Différenciation toposéquentielle et transformations morphologiques d'un sol brun de Bretagne

Cet article présente l'étude d'une toposéquence, située dans la basse forêt de Paimpont (Rennes), qui associe un domaine podzolique à l'amont, un domaine médian à sol brun lessivé et un domaine aval avec un sol à caractères planosoliques. Les observations macromorphologiques et micromorphologiques mettent en évidence une progression latérale du podzol et du sol planosolique aux dépens du sol brun. Il s'agirait d'un système de transformation avec deux systèmes transformants : l'un centrifuge (podzol), l'autre centripète (planosol

Influence of Radar Frequency on the Relationship Between Bare Surface Soil Moisture Vertical Profile and Radar Backscatter

International audienceThe aim of this letter is to discuss the influence of radar frequency on the relationship between surface soil moisture and the nature of radar backscatter over bare soils. In an attempt to address this issue, the advanced integral equation model was used to simulate backscatter from soil surfaces with various moisture vertical profiles, for three frequency bands, namely, L, C, and X. In these computations, we investigated the influence of the vertical heterogeneity of soil moisture on the characteristics of the backscattered signals. The influence of radar frequency is clearly demonstrated. A database produced from Envisat ASAR and TerraSAR-X data, which was acquired over bare soils with in situ measurements of moisture content and ground surface roughness, was used to validate the utility of taking the soil moisture heterogeneity into account in the backscatter model

The use of the scintillation technique for monitoring seasonal water consumption of olive orchards in a semi-arid region

To monitor seasonal water consumption of agricultural fields at large scale, spatially averaged surface fluxes of sensible heat (H) and latent heat (LvE) are required. The scintillation method is shown to be a promising device for obtaining the area-averaged sensible heat fluxes, on a scale of up to 10 km. These fluxes, when combined with a simple available energy model, can be used to derive area-averaged latent heat fluxes. For this purpose, a Large Aperture Scintillometer (LAS) was operated continuously for more than one year over a tall and sparse irrigated oliveyard located in south-central Marrakesh (Morocco). Due to the flood irrigation method used in the site, which induces irregular pattern of soil moisture both in space and time, the comparison between scintillometer-based estimates of daily sensible heat flux (HLAS) and those measured by the classical eddy covariance (EC) method (HEC) showed a large scatter during the irrigation events, while a good correspondence was found during homogenous conditions (dry conditions and days following the rain events). We found, that combining a simple available energy model and the LAS measurements, the latent heat can be reliably predicted at large scale in spite of the large scatter (R2 = 0.72 and RMSE = 18.25Wm2) that is obtained when comparing the LAS against the EC. This scatter is explained by different factors: the difference in terms of the source areas of the LAS and EC, the closure failure of the energy balance of the EC, and the error in available energy estimates. Additionally, the irrigation efficiency was investigated by comparing measured seasonal evapotranspiration values to those recommended by the FAO. It was found that the visual observation of the physical conditions of the plant is not sufficient to efficiently manage the irrigation, a large quantity of water is lost (37% of total irrigation). Consequently, the LAS can be considered as a potentially useful tool to monitor the water consumption in complex conditions

Agrometerological study of semi-arid areas : an experiment for analysing the potential of time series of FORMOSAT-2 images (Tensift-Marrakech plain)

Earth Observing Systems designed to provide both high spatial resolution (10m) and high capacity of time revisit (a few days) offer strong opportunities for the management of agricultural water resources. The FORMOSAT-2 satellite is the first and only satellite with the ability to provide daily high-resolution images over a particular area with constant viewing angles. As part of the SudMed project, one of the first time series of FORMOSAT-2 images has been acquired over the semi-arid Tensift-Marrakech plain. Along with these acquisitions, an experimental data set has been collected to monitor land-cover/land-use, soil characteristics, vegetation dynamics and surface fluxes. This paper presents a first analysis of the potential of these data for agrometerological study of semi-arid areas

I. Déséquilibre pédobioclimatique dans les couvertures pédologiques de l'Afrique tropicale de l'Ouest et son rôle dans l'aplanissement des reliefs

Wenn sich die tropischen Bodendecken Westafrikas im bodenklimatischen Ungleichgewicht befinden bilden sie sich um. Werden sie trockeneren und ausgeprägteren Wechselklima ten als denen ihrer Entstehung unterworfen, so werden die kaolinitreichen Decken mit und ohne Panzer Opfer einer internen Auslaugung, die zu einem Material-und Volumenveriuet führt. Ausserdem erzeugen die Ober-flächenauslaugungen der Kaolinit-Panzer oder Montmorillonit -Decken an ihrer Oberfläche auegelaugte Horizonte, die die Arbeit der mechanischen Erosion vorbereiten. Auslaugungen im Innern und an der Oberfläche liegen im Wettstreit bei der Abflachung und Einebnung.When tropical pédologie mandes of Western Africa are in pedobioclimatic desequilibrium, they are transforming. The kaolinitic mantles, with or without ironcrusts, in climates drier and more contrasted than those of their genesis, are submitted to internal teachings. This results in losses of matter and volume. Moreover, the superficial teachings of kaolinitic, «ironcreted» (iron indurated), or montmo-rillonitic mantles generate superficial leached horizons. This prepares the action of mechanical erosion. Internal and superficial teachings concur in the rectification of the relief and in the leveling.Quand les couvertures pédologiques tropicales de l'Afrique de l'Ouest se trouvent en déséquilibre pédobioclimatique, elles se transforment. Soumises à des climats plus secs et plus contrastés que ceux de leur naissance, les couvertures kaoliniques, cuirassées ou non, sont victimes de lessivages internes qui provoquent perte de matière et perte de volume. De plus, les lessivages superficiels des couvertures kaoliniques, cuirassées, ou montmorillonitiques, engendrent des horizons lessivés de surface qui préparent le travail de l'érosion mécanique. Lessivages internes et lessivages superficiels concourent à la rectification du modelé et à l'aplanissement.Boulet René, Bocquier Gérard, Millot Georges. I. Déséquilibre pédobioclimatique dans les couvertures pédologiques de l'Afrique tropicale de l'Ouest et son rôle dans l'aplanissement des reliefs. In: Sciences Géologiques. Bulletin, tome 30, n°4, 1977. Géochimie de la surface et formes du relief. pp. 235-243