2D characterization of near-surface V P/V S: surface-wave dispersion inversion versus refraction tomography

International audienceThe joint study of pressure (P-) and shear (S-) wave velocities (Vp and Vs ), as well as their ratio (Vp /Vs), has been used for many years at large scales but remains marginal in near-surface applications. For these applications, and are generally retrieved with seismic refraction tomography combining P and SH (shear-horizontal) waves, thus requiring two separate acquisitions. Surface-wave prospecting methods are proposed here as an alternative to SH-wave tomography in order to retrieve pseudo-2D Vs sections from typical P-wave shot gathers and assess the applicability of combined P-wave refraction tomography and surface-wave dispersion analysis to estimate Vp/Vs ratio. We carried out a simultaneous P- and surface-wave survey on a well-characterized granite-micaschists contact at Ploemeur hydrological observatory (France), supplemented with an SH-wave acquisition along the same line in order to compare Vs results obtained from SH-wave refraction tomography and surface-wave profiling. Travel-time tomography was performed with P- and SH- wave first arrivals observed along the line to retrieve Vtomo p and Vtomo s models. Windowing and stacking techniques were then used to extract evenly spaced dispersion data from P-wave shot gathers along the line. Successive 1D Monte Carlo inversions of these dispersion data were performed using fixed Vp values extracted from Vtomo p the model and no lateral constraints between two adjacent 1D inversions. The resulting 1D Vsw s models were then assembled to create a pseudo-2D Vsw s section, which appears to be correctly matching the general features observed on the section. If the pseudo-section is characterized by strong velocity incertainties in the deepest layers, it provides a more detailed description of the lateral variations in the shallow layers. Theoretical dispersion curves were also computed along the line with both and models. While the dispersion curves computed from models provide results consistent with the coherent maxima observed on dispersion images, dispersion curves computed from models are generally not fitting the observed propagation modes at low frequency. Surface-wave analysis could therefore improve models both in terms of reliability and ability to describe lateral variations. Finally, we were able to compute / sections from both and models. The two sections present similar features, but the section obtained from shows a higher lateral resolution and is consistent with the features observed on electrical resistivity tomography, thus validating our approach for retrieving Vp/Vs ratio from combined P-wave tomography and surface-wave profiling

Choisir les pneumatiques

[Departement_IRSTEA]EAA [TR1_IRSTEA]EAA7-MECAPLUS, Prestations d'ingénierie et d'essais de terrain pour les organismes interprofessionnels et les PME-PMIThis practical guide reviews the roles, description, choice criteria, use advices, comparison characteristics of agricultural pneumatics available on the market.Ce guide pratique présente : rôles, description, critères de choix, consignes d'utilisation, tableaux de comparaison des caractéristiques des pneumatiques agraires disponibles sur le marché

Consequences de la repartition des matieres organiques sur le comportement du sol

National audienc

Pietinement a la pature.

National audienc

Le rôle des lombrociens sur le fonctionnement des sols. Impacts des pratiques agricoles

*INRA Unité Sol et Agronomie Rennes (FRA) Diffusion du document : INRA Unité Sol et Agronomie Rennes (FRA)National audienc

Effets des jachères "nouvelle PAC" sur les composantes physiques et chimiques du milieu

*INRA, centre de Grignon Diffusion du document : INRA, centre de GrignonNational audienc

Effect of organic matter on soil inoculum potential and soil suppressiveness to <em>Gaeumannomyces graminis</em> var. <em>tritici</em> and <em>Rhizoctonia solani</em>

