White (Mg-rich) and green (Ni-rich) clay infillings ("deweylite"/"garnierite") found in serpentine veins of faulted peridotite formations from New Caledonia consist of an intimate mixture of ...fine-grained and poorly ordered 1:1 and 2:1 layer silicates, commonly referred to as non-expandable serpentine-like (SL) and talc-like (TL) minerals. New data on the swelling and shrinking capacity of these layer silicates were gathered from X-ray diffraction (XRD) after saturation of the clay fractions with different cations (Ca2+, Li+, K+), ethylene glycol (EG) solvation, and heat treatments. Simultaneously, layer charge distribution and vacancy density, respectively, were investigated by FTIR spectroscopy on NH4-saturated clay fractions and XRD on Li-saturated clay fractions before and after heating (Hofmann Klemen treatment). Five clay infillings, with dominant 2:1 layer silicates and variable Ni contents, were selected for this study, from a large set of veinlets, according to their swelling capacity. The crystal chemistry of these samples was characterized by FTIR spectroscopy and bulk chemical analyses. The swelling ability of the clay infillings is attributed to the 2:1 layer silicates. It does not seem to be affected by the relative fraction of Mg and Ni in their octahedral sheets. In XRD patterns, the swelling ability is reflected by slight shifts of the basal reflection of the 2:1 layer silicates toward low angles for bulk samples and by splitting of the peak into two contributions for clay fractions saturated with Ca (or Li) and solvated with EG. The split increases with the swelling capacity of the sample. It originates mainly from octahedral-layer charge generated by vacant sites. Such results lead us to consider the 2:1 layer silicates of the infillings as an intimate mixture of non-expandable (TL) and expandable (stevensite) phases. In agreement with previous studies that suggested a contribution of hydrothermal processes in the alteration of serpentine species into 2:1 layer silicates, we propose that the proportion of expandable phases in the clay infillings (or vacancy sites in the octahedral sheets of the 2:1 layer silicates) could be used as an efficient means for assessing the temperature of their formation. Clay infillings mostly made of stevensite would have formed at ambient temperatures, whereas those consisting mainly of non-expandable TL would have formed at higher temperatures.
A survey of electrical, pedological and geotechnical measurements was carried out on the Marais du Poiré-sur-Velluire site (Marais Poitevin, France) in 2021 and 2022 to characterise micro-reliefs ...(often named “mottureaux” or “gilgais”), which are home to a rich biodiversity. The electrical measurements consisted in Electrical Resistivity Tomography at various investigation depths. The summary of the results presented in this paper highlights the following two elements, which may play a definite role in the genesis of these very special micro-reliefs: (a) desiccation cracks and (b) the thickness of a very soft, plastic-to-liquid clay layer in the saturated part of the soil.
Une campagne de mesures électriques, pédologiques et géotechniques a été menée dans le Marais du Poiré-sur-Velluire (Marais Poitevin, France) afin de caractériser des micro-reliefs (souvent appelés “mottureaux” ou “gilgais”) lieux d’une riche biodiversité. Les mesures électriques ont consisté à acquérir des Tomographies de Résistivité Electrique à différentes profondeurs d’investigation. La synthèse des résultats obtenus présentée dans ce papier met en lumière deux éléments pouvant jouer un rôle significatif dans la formation de ces micro-reliefs si particuliers : (a) les fissures de dessiccation et (b) l’épaisseur d’une couche d’argile très molle, plastique à liquide dans la partie saturée du sol.
•Termite mound soils have lower C but similar clay contents compared to surrounding control soils.•Soil macro-aggregates >250μm from termite mounds are less stable than control soil ...aggregates.•Stability of termite mound soil micro-aggregates <250μm is reduced in Ferralsol but not in Vertisol.
Termites are considered soil engineers due to their effects on soil properties in tropical ecosystems, which include the production of biogenic aggregates with different physical and chemical properties to the surrounding environment. How termites influence the dynamics of aggregates on the soil surface is still poorly understood. In this study, we sampled 50–250, 250–2000 and >2000μm soil aggregates from the wall of termite mound nests produced by Odontotermes obesus (Blattoidea, Macrotermitinae subfamily) in a Ferralsol and in a Vertisol in Southern India and analyzed their stability in water and to ultrasonic agitation. Our study shows that the influence of termites on the stability of soil aggregates varies depending on the properties of soil. The concentrations in C and N were lower in termite mound soils compared to the control soil aggregates in the Ferralsol for all the soil aggregate size fractions whereas in the Vertisol, the C and N contents were only lower in soil aggregates >2000μm (i.e., no significant difference for aggregates <2000μm). No difference in clay, silt or sand content was measured between the termite mound wall and the control soil. Soil aggregate stability was reduced for all size categories of aggregate in the Ferralsol but it was only reduced for soil macro-aggregates >250μm in the Vertisol. Since micro-aggregates <250μm are considered to predominantly protect soil organic matter in the long term pools, the impact of termites on C protection and nutrient cycling may be higher in Ferralsols than in Vertisols.
