Silicon solubilisation from soil minerals and soil by root exudate compounds

Soil mineral plays an important role in agriculture due to its ability in influencing soil physical and chemical characteristics, and therefore is important to be identified. The techniques for identifying soil minerals, such as the utilization of a polarization microscope and X-Ray Diffraction (XRD), are often laborious, time-consuming, and costly. This study aims to identify and to quantify soil clay minerals by using Hyperion EO-1 imagery and XRD methods, and to reveal the effectiveness of using satellite imagery to determine soil minerals. Spectral signatures from Hyperion EO-1 were extracted in alignment with the soil sampling coordinate locations, and spectral data processing methods such as Continuum Removal (CR), and Savitzky-Golay filtering were used to identify and to quantify minerals. The results show that hyperspectral analysis revealed distinct spectral absorption features, and it could identify kaolinite, chlorite, goethite, hematite, and plagioclase. Meanwhile, XRD analysis confirmed kaolinite and chlorite, consistent with the hyperspectral observations. A key advantage of the spectral absorption technique for raw soil was its ability to identify not only clay minerals, but also both primary and secondary minerals, such as plagioclase, hematite, and goethite, that remain unidentified when using the XRD method with iron removal pre-treatment. Although hyperspectral imagery was successful in identifying soil minerals, there are still some limitations that require further refinement, especially while conducting quantification. The findings underscored the potential of satellite-based hyperspectral analysis as a rapid alternative approach to soil mineral identification that can reduce reliance on laboratory-based methods.

The microstructural stability of soils of different geneses (steppe soils, tropical soils, and subtropical soils) developed from marine clay, loess, and weathering crusts was studied by the method of successive treatments with chemical reagents destroying the particular clay-aggregating components. The following dispersing agents were used: (1) H2O (pH 5.5), (2) 0.1 N NaCl (pH 6), (3) 0.002% Na2CO3 (pH 8.7), (4) 0.1 N NaOH (pH 11.5), (5) the Tamm reagent (pH 3.2), and (6) 0.1 N NaOH (pH 11.5). The properties of the clay subfractions obtained in the course of these treatments were studied by a set of analytical methods, including X-ray diffractometry, Mossbauer spectroscopy, and magnetic measurements. It was shown that soil microaggregates are formed under the impact of a number of physicochemical processes; the content and properties of inorganic components (clay minerals in soils with a high CEC and iron oxides in soils with a low CEC) are the controlling factors. The structure of the parent materials is transformed to different degrees to form the soil structure. For example, autonomous nondifferentiated soils inherit, to some extent, the specific microorganization of the parent material. At the same time, the redistribution of substances in the soil profile and in the landscape may exert a substantial influence on the soil structure and microstructure. This is particularly true for autonomous differentiated soils, turbated soils, accumulative soils, polylithogenic soils, and polygenetic soils. The properties of the obtained subfractions of the clay (the mineralogical composition, the Fe2+/(Fe2+ + Fe3+) ratio, the magnetic susceptibility, and the Cha/Cfa ratio) attest to the spatial heterogeneity of the composition and properties of the mineral and organic aggregated compounds in soils.

<p>The transport of colloidal organic matter (OM) in soil is governed by colloidal hydrodynamics and frequently features strong interactions at the biogeochemical interfaces provided in the soil pore space. Conventional reactive tracers used to study solute transport usually fail to cover the hydrodynamics of small-sized colloidal OM. This impedes a clear observation of transport phenomena that are characteristic for these OM fractions. Tailor-made poly(ethylene glycol) (PEG) is available in a molar mass range featuring similar hydrodynamic sizes as colloidal OM. Thus, characterizing the transport of PEG could help to decipher the transport behavior of colloidal OM in soil.<br>We studied the transport of PEG in soil columns filled with homogenized Cambisol material. PEG was labelled with fluorophores to enable a highly resolved and sensitive detection via fluorescence spectroscopy. Parallel factor analysis (PARAFAC) was applied to the measured excitation-emission matrices to estimate the concentration of PEG in the column effluent. Additionally, batch experiments were conducted to determine the adsorption isotherms of PEG with the column substrate and typical soil minerals.<br>The resulting breakthrough of PEG was retarded by about an order of magnitude and with a pronounced tailing when compared to the breakthrough of non-reactive NaCl. The retardation points towards organo-mineral associations. This was corroborated by the adsorption observed in batch experiments with high maximum adsorption capacity with homogenized soil and clay minerals. The observed tailing may be due to the varying molecular dimensions of PEG contributing to kinetic interactions with soil minerals.<br>With representative hydrodynamics, varying molecular dimensions as colloidal OM and the possibility of forming organo-mineral associations with soil minerals, tailor-made PEGs are promising candidates to also follow the transport of other colloidal OM.</p>

