Influence of Clay Fraction and Mineral Composition on Unsaturated Characteristics of Cohesive Foundation Soil in Airports

Taking unsaturated clay foundation soil of an airport project in Hefei as the research object, the effects of particle gradation and mineral composition on the unsaturated soil properties were analyzed through two kinds of tests. The results show that there is a good correlation between the residual water content and the clay fraction or silt fraction content in the grading, and the residual water content has a significant positive linear correlation with the clay fraction content, but a negative linear correlation with the silt fraction content. Residual matric suction has a nonlinear correlation with clay fraction or silt fraction content in gradation, which has a significant nonlinear negative correlation with clay fraction content and a positive nonlinear correlation with silt fraction content. The residual water content and the residual matric suction have obvious linear relationship with the content of montmorillonite but have no obvious correlation with the content of illite. The water-storage coefficient of unsaturated airfield foundation soil decreases exponentially with the increase of clay content and montmorillonite content.

Physical and Chemical Indicators of Meadow Brown Soils

The research has established that the carbonate content of meadow brown soils in the upper and lower horizons varies between 1–9–11%. Where in, the calcium content reaches 85–90%. The content of physical day and silt fraction is 42–75% and 24–36% respectively and is concentrated mainly in the middle part of the profile.

DISTRIBUTION OF SILT AND MOLE RAT SOD PILES ON THE PROFILE OF AGRICULTURAL SOILS OF CATENAE OF DIFFERENT PERIODS OF AGRICULTURAL DEVELOPMENT OF THE CENTRAL FOREST STEPPE

The work is devoted to the study of the granulometric composition of soils of 120-year and 240-year-old agricultural development of the meadow-steppe landscape on the example of the Belgorod region. In the lateral distribution of the silt fraction contained in the arable horizon, a significant increase of its share was found in the lower parts of the soil catenae of 120-year-old arable land; as for 240-year-old arable land, lateral fluctuations of the silt fraction are less noticeable. Average values of the silt content along the slope profiles of arable land of 240 years of age showed a local maximum of silt adjacent to the subsurface horizon. An inverse correlation was found for slopes on 120-year-old arable land, namely, the fact that the percentage of the depth silt fraction increased did not lead to an increase of the same fractions in the near-arable layer. In the soil sections of the studied catenae, numerous mole rat sod piles were found, especially many of them were detected at the depth of up to one meter. The average area occupied by mole rat sod piles on the walls of the average section is 80-90% on 120-year-old arable land and 70-80% on 240-year-old arable land. Mole rat sod piles occupy 30-40% of the walls of the soil sections on the soils of the background catenae. Mole rat sod piles are more common in the soils of the catenae of the northern slopes - both for 120-year-old and 240-year-old arable land.

Kaolinite deposits in the upper Iguaçu river, Brazil: formation and mineralogical attributes

Kaolinite (Kt) is the most studied mineral, being widely used in the ceramic, pharmaceutical and cellulose industries, in addition to being the main soil mineral in the world. Found in different parts of the planet, it differs in genesis and may be formed as a result of local weathering of the rocks, occurring in the silt fraction; and also due to the mineral's neogenesis with a predominance of clay-sized particles. The plain of upper Iguaçu river has the largest kaolinitic deposit in the south of Brazil and it’s formation raised doubts if this kaolin was transported or formed in situ due the high organic matter in the alluvial plain. To elucidate the origin of kaolin deposits, we sampled a possible font of the mineral, in the mountains of Serra do Mar and sampled two tubes that reach 4 m depth in the upper Iguaçu plain. We performed textural analysis, organic carbon, X-ray diffraction, Kt crystallography in silt and clay fractions, thermal analysis (TDA/TG) to quantify Kt and Gb in the clay fraction and scanning electron microscopy (SEM) with dispersive energy spectroscopy (EDS). The TDA/TG analysis demonstrated that saprolite has 66% of the kaolinite found in the plain. The XRD analysis shows a significant presence of mica (Mc) in all samples of the silt fraction, both in Serra do Mar and in the plain. In SEM/EDS, crystals with planar growth are observed, and the presence of pseudomorphic Mc-Kt in the silt fraction of all analyzed samples, with emphasis on the tubes sample with the crystal having almost twice the size of that observed in the saprolite sample from Serra do Mar, allowing to infer that the Kt of the silt fraction of the wetland soils were formed on site by the diagenesis of mica particles. The results obtained in this work indicate that the kaolinitic material found in the wetland of the upper Iguaçu plain is the result of weathering processes in the wetland itself, evidenced by the large pseudomorphs found, even greater than those observed in Serra do Mar.

