: Céréales - Gembloux (2011, February 23)

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See detail2. Implantation des cultures
Bodson, Bernard ULg; Roisin, Christian; Vancutsem, Françoise ULg et al

in Livre Blanc: Céréales - Gembloux (2011, February 23)

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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 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 detailImplantation des cultures
Bodson, Bernard ULg; Roisin, Christian; Vancutsem, Françoise ULg et al

in Livre Blanc: Céréales - Gembloux - Informations avant les semis (2010, September 09)

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See detailLa fumure azotée
Destain, Jean-Pierre ULg; Roisin, Christian; Marcoen, Jean Marie ULg et al

in Livre Blanc: Céréales - Gembloux (2010, February 24)

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See detailImplantation des cultures
Bodson, Bernard ULg; Roisin, Christian; Vancutsem, Françoise ULg et al

in Livre Blanc: Céréales - Gembloux (2010, February 24)

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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 detailImplantation des cultures
Bodson, Bernard ULg; Roisin, Christian; Vancutsem, Françoise ULg et al

in Livre Blanc: Céréales - Gembloux - Informations avant les semis (2009, September 10)

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See detailImplantation des cultures
Bodson, Bernard ULg; Roisin, Christian; Vancutsem, Françoise ULg et al

in Livre Blanc: Céréales - Gembloux (2009, February 18)

Expérimentations, résultats, perspectives, recommandations pratiques (date de semis, préparation du sol, profondeur de semis, densité de semis, protection des semis)

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See detailImplantation des cultures
Bodson, Bernard ULg; Roisin, Christian; Vancutsem, Françoise ULg et al

Conference given outside the academic context (2008)

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See detailImplantation des cultures
Bodson, Bernard ULg; Roisin, Christian; Vancutsem, Françoise ULg et al

in Livre Blanc: Céréales - Gembloux (2008, February 20)

Detailed reference viewed: 2 (0 ULg)