The intensive use for over 100 years of copper sulfate (Bordeaux mixture) to fight against mildew in vineyard soils has led to an important, widespread accumulation of Cu (100 to 1500 mg Cu kg(-1) soil). In Champagne vineyards, organic amendments are used currently to increase soil fertility and to limit soil erosion. Organic amendments may have a direct effect on the retention of Cu in the soil. To assess the influence of the organic management on the fate of Cu in calcareous Champagne vineyard soils, we studied Cu distribution (1) in the soil profile and (2) among primary soil particles, in vineyard parcels with different amendments. Amendments were oak-bark, vine-shoots and urban compost. The results were compared with the amount and the distribution of Cu in an unamended calcareous soil. Physical soil fractionations were carried out to separate soil primary particles according to their size and density. Cu has a heterogeneous distribution among soil particle fractions. Two fractions were mainly responsible for Cu retention in soils: the organic debris larger than 50 mum or coarse particulate organic matter (POM) issued from the organic amendments, and the clay-sized fraction <2 m. The POM contained up to 2000 mg Cu kg(-1) fraction and the clay fraction contained up to 500 mg Cu kg(-1) fraction. The clay-sized fraction was responsible for almost 40% of the total amount of Cu in the four parcels. POM was predominantly responsible for the differences in Cu contents between the unamended and the three amended parcels. Our results attested that methods of soil particle-size fractionation can be successfully used to assess the distribution of metal elements in soils. (C) 2001 Elsevier Science Ltd. All rights reserved.

During the drainage season, significant quantities of suspended matter can be exported from a drain collector. Their nature has been determined with a methodology linking chemical analysis, X-ray diffraction, and electronic microscopy associated with image analysis. The majority of these particles are smaller than 200 nm. They are composed of 2:1 phyllosilicates and iron particles usually in amorphous form. Cs-137, phosphorus and organic matter clearly demonstrate the superficial origin of these particles. Drainage modifies natural leaching of soil by exporting definitively particles from the soil profile. (C) 2000 Academie des sciences/Editions scientifiques et medicales Elsevier SAS.

The current soil dynamics of a podzol-oxisol climosequence located in Tahiti on basaltic and pyroclastic parent rocks has been investigated using the ''test-mineral'' technique. The test-mineral, a vermiculite with a high exchange capacity (161 meq/100 g) was placed in recoverable bags in the A and B horizons of three members of the sequence, for periods of 1 to 3.5 years.Changes in the chemistry and mineralogy, enabling complexing acid environments to be distinguished from non-complexing, were determined following the in situ reaction with natural soil leachates. A set of leachates from the same horizons were collected and chemically analysed at the end of 3.5 years. The results indicate that the current acid environment is only weakly complexing. This suggests that the podzolisation processes which led to the development of a unique A2 horizon containing gibbsite, anatase and rutile, and a placic horizon, in the upper podzol member of the sequence, is no longer operating.

The ways through which ectomycorrhizal fungi benefit tree growth and nutrition have not been totally elucidated. Our study was therefore aimed at assessing fungal access to soil exchangeable and stable mineral reserves. The growth of different ectomycorrhizal fungi in bi-compartment Petri dishes with NH4+- or Ca-saturated vermiculite led to cation exchange reactions and to crystal lattice weathering. The presence or absence of soluble NH4+ or Ca did not seem to affect fungal mobilization potential. Oxalic acid appears to be involved in vermiculite weathering by Paxillus involutus and Ca ions could limit the acid dissolution of Ca-saturated vermiculite. The quantitative significance of such cation mobilization and mineral weathering still has to be assessed in situ and in association with ectomycorrhizal plants.

In studies on the fate of aluminium in the environment, nontronite and saponite have been obtained by synthesis in reducing alkaline conditions close to those prevailing in poorly drained soils developed from limestones. The two minerals obtained have different structures and organizations corresponding to two different growth and/or maturation mechanisms. High-resolution transmission electron microscopy of ultrathin sections of a synthetic aluminous nontronite embedded in resin showed the presence of crystallites consisting of two to ten co-terminating parallel layers, indicating synchronous growth. Electron diffraction showed that the individual crystallites had hk-ordering, i.e., orientation of layers with respect to the six-fold pseudosymmetry of the unit cell. Deposits of a synthetic saponite included hk-ordered crystallites and crinkled films with turbostratic stacking. The two saponite phases had slightly different b dimensions. Lattice fringe images of sections of saponite embedded in resin showed a high angular disorientation of the layers in the stacking direction, suggesting multiple nucleation and growth of individual layers, subsequently aggregated with imperfect parallelism. Exploration of the synthetic conditions of the aluminous nontronite indicated that calcium was essential for an hk-ordered product. Syntheses using potassium or sodium hydroxides and carbonates for pH control gave poorly organized nontronites. Hydrazine was not essential for nontronite formation, but better crystallized products—judging by their IR spectra—were obtained in its presence by maintaining reducing conditions in the early stages of synthesis. Attempts to prepare ferruginous beidellites under similar conditions to those in which aluminous nontronites formed were unsuccessful.