Environmental Soil Chemistry

Rock-forming minerals of igneous and metamorphic rocks contain most of the nutrients required by higher plants for growth and development. Ground rock fertilisers may provide a source of nutrients to depleted topsoils where bulk soil solutions are not in equilibrium with fresh primary minerals. Slow dissolution rates of silicate minerals may inhibit the use of rock powders in agriculture unless suitable soils are identified and optimum rock powder properties developed. This review identifies previous research where the agronomic effectiveness of ground rock fertilisers has been evaluated. There are many contradictory findings that need to be evaluated by reference to basic geochemical knowledge. Geochemical studies of mineral dissolution indicate the general reaction pathways by which nutrients are released, assuming that equilibrium between the soil solution and primary mineral is achieved. In soils, mineral dissolution is enhanced by disequilibrium between soil solution and mineral surfaces through the removal of ions by processes such as leaching and nutrient uptake. Rhizosphere processes and other biological activity may further enhance mineral dissolution through the release of H-ions and complexing organic compounds which react with mineral surfaces. Geochemical principles can be used to predict some of the reactions that occur when ground silicate minerals are added to soils as mineral fertilisers. A range of weathering rates for minerals have been identified in the laboratory and the field and are dependent on physical, mineralogical and biogeochemical factors. The rate limiting steps may be those that involve reactions between the soil solution and mineral surface. Dissolution primarily occurs at defects at the mineral surfaces and an understanding of these surface reactions may lead to preparative procedures to enhance nutrient release from the mineral surface. Normalising the release rates of nutrients to a unit surface area basis can aid in predicting nutrient release during dissolution from various ground rock materials. Identifying the relationships between release rates of minerals and plant uptake is vital to developing an understanding the effectiveness of rock dust applied to vegetated soils.

Silicon isotopes record dissolution and re-precipitation of pedogenic clay minerals in a podzolic soil chronosequence

Potassium Nutrition of the Rice– Wheat Cropping System

Adsorption characteristics of cesium on the clay minerals: Structural change under wetting and drying condition

Adsorption of microorganisms on minerals is a ubiquitous interfacial phenomenon in soil. Knowledge of the extent and mechanisms of bacterial adsorption on minerals is of great agronomic and environmental importance. This study examined adsorption of Bacillus subtilis on three common minerals in soils such as kaolinite, montmorillonite and goethite under various environmental conditions. Isothermal titration calorimetry (ITC) was used to investigate the effects of temperature (20, 30, and 40°C), pH (5.0, 7.0, and 9.0) and KNO3 concentration (0.001, 0.01, and 0.1 mol L−1) on the adsorption by direct measurement of enthalpies. The results revealed that the adsorption process in all the mineral systems were exothermic, with the enthalpy changes (ΔHads ) ranging from −52 to −137, −33 to −147, and −53 to −141 kJ kg−1 (dry weight of adsorbed bacteria) for kaolinite, montmorillonite, and goethite, respectively. No obvious dependence of ΔHads on temperature was observed. The heat release for all the systems generally declined with pH and decrease of salt concentration, which can be explained by the variations of hydrophobicity and electrostatic force with pH or salt concentration. The largest decrease was found for goethite among the three minerals from pH 5.0 to 7.0, suggesting that electrostatic attraction may play a more important role in bacterial adsorption on this mineral. The ΔHads values for all the minerals became nearly the same at pH 9.0, indicating that the same force probably hydrophobicity governing the adsorption for the minerals in alkaline environment. It is assumed that acidic or saline soils and the associated environments favor the adsorption of B. subtilis on clay minerals. In addition, the negative enthalpies expressed as kJ kg−1 (carbon) revealed an energy flow into the environment accompanied by the carbon adsorption on the minerals in soil.