Abstract
Local waterlogging often occurs on the steep slopes of clayey–calcareous soils in southwestern France, causing nutrients and pollutants transfer to the river bodies and reduced ecosystems ...services. These soils developed in the Miocene molassic hill formation and are generally impermeable with abundant traces of hydromorphy and heterogenous spatial distribution. This article aims to describe the hydrological functioning of these soils, based on a cross analysis of pedological, hydrological, and geophysical characterizations. Our experimental site is the catchment area located in Auradé (southwestern France). Here, we analyze the flows at the outlet of the studied watershed together with piezometric and climatic monitoring from September 2020 to September 2021. We show that the hydrological year is divided into three phases: first, a soil recharge phase with an effective rainfall of about 100 mm; second, a saturation phase, when 80% of the effective precipitation is drained mostly by runoff and hypodermic flows; third, a drying phase. Soil waterlogging events usually occur during the saturation phase. They are due to several forms of flow: surface runoff associated with return flow, hypodermic flow caused by the presence of soil layers with lower hydraulic conductivity in the subsurface (swelling clays and plowing sole) and groundwater flow with intermittent connection of the soil water table in the hillside to the alluvial groundwater table. We also conducted independent seismic refraction tomography analyses that validate localized waterlogging patterns along the catchment and open the way to spatializing areas with high waterlogging potential at the scale of the study plot.
Core Ideas
An interdisciplinary approach (pedology, hydrology, and geophysics) highlights flow paths in hilly calcisols.
Seismic geophysics reveals heterogeneities of the molasse material that drives intermittent downslope connectivity.
Soil porosity value around 100 mm both corresponds to the soils water adsorption and water supply capacities.
The sand lens acts like a local captive aquifer for a period of 4 months starting in winter.
Abstract Furnas is a small and not well-known copper sulfide deposit in the northern Carajás mineral province (Pará State, Brazil). Mineralogical and geochemical studies were performed on three ...weathered samples in order to verify the presence of copper in the lateritic minerals. According to these Cu-bearing minerals (malachite, e.g.), the weathered ore can be exploited. X-ray diffraction (XRD), Scanning Electron Microscopy (SEM) and Fourier Transformed Infrared (FTIR) spectroscopy analyses have shown that the copper is mainly associated to cryptomelane and to clay minerals and, although goethite composes from 40 to 50% of the samples (weight %), less than 0.1% of the total Cu is associated to it. Based on the results, the weathering sequence could be established; the alteration processes were responsible for the dissolution of the copper primary sulfides; the Cu released by these sulfides is, afterwards, incorporated in biotites and vermiculites, following the gneiss schistosity. Afterwards, the biotites altered to an interstratified 10-14 Å (biotite-smectite-vermiculite) and subsequently to an Al-Fe-Cu smectite (nontronite); finally, smectite was altered to kaolinite and the Cu was leached.
ABSTRACT Ferralsols ( Latossolos ) should contain few or no 2:1 clay minerals and have low potassium (K) contents, and consequently low levels of non-exchangeable K forms are expected. The aim of ...this study was to evaluate how the clay mineralogy of a Ferralsol affects the soil K dynamics in response to K fertilization during cropping and whether the clay mineralogy was altered due to successive crops and K fertilization. A tropical Brazilian Ferralsol under field conditions was sampled (0.00-0.20 m) in contrasting K fertilization plots: no K application (control plot) and 3,200 kg ha-1 applied K2O fertilizer. These two treatments were submitted at eight different crop cycles, performed in pots under greenhouse conditions, and fertilized with 0, 30, and 90 mg kg-1 K2O before each crop cycle. The biomass K, exchangeable K, non-exchangeable K, and structural K contents were determined after each crop cycle. At the end of the experiment, the presence of 2:1 clay minerals with hydroxy-aluminum interlayered in the soil clay fraction was verified, which ensured K adsorption in a form available to plants when K fertilizer was added. Cropping without K fertilization resulted in limited crop yields and exhausted the exchangeable and non-exchangeable K soil reserves. The previous K fertilization history influenced the soil K reserve and its availability to plants in the Ferralsol studied. The crops without K addition decreased the proportion of 2:1 hydroxy-Al interlayer minerals in the soil in relation to the kaolinite clay minerals.