Cryo-scanning electron microscope studies of modern stromatolites from brackish to hypersaline lakes of the dry equatorial Pacific area show that, similarly to French Polynesian stromatolites (kopara), three-dimensional organic networks inherited from microbial envelopes are involved in the development of sediment microstructure an carbonatation. These results suggest that such networks may be similarly involved in the formation of other microbial sediments, and may have also participated in the genesis of ancient stromatolites, notably those which are predominant in the Precambriam rock record

Cryo-scanning electron microscope studies of modern stromatolites from brackish to hypersaline lakes of the dry equatorial Pacific area show that, similarly to French Polynesian stromatolites (kopara), three-dimensional organic networks inherited from microbial envelopes are involved in the development of sediment microstructure and carbonatation. These results suggest that such networks may be similarly involved in the formation of other microbial sediments, and may have also participated in the genesis of ancient stromatolites, notably those which are predominant in the Precambrian rock record.

With the use of Cryo Scanning Electron Microscopy (SEM performed at low temperatures) the microstructure of clay- (bentonite and kaolinite) amended and unamended loamy sand was studied. A wide range of pore sizes could be recognized in all three treatments, but pore size distributions clearly differed between the soil types. The bentonite clay was present as a very porous matrix, containing pores with an average maximum length of ∼ 3 μm, and an average minimum width of ∼ 2 μm. Pores of similar sizes were also present in kaolinite- and unamended loamy sand, but they were much less frequent. Previous results, suggesting that the protective effects of bentonite clay on the survival of introduced bacteria in soil could be caused by an increase in the number of pores with an equivalent neck diameter < 6 μm, were confirmed.

SUMMARYThe ability of the roots of rape (Brassica napus) to promote the transformation and dissolution of a phlogopite mica was studied in the rhizosphere. Rape was cropped for 1 to 32 d on 2–105 μm phlogopite as sole source of both K and Mg. The chemical balance of K and Mg revealed that rape was able to induce a significant release of interlayer‐K after 4 d, and even a significant release of octahedral‐Mg after 8 d of cropping. After 32 d, the root‐induced release amounted to 80 and 21 g kg−1 of total‐K and ‐Mg, respectively. The weathering products sampled in the close proximity of the roots were analysed by X‐ray diffractometry (XRD), and by energy dispersive X‐ray (EDX) microanalysis of resin‐embedded samples prepared for transmission electron microscopy. The XRD analysis of K‐saturated, oriented plates showed that part of the vermiculite formed by root activity behaved as a typical hydroxy‐aluminous interlayered vermiculite (HIV). The EDX microanalysis revealed that the release of interlayer‐K which occurred during the vermiculitization was compensated mostly by A1 and Mg originating from the octahedral sheet of the phlogopite. Such crystallographic and crystallochemical changes necessarily involved an acid dissolution of the mica structure, which may be related to the root‐induced pH decrease encountered simultaneously in the rhizosphere. Proton excretion by rape roots was thus the probable mechanism involved in the root‐induced irreversible transformation of the phlogopite.

Experimental studies were conducted to investigate the role of different living organisms (roots, fungi, bacteria) on clay microfabric. For this purpose various microorganisms (bacteria, fungi) and roots were allowed to grow on kaolinite or montmorillonite pastes under controlled hydric conditions (−0.01 to −102 MPa). Microstructures were studied with a cold-stage SEM, that allowed the preservation of the organizations that characterized the wet states. With fungi, three main effects were observed in moist conditions: orientation of clay particles around the cells; secretion of extracellular polysaccharides that induced local binding of clay particles, and a general packing effect by hyphae. These effects lead to a new microstructure, in the immediate surrounding of the cell, designated as a microenvironment. A modified microstructure was recognized with all species, the size depending on the size of organism. With bacteria, polysaccharide-mediated aggregation was predominant. With grass roots, modifications of the microstructure were more complex than with fungi and occurred at a larger scale. The present results thereby confirm and complete the existing models on biologically mediated aggregation in soils.