National audienceIt is widely recognized that organic amendments may reduce crop losses caused by soil borne plant pathogens. Most of the studies conducted so far were related to short term effects observed in vegetable cropping systems. The long term effects of compost or manure amendments in field cropping systems has been investigated in Australia and, concerning Rhizoctonia solani diseases on wheat, inconsistent results were reported. Two large field experiments were set up in 1996, at Le Rheu and la Jaillière (France), to study the effects of organic fertilization in wheat and maize production. In 2006, at the end of the experiments, soil was sampled to assess the effects of the organic matter fertilization on the soil inoculum potential and soil suppressiveness to diseases caused by Gaeumannomyces graminis var. tritici (Ggt, take all) and R. solani. Bioassays were set up in growth chamber, using wheat and carrots to measure soil inoculum potential and soil suppressiveness to Ggt and R. solani, respectively. A pathological index was used to evaluate the disease severity caused by Ggt on wheat and area under the disease progress curve (AUDPC) was calculated to quantify the disease severity caused by R. solani. ANOVA was used to compare the data. At both locations, the inoculum potential of the soils naturally infested by Ggt was low and similar in plots amended with different organic matters and mineral fertilization. The level of soil suppressiveness to take-all was high in plots amended with organic matter compared to the low level after mineral fertilisation. This suggests that organic amendments preserved the suppressive ability of the soil towards take all when a wheat/maize rotation is performed. Concerning R. solani, the soil inoculum potential was reduced in plots amended with organic matters, but only at La Jaillière not at Le Rheu. At both 2 locations, soil suppressiveness to R. solani damping-off was not affected by organic amendments. There were neither clear positive nor detrimental effects of organic fertilisation in a wheat/maize rotation. Therefore organic matter can be used to improve soil fertility without any negative effects on the phytosanitary status of soil

Effect of organic matter on soil inoculum potential and soil suppressiveness to Gaeumannomyces graminis var. tritici and Rhizoctonia solani

It is widely recognized that organic amendments may reduce crop losses caused by soil borne plant pathogens. Most of the studies conducted so far were related to short term effects observed in vegetable cropping systems. The long term effects of compost or manure amendments in field cropping systems has been investigated in Australia and, concerning Rhizoctonia solani diseases on wheat, inconsistent results were reported. Two large field experiments were set up in 1996, at Le Rheu and la Jaillière (France), to study the effects of organic fertilization in wheat and maize production. In 2006, at the end of the experiments, soil was sampled to assess the effects of the organic matter fertilization on the soil inoculum potential and soil suppressiveness to diseases caused by Gaeumannomyces graminis var. tritici (Ggt, take all) and R. solani. Bioassays were set up in growth chamber, using wheat and carrots to measure soil inoculum potential and soil suppressiveness to Ggt and R. solani, respectively. A pathological index was used to evaluate the disease severity caused by Ggt on wheat and area under the disease progress curve (AUDPC) was calculated to quantify the disease severity caused by R. solani. ANOVA was used to compare the data. At both locations, the inoculum potential of the soils naturally infested by Ggt was low and similar in plots amended with different organic matters and mineral fertilization. The level of soil suppressiveness to take-all was high in plots amended with organic matter compared to the low level after mineral fertilisation. This suggests that organic amendments preserved the suppressive ability of the soil towards take all when a wheat/maize rotation is performed. Concerning R. solani, the soil inoculum potential was reduced in plots amended with organic matters, but only at La Jaillière not at Le Rheu. At both 2 locations, soil suppressiveness to R. solani damping-off was not affected by organic amendments. There were neither clear positive nor detrimental effects of organic fertilisation in a wheat/maize rotation. Therefore organic matter can be used to improve soil fertility without any negative effects on the phytosanitary status of soil

Etude expérimentale statistique des structures cibles de la réaction de Belousov-Zhabotinsky en régime oscillant

Target patterns spontaneously appear in a thin layer of a Belousov-Zhabotinsky system. We report the results of a detailed statistical experimental study of these patterns, occurring when the reaction oscillates. Even from a qualitative point of view, the available theoretical descriptions are unable to satisfactorily account for our experimental data. Thus, the way in which symmetry-breaking takes place still remains a matter of guess. Increase of our knowledge of these phenomena will only be reached through further theoretical as well as experimental work.La réaction de Belousov-Zhabotinsky donne spontanément naissance en couche mince à des structures ayant la forme de cibles. On présente les résultats d'une étude expérimentale statistique de ce type de structure conduite en milieu oscillant. Aucune des approches théoriques existantes ne rend convenablement compte des observations réalisées, même du seul point de vue qualitatif. L'origine de la rupture de symétrie du milieu ne peut donc pas encore être élucidée. Un approfondissement de la théorie et un renouvellement des voies de l'expérience demeurent nécessaires