L’altération des formations glauconieuses dans le vignoble du Val de Loire : quelques aspects de la libération du fer et application agronomique

Dans le vignoble du Val de Loire les terrains sédimentaires contenant des niveaux riches en glauconie sont relativement abondants. Le bon comportement agronomique de la vigne plantée dans ces sols, en particulier vis-à-vis de la chlorose ferrique, nous a incités à entreprendre une étude minéralogique et chimique de l’altération des matériaux glauconieux. En milieu non carbonaté, il y a déstabilisation de la glauconie avec passage à un plasma argileux très abondant, riche en smectites ferrifères et interstratifiés. En milieu carbonaté, l’altération est beaucoup moins poussée du fait de la présence de calcium. Au cours de l’altération, il y a libération du fer et du potassium. Une grande partie du fer se trouve à l’état facilement extractible dans les horizons riches en interstratifiés et smectites ferrifères. Des essais de cinétiques d’extraction montrent que la libération du fer à partir de ces matériaux est constante avec absence de palier d’extraction.Glauconeous rocks are numerous in the Loire Valley vineyards. When vine is planted in calcareous soils derived from glauconeous chalks, little or no lime-induced chlorosis is observed. In order to explain this, we have made a mineralogical study of two types of glauconeous profiles (calcareous and non-calcareous profiles), with special reference to the behaviour of iron. In the non-calcareous medium, weathering of the glauconite began by a loss of potassium and iron. We then obtained a layer of « glauconeous plasma » and « secondary clayey plasma ». The « glauconeous plasma» layer was composed of smectites with Fe interlayers. In the calcareous medium, glauconite weathering was slight because the presence of calcium limits the alteration of glauconite. A major part of the iron was easily extractable by complexing products or by water from the Fe smectites horizons. Kinetics curves showed a constant release without an iron extraction plateau

Épandages de boues d'épurations urbaines sur des terres agricoles : impact sur la composition en éléments traces des sols et des grains de blé

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Early Detection and Correction of Cerebral Desaturation With Noninvasive Oxy-Hemoglobin, Deoxy-Hemoglobin, and Total Hemoglobin in Cardiac Surgery: A Case Series.

Regional cerebral oxygen saturation (rS o2 ) obtained from near-infrared spectroscopy (NIRS) provides valuable information during cardiac surgery. The rS o2 is calculated from the proportion of oxygenated to total hemoglobin in the cerebral vasculature. Root O3 cerebral oximetry (Masimo) allows for individual identification of changes in total (ΔcHbi), oxygenated (Δ o2 Hbi), and deoxygenated (ΔHHbi) hemoglobin spectral absorptions. Variations in these parameters from baseline help identify the underlying mechanisms of cerebral desaturation. This case series represents the first preliminary description of Δ o2 Hbi, ΔHHbi, and ΔcHbi variations in 10 cardiac surgical settings. Hemoglobin spectral absorption changes can be classified according to 3 distinct variations of cerebral desaturation. Reduced cerebral oxygen content or increased cerebral metabolism without major blood flow changes is reflected by decreased Δ o2 Hbi, unchanged ΔcHbi, and increased ΔHHbi Reduced cerebral arterial blood flow is suggested by decreased Δ o2 Hbi and ΔcHbi, with variable ΔHHbi. Finally, acute cerebral congestion may be suspected with increased ΔHHbi and ΔcHbi with unchanged Δ o2 Hbi. Cerebral desaturation can also result from mixed mechanisms reflected by variable combination of those 3 patterns. Normal cerebral saturation can occur, where reduced cerebral oxygen content such as anemia is balanced by a reduction in cerebral oxygen consumption such as during hypothermia. A summative algorithm using rS o2 , Δ o2 Hbi, ΔHHbi, and ΔcHbi is proposed. Further explorations involving more patients should be performed to establish the potential role and limitations of monitoring hemoglobin spectral absorption signals

La cartographie des sols à moyennes échelles en France métropolitaine.

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