Soil management and crop rotation are key factors in controlling the accumulation of C and N in the soil profile, but their long-term effect remains poorly understood for deep soil layers, especially ...in subtropical conditions. Using a long-term experiment (26-years), this study aimed to evaluate the effect of different soil management systems associated with different winter cover crops on C and N accumulation in a very clayey (72 % clay) soil up to 1 m deep. Two tillage systems conventional tillage (CT) and no-tillage (NT) were cultivated with eight winter cover crops (black oat, rye, common vetch, hairy vetch, oilseed radish, wheat, blue lupine, and fallow) in a subtropical Oxisol from Southern Brazil. Soil samples were taken in eight soil layers up to 1.00 m soil depth after 26 years of experiment and, also from an adjacent native forest. After forest clearing, the C stock in the 0.00-0.20 m soil layer was reduced by 45 % in only 10 years (from 1976 to 1986) of soil tillage. Twenty-six years after the beginning of the experiment, C and N stock in 0.00-0.20 m soil layer were 13 and 20 % higher in NT compared to CT, with the greatest differences in C and N content observed in the 0.00-0.05 m layer. When associated with winter cover crops, NT accumulated 0.6 and 0.06 Mg ha-1 yr-1 more C and N than CT with winter fallow in the 0.00-0.20 m soil layer. No-tillage and CT recovered 95 and 83 %, respectively, of the C stock found in the 0.00-0.20 m layer from the native forest. However, in the 0.00-1.00 m soil layer, the positive effect of NT on soil C accumulation compared to CT was diluted, and no clear effect of NT was verified. Moreover, no difference in winter cover crops on soil C and N stocks were observed in all soil layers, possibly due to their similar residues input (3.3-4.9 Mg ha-1 yr-1). No-tillage associated with high biomass input through winter cover crops promoted a faster recovery of soil C and N stock than in CT and, therefore, is an efficient tool to improve soil C and N accumulation even in Oxisols with high clay content.
Phosphorus (P) nutrition is essential to both plant yield and soil organic matter (SOM) input. However, continuous extraction of P by plants and biomass harvesting can lead to soil P stock depletion, ...a reduction in crop yields and ultimately a reduction in organic matter input to the soil. In this work, we analysed P, C and N stock trends in the 0-30 cm topsoil layer cultivated with permanent cropland (CC) and mowed permanent grassland (GG) for 13 years. In addition, we characterized the changes in P organic forms by using
31
P-NMR. The results showed that the amount of P exported within 13 years was 10% greater in GG than in CC (295 and 268 kg ha
-1
, respectively). The total P stocks decreased under both the CC and GG management systems (0.30 and 0.25 Mg ha
-1
, respectively). This depletion was mainly observed in total Pi forms, which recorded reductions of 0.75 and 0.29 Mg ha
-1
in GG and CC, respectively. The total Po stock increased by 42.6% in GG; these results were consistent with the increase in C and N stocks in GG (2.6 and 0.19 Mg ha
-1
, respectively) and their reduction in CC (-4.2 and -0.38 Mg ha
-1
, respectively). Although P depletion mainly affected the P pool presenting the highest lability (labile P), this depletion did not have a negative effect on plant yield after 13 years due to the buffering capacity of P pools presenting less lability (moderately labile P). Mowing permanent grasslands led to a change in the pool of labile P from inorganic to organic forms and an increase in soil C and N stocks. Based on the
31
P-NMR technique, permanent grasslands significantly reduced α-glycerophosphate and increased myo-IHP and adenosine monophosphate more than the permanent cropland. Although there was no significant decrease in productivity, the depletion of available P should be monitored over time, especially in mown permanent grassland crops, to prevent potential nutrient stress.
ABSTRACT Phosphorus (P) fractionation is a suitable procedure to ascertain P lability in sediments and is able to distinguish sources of P under different soil management practices in a catchment. ...Brazil is the second largest producer and the largest exporter of tobacco in the world. Inadequate management of cultivated areas exposes the soil to erosion processes, accelerating the transfer of sediment and P to water bodies, which leads to eutrophication. We evaluated the P forms in suspended sediments collected at two rainfall events in the stream of a small catchment in the state of Rio Grande do Sul. The samples were collected upstream and downstream areas in three sub-catchments with different degrees of anthropogenic pressure and in three phases of the hydrograph in the catchment outlet. The first rainfall event occurred during the fallow period, and the second one, during the period of transplanting the tobacco crop. The sediment P forms were evaluated by successive extractions, following the Hedley method. The results showed that an increase in anthropogenic pressure leads to an increase in total inorganic P and a decrease in the levels of organic C and total organic P in sediments. In the control area, the quantity and quality of the eroded material remained the same in both rainfall events. The levels of total P in sediment alone were not sufficient to evaluate the influence of the soil management practices prevalent in each sampling period. However, P fractionation shows that during the tobacco transplanting period, P in sediments was mainly in labile fractions, and rainfall during this period was more likely to promote the eutrophication process. Sediments carried in runoff during the tobacco transplanting period have larger amounts of available P than those borne during rainfall in the fallow period.
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