Influence of trees and associated variables on soil organic carbon: a review

The level of soil organic carbon (SOC) fluctuates in different types of forest stands: this variation can be attributed to differences in tree species, and the variables associated with soil, climate, and topographical features. The present review evaluates the level of SOC in different types of forest stands to determine the factors responsible for the observed variation. Mixed stands have the highest amount of SOC, while coniferous (both deciduous-coniferous and evergreen-coniferous) stands have greater SOC concentrations than deciduous (broadleaved) and evergreen (broadleaved) tree stands. There was a significant negative correlation between SOC and mean annual temperature (MAT) and sand composition, in all types of forest stands. In contrast, the silt fraction has a positive correlation with SOC, in all types of tree stands. Variation in SOC under different types of forest stands in different landscapes can be due to differences in MAT, and the sand and silt fraction of soil apart from the type of forests.

Distribution of silty fraction and slurry by profile of arable soils of the central forest-steppe

The work is devoted to the study of granulometric composition of soils of 120-year and 240-year agricultural development of meadow-steppe landscape on the example of Belgorod region. In the lateral distribution of the silt fraction contained in the arable horizon, a significant increase in its proportion in the lower parts of the soil catenas of the 120-year arable, for the 240-year arable the lateral variations of the silt fraction are less noticeable. The averaged values of silt content over slope profiles of 240-year arable land showed local maximum of silt confined to subsoil horizon. An inverse relationship was found for slopes on 120-year-old arable land, namely the fact that the percentage of silt fraction increases at depth does not lead to an increase of the same fraction in the subsoil layer. Numerous blindfolds were found in the soil sections studied by caten, especially many of them were detected at a depth of up to one meter. Average area occupied by mole crusts on the walls of averaged transects is 80-90% on the 120-year arable and 70-80% on the 240-year arable. On soils of background catenas, 30-40% of the walls of soil transects are occupied by mole-rats. Blistergrasses are more often found in soils of catens of northern exposition - both 120-year and 240-year arable land.

The manifestation of VIS-NIRS spectroscopy data to predict and map soil texture in the Triffa plain (Morocco)

The use of standard laboratory methods to estimate the soil texture is complicated, expensive, and time-consuming and needs considerable effort. The reflectance spectroscopy represents an alternative method for predicting a large range of soil physical properties and provides an inexpensive, rapid, and reproducible analytical method. This study aimed to assess the feasibility of Visible (VIS: 350-700 nm) and Near-Infrared and Short-Wave-Infrared (NIRS: 701-2500 nm) spectroscopy for predicting and mapping the clay, silt, and sand fractions of the soils of Triffa plain (north-east of Morocco). A total of 100 soil samples were collected from the non-root zone of soil (0-20 cm) and then analyzed for texture using the VIS-NIRS spectroscopy and the traditional laboratory method. The partial least squares regression (PLSR) technique was used to assess the ability of spectral data to predict soil texture. The results of prediction models showed excellent performance for the VIS-NIRS spectroscopy to predict the sand fraction with a coefficient of determination R2 = 0.93 and Root Mean Squares Error (RMSE) =3.72, good prediction for the silt fraction (R2=0.87; RMSE = 4.55), and acceptable prediction for the clay fraction (R2 = 0.53; RMSE = 3.72). Moreover, the range situated between 2150 and 2450 nm is the most significant for predicting the sand and silt fractions, while the spectral range between 2200 and 2440 nm is the optimal to predict the clay fraction. However, the maps of predicted and measured soil texture showed an excellent spatial similarity for the sand fraction, a certain difference in the variability of clay fraction, while the maps of silt fraction show a lower difference.

