A method to predict the soil susceptibility to compaction of surface layers as a function of water content and bulk density

International audienceIdentifying the vulnerability of soils to compaction damage becomes an increasingly important issue in the planning and execution of farming operations. Soil compaction models are efficient tools for predicting soil compaction due to agricultural field traffic. Most of these models require the knowledge of the stress/strain relationship, as well as the mechanical parameters and their variation with different soil physical properties. Because the soil compaction depends on its water content, bulk density and texture, a good understanding of the relation between them is essential for defining suitable farming strategies according to climatic changes. In this work we propose a new pedotransfer function for 10 French representative soils collected from cultivated fields, a vineyard and forests. We investigate the relationship between soil mechanical properties and easily measurable soil properties as well as water content and bulk density. Confined compression tests were performed on remoulded soils of a large range of textures at different initial bulk densities and water contents. The use of remoulded samples allowed us examining a large range of initial conditions with low variability of measurement. A good linear regression was obtained between soil precompression stress, compression index, initial water content, initial bulk density and soil texture. The higher the clay content, the higher the soil capacity to bear higher stresses at higher initial water content without reaching severe compaction state. The initial water content played an important role in clayey and loamy soils. In contrast, for sandy soils, the mechanical parameters were less dependent of initial water content but more related to the initial bulk density. These pedotransfer functions are expected to hold for soils of surface layers with tillage but further measurements on intact samples are needed to tests their validity

Antiretroviral-naive and -treated HIV-1 patients can harbour more resistant viruses in CSF than in plasma

Objectives The neurological disorders in HIV-1-infected patients remain prevalent. The HIV-1 resistance in plasma and CSF was compared in patients with neurological disorders in a multicentre study. Methods Blood and CSF samples were collected at time of neurological disorders for 244 patients. The viral loads were >50 copies/mL in both compartments and bulk genotypic tests were realized. Results On 244 patients, 89 and 155 were antiretroviral (ARV) naive and ARV treated, respectively. In ARV-naive patients, detection of mutations in CSF and not in plasma were reported for the reverse transcriptase (RT) gene in 2/89 patients (2.2%) and for the protease gene in 1/89 patients (1.1%). In ARV-treated patients, 19/152 (12.5%) patients had HIV-1 mutations only in the CSF for the RT gene and 30/151 (19.8%) for the protease gene. Two mutations appeared statistically more prevalent in the CSF than in plasma: M41L (P = 0.0455) and T215Y (P = 0.0455). Conclusions In most cases, resistance mutations were present and similar in both studied compartments. However, in 3.4% of ARV-naive and 8.8% of ARV-treated patients, the virus was more resistant in CSF than in plasma. These results support the need for genotypic resistance testing when lumbar puncture is performe

Disponibilité des xénobiotiques organiques dans les sols

National audienc

Elastic properties of network of fractal clusters

International audienc

Biotransformation of s-triazine herbicides and related degradation products in liquid cultures by the white rot fungus Phanerochaete chrysosporium

International audienc

Model for the flow of a yield fluid through a porous medium

Classification. Physics AbstractsInternational audienc

Biodegradation of PAHs by Trametes versicolor in presence of montanox

National audienc

Soil hydrophobicity: a contribution of diuron sorption experiments

International audienceRetention processes play a major role in the fate and impact of organic contaminants in soils. The main goal of this study was to determine the influence of soil hydrophobic properties on the retention of diuron by using plots of a long-term experiment in Versailles. We selected seven plots with pH 3.4 to 8.2 and low organic content. Sorption isotherms were obtained on soil slurries and kinetic measurements of diuron sorption were performed on undisturbed soil samples. The results showed that the Freundlich coefficient kf decreased as pH increased and that the Koc coefficient, kf/TOC, was linearly related to the contact angle measured on the clay fraction over a wide range of pH. A low initial adsorption rate and low adsorption equilibrium were observed for the plot treated with NaNO3. In this case, the structure in micro-aggregates was assumed to limit the accessibility of adsorption sites. The CaCO3 and CaO treated plots had similar organic matter contents, pHs, CECs and bulk densities, although their < 2 03BCm:C ratio differed. The higher retention of diuron in the CaCO3 plot is attributed to the higher hydrophobicity of the < 2 03BCm fraction, probably masking part of the permanent clay negative charges. Thus, in addition to the different treatments, organic matter composition and distribution should also be included as specific soil properties. We conclude that the sorption properties of pesticides such as diuron can be a good tool to obtain greater understanding of soil properties and the degree of soil hydrophobicity/hydrophilicity in particular

Influence of adsorbed polymers on the removal of mineral particles from a planar surface

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