A brief review of world experience in mapping the mineralogical composition of soils is given; in particular, the results gained in Great Britain (England and Wales), Canada, the United States, Australia, Hungary, the former Soviet Union, and Russia are analyzed. In the majority of countries, the composition of clay minerals was the only object of mapping, except for the United States, for which the data on the mineral composition of coarse fractions were included. This publication is aimed at the analysis of the experience in mapping the mineralogical composition of soils in Moldova—a small country with steppe and forest-steppe landscapes—and elucidates the achievements and problems in this area. Unlike other countries, where the associations of clay mineral were the object of mapping, the specific mineralogical composition of soils and parent materials in Moldova, together with the development and application of appropriate analytical methods and databases, made it possible to compile the maps reflecting the contents of individual minerals both in the clay and coarse fractions. For the first time, digital maps of the contents of various minerals in soils of Moldova were developed on the basis of data of quantitative X-ray diffractometry and their statistical analysis. A close relationship was found between the content of certain minerals and the particle-size distribution data, which permitted us to perform mapping of the mineralogical composition of soils with due account for their textures. As an example, digital maps of the contents of clay minerals (smectite and illite) in the A horizon and in the parent material of Moldavian chernozems and forest soils on a scale of 1 : 3 M are presented. Statistical data on the contents of these minerals in the soils of different textures are discussed. The content of smectite varies within 6–43%, and the content of illite varies within 3–16%. Their distribution in the soil profiles attests to a statistically reliable difference between the contents of these minerals in the A horizon and in the parent material. The mapping procedure is described, and the areas of the practical application of such maps are specified.

<p>Long-term coal mining (more than 50 years) in the Moscow basin has a complex negative effect on soils. Because of underground mining at coal fields spoil heaps with a high content of iron sulfides, aluminosilicates and organic carbon of coal origin were formed. Oxidation of sulfides and acid hydrolysis of aluminosilicates in waste dumps results in the producing of toxic sulfuric acid, Al and Fe sulfates (Nordstrom and Alpers 1999). Acid mine drainage (AMD) entering from eroded spoil heaps, leads to physico-chemical and morphological changes in soil characteristics. On foreslopes around spoil heaps technogenically transformed soils are common. Our study aimed at evaluation of post-mining geochemical evolution of chemical composition and properties of solid and liquid soil phases.</p><p>We examined two key sites within abandoned coal mine fields in the central part of the Moscow basin. Predominant natural soils are Greyic Phaeozems and Haplic Chernozems (WRB 2014) (Grey forest and Leached Chernozems in Russian classification).</p><p>Soil samples and displaced soil solutions (by ethanol) were analysed for acid-base properties, content and composition of readily soluble salts, content of Fe<sup>2+</sup> and Fe<sup>3+</sup>, H<sup>+</sup> and Al<sup>3+</sup>, composition of exchangeable cations, heavy metals (HM) and organic carbon) by standard methods. The composition of clay minerals in soils were determined by X-ray diffractometry. The saturation degree of soil solutions by gypsum, iron and aluminum hydroxides was estimated.</p><p>Properties of technogenic soils differ significantly from natural soils. We observed the transformation of the composition of soil solutions. Key geochemical processes at mine sites in contaminated soils were: (1) acidification and Fe-Al-SO<sub>4</sub> salinization of entire soil profile along with the increment in H<sup>+</sup> and Al<sup>3+</sup> ions content; (2) cation exchange, leading to displacement of Cа<sup>2+</sup> and Mg<sup>2+</sup> ions by Al<sup>3+</sup>, H<sup>+</sup> and, probably, by Fe<sup>2+</sup> and Fe<sup>3+</sup> in soil cation-exchange complex (CEC); (3) alteration of radial differentiation of organic carbon and carbonates in soils; (4) clay mineral transformations.</p><p>Topsoil features a high content of technogenic organic carbon (reaches 12%) due to the inflow of coal material particles from the dump. Ca<sup>2+</sup> and Mg<sup>2+</sup> ions predominate (for 70 to 90%) in CEC of natural soils. Exchangeable Al<sup>3+</sup> accounts for more than 75% of the acidity formation in transformed soils. The share of exchangeable Ca<sup>2+ </sup>and Mg<sup>2+</sup> in CEC of contaminated soils depletes on 22-38%.</p><p>Extracted soil solutions from polluted soils are heavily oversaturated by Al hydroxides. Even though the activity of Ca<sup>2+</sup> and SO<sub>4</sub><sup>2-</sup> ions in some samples reaches the gypsum saturation level, gypsum neoformations are not distinguished morphologically.</p><p>The content of Co, Сu, Ni and Zn in displaced solutions of transformed soils in tens or even hundreds times exceeds the background values. The clay minerals of natural soils are represented by kaolinite, illite, vermiculite and mixed-layer minerals. The sharp increase in smectite fraction (up to 75-80%) and slightly in chlorite fraction was revealed in transformed soils.</p><p>Post-technogenic soils have no analogues in natural forest-steppe landscapes of the Russian Plain.</p><p> </p>