We have tested an in situ experimental method in which a cationic exchange resin, a chelating resin and a test-mineral (vermiculite) were placed in permeable bags and inserted into various soil horizons. Later, the bags were removed and the contents analysed to characterize the currently active geochemical processes in forest acid soils (Humods, Orthods, Ultisols, Oxisols, Dystrochrepts).

The changes in forest soil function due to silvicultural modifications were studied by an in situ experimental method. This method used the evolution of a test-mineral as an indicator of change in the physico-chemical environment of the soil.The processes operating in the soil can be identified with reference to laboratory data obtained on the same mineral.After 3 years in acidic soils, the test-mineral (an interstratified mineral containing vermiculite) was studied; CEC, exchangeable and non exchangeable elements, mineralogy (XRD traces), and compared with the control.The results showed that if the chemical data and the mineralogy are studied, one can characterize the effects of soil types, soil horizons and forest species. In the acid brown soils the test mineral is highly desaturated while exchangeable acidity increases. In this soil, Al is rapidly hydroxylated. The change of forest species (spruce versus mixed broadleaved) produces an important mobilization of Al and forms a more shable Al intergrate. In the podzol, the quality of Al is greater than in the acid brown soil but the formation of a very stable Al intergrade mineral was not observed. The change of forest species (spruce versus beech) tends to produce the same relative effect as observed in the acid brown soil.The processes of soil function can be defined as follows:- acidolysis is the processes which discriminates the function of acid brown soils;- acido-complexolysis characterizes the A1, A2 horizons of the podzolic soils.We can identify the mechanisms involved in the effect of species on soil function; for example the spruce increases acidity which mobilizes more Al and which tends to form a more stable Al integrate than the broadleaved species; there is a strong interaction between soil and species. Statistical analyses show the level of significance of the effects (soils, species) and allow a clear vizualisation of the results. This method with its unique experimental reference allows us to compare numerous situations and to characterize the mechanisms of soil function in relation to soil type and species.The different processes of soil function that we have recognized, correspond to very different aluminium speciation and cation distribution on the CEC, and consequently to different behaviour for the nutrition and the development of forest species.

A ferrallitic soil sequence from red to yellow developed on carbonate rocks in Cuba is studied. Clay content is very high (80 to 90 %) and composition differs mainly in the relative proportion of hematite and goethite. The main modification concerns the organization of constituents. Kaolinite crystallites are very small and independent in yellow soil resulting in a massive fabric. These crystallites are associated in red soil giving one μm aggregates and micropeds (500 μm). Higher Al content (TEM + microprobe) suggests that the cement is more an Al than an Fe coating. Soil compaction and consequent waterlogging are likely to be responsible for such a soil structure evolution. CEC, specific surface and porosity are different in the two kinds of soils and then all the physical properties.

SUMMARYA mica was inserted into the soil at four sites to try to identify, in situ, the physico‐chemical changes in the soil caused by the introduction of different tree species, and especially conifers. Changes in the chemistry and mineralogy of the mixed‐layered mica, mica‐chlorite, vermiculite, after 1 1/2 and 31/2 years in the soil, showed good differentiation between soil horizons and between soil types. Differences due to tree species were present, but small. The mechanisms of mineral evolution can be defined with reference to experimental data obtained in the laboratory. In litter layers, the mica‐chlorite sheet was transformed into a mica‐vermiculite, and exchangeable cations predominated on the exchange sites. In the organo‐mineral horizons, changes varied depending on the soil type: in the podzol, transformation was similar to that in the litter layers, but in the sol brun acide, changes were dominated by the Al fixation on the exchange sites and its rapid hydroxylation which blocks these sites, leading to the formation of Al intergrade minerals.Different tree species produced deviations linked to their ability to cycle cations, and also to the different organic materials produced which can attack the mineral.The method has the potential to define the present soil environment and weathering processes, but it needs a more complete experimental design and the use of statistics to clarify the effects of the parameters and their interactions.

Maghemite with an unusual habit was identified in the sandy fraction of two Alfisols and one Ultisol by X-ray and electron diffraction. Hematite was also present. Morphological analyses by scanning and transmission electron microscopy showed needle-like particles of maghemite with average lengths of 200–500 nm depending on the degree of the crystallinity. Those particles are arranged in star-like patterns as shown by ultrathin sections. Experimental synthesis of maghemite was successfully attempted in the presence of quartz sand with the freshly-formed crystals displaying the same particular morphology. Formation of acicular maghemite catalysed by quartz surfaces is, therefore, postulated.