Larger contribution of non-protonated aromatics for organic matter in subsoil than topsoil horizons in Brazilian Ferralsols

<p>Several processes are involved in soil organic matter (SOM) formation and turnover across the soil profile. Interestingly, while deep soil C appears to turn over very slowly, it remains unclear whether this trend is related to the molecular chemistry of SOM retained therein or its interaction with the mineral matrix. Besides, the extent to which the molecular chemistry of SOM is related to the chemistry, amount, and frequency of C inputs in topsoil and subsoil horizons remains unclear. We addressed these questions by collecting soil samples from three deep Ferralsols (a Gibbsic, a Ferritic, and a Haplic Ferralsol) across the Brazilian Cerrado to include samples with distinct texture classes and mineralogical combinations. Interestingly, the vegetation of the Brazilian Cerrado is characterized by different proportions of trees and grasses, implying different depth of rooting. Moreover, the Cerrado biome is subjected to frequent fire events, which could affect the input rate and the chemistry of C added to the soils. At each site, samples were taken from topsoil (0–10 cm) and subsoil horizons (60–100 cm) and incubated with a double-labeled (<sup>13</sup>C and <sup>15</sup>N) eucalypt litter for 12 months under laboratory conditions. After the incubation, the samples were submitted to physical fractionationation to isolate SOM within the particle-size fractions (PSF) greater and smaller than 53 µm. Subsequently, we quantified the total C and N remaining in these PSF. Subsamples of the clay+silt fraction (<53 µm) were treated with a 10% HF solution to concentrate SOM. The molecular composition of SOM within the HF-insoluble fraction was assessed by <sup>13</sup>C/<sup>15</sup>N Nuclear Magnetic Resonance (NMR) spectroscopy by applying a multi/cross-polarization (multi/CP) pulse sequence, yielding a quantitative solid-state magic-angle spinning (MAS) <sup>13</sup>C/<sup>15</sup>N NMR. After the incubation, litter-C was retained at approximate proportions in both PSF evaluated, while a larger fraction of the litter-N was concentrated within the clay+silt fraction. Based on the multi-CP MAS NMR results, carbohydrates (65–110 ppm) accounted for most of the total C forms identified in the HF-insoluble fraction, regardless of soil type, soil depth, and plant litter addition. In topsoil, differences in the molecular chemistry of SOM between samples treated with plant litter and the controls were small. Otherwise, plant litter inputs to subsoil led to major changes in the chemistry of SOM, with a substantial reduction in the proportion of non-protonated aromatics and the aromaticity degree of SOM. Although observed in the topsoil, this effect was much less pronounced for the three Ferralsols evaluated. In addition, following eucalypt litter addition the molecular composition of SOM in topsoil and subsoil tended to converge, becoming enriched in alkyl-C (0–46 ppm), carboxylic and/or amide groups (160–190 ppm for <sup>13</sup>C and 120 ppm for <sup>15</sup>N-NMR). Our results suggest that in topsoil, SOM molecular chemistry is consistent with a continuous supply of fresh plant litter. Otherwise, the deep burial of plant litter appears to be less relevant for SOM formation in subsoil horizons, where the accumulation of charred/pyrogenic materials are significant.</p>

Soil thermal properties of forest biogeocenoses in steppe zone as a diagnostic indicator of their soil genesis

Soil is a specific natural body, which is characterized by a number of features due to which it differs from living organisms and rocks. One of these features is its thermal properties. The most important thermal properties of the soil are thermal conductivity, thermal capacity and thermal diffusivity, which reflect the specific features of the set of properties inherent in different soils. As a result of the studies, the existence of a direct relationship between the values of thermal conductivity and thermal diffusivity of Calcic Chernozem and the content of the silt fraction in them, as well as between the thermal capacity and the content of organic matter in them. The established relations do not appear clearly in Luvic Chernozem and Chernic Phaeozem. The maximum thermal properties for Luvic Chernozem and Chernic Phaeozem were found in the eluvial horizon, which in the lower part borders on the illuvial horizon. The eluvial horizons of Luvic Chernozem and Chernic Phaeozem are characterized by lower thermal properties compared with the illuvial horizons. The thermal properties of soils can be used to clarify the distribution characteristics of the silt fraction and organic matter along the profile, as well as determination of the intensity of eluvial-illuvial processes. The establishment of these soil features is an important characteristic of their soil genesis, which is especially important for chernozem soils under forest vegetation.