Four soils with sandy/loamy boundaries occurring at various depths were studied with respect to distribution of clay‐sized minerals within the soil matrix. Mineralogy of coarse and fine clay was determined by horizon using x‐ray diffraction. Also, mineralogy of clay from ped interiors vs. exteriors (coatings) was determined for the Bt horizon of one soil. Mineralogical differences in coarse‐clay distribution were observed with respect to location above or below the sandy/loamy boundary. Clay above the boundary was consistently high in hydroxy‐interlayered vermiculite (HIV) and quartz, regardless of depth to the boundary. One exception was the A horizon of a Spodosol, which consisted essentially of quartz; however, the Bh horizon of this soil (above the boundary) did contain appreciable HIV. Below the boundary, the upper Bt horizon exhibited an increase in kaolinite and a sharp decrease in quartz relative to overlying E or Bh horizons. A marked decrease in HIV below the upper Bt horizon was also evident. Fine clay contained more kaolinite and less HIV and quartz than did coarse clay, and exhibited less intra‐pedon variation. Possibly HIV comprises a greater proportion of the clay residue in eluvial horizons because of the greater size of its precursor, which could be mica, and subsequent resistance to translocation. The greater abundance of HIV in ped coatings relative to ped interiors suggests that some contemporary translocation of coarser clay from HIV‐dominated eluvial horizons has occurred along major voids between peds. The d 001 peak shift with heat treatment for HIV was similar for all samples, suggesting that depth and landscape position have had little influence on degree of interlayer polymerization in these soils.

PurposeThe close association of Fe-oxyhydroxides and clay minerals might influence the sorption properties of these components. We aimed to study the effect of removing the pedogenic Fe-oxyhydroxides on the sorption of Cd, Cu, Pb, and Zn by the clay mineral particles in soils with contrasting pH.MethodsCompetitive batch sorption experiments before and after Fe-oxyhydroxide extraction in soils were carried out together with the direct analysis of the metal sorption on individual particles of ferrihydrite, smectite, and illite/smectite by TEM.ResultsFerrihydrite was a more effective metal sorbent than clay minerals, although its removal resulted in decreased sorption only for Cd, Cu, and Zn. Ferrhydrite coating blocked metals’ access for certain sorption sites on clay surfaces, which were only accessible for Pb as the most efficient competitor after removing the coating. This observation was the most remarkable for the smectite particles in the alkaline soil. Mineral surfaces sorbed higher Cu than Pb concentrations and higher Zn than Cd concentrations despite the former metals’ lower bulk sorption. Thus, organic surfaces and precipitation contributed to Pb and Cd’s retention to a greater extent than for Cu and Zn. The structural Fe of smectite also promoted the metal sorption in both soils.ConclusionRemoval of iron-oxyhydroxide coatings from the soil affects metal sorption selectively. Direct study of metal sorption on individual soil particles enables us to gain a more in-depth insight into soil minerals’ role in this process.

Techmer PM launches new anti-slip additive

The interaction between soil minerals and soil organic matter (SOM) plays an important role in governing carbon release and sequestration in soil, yet understanding their behavior during wildfires remains poorly understood. This study examined the evolution of humic acid (HA, a representative of SOM) under simulated wildfire heating conditions (30-900 °C) in the presence of two representative soil minerals: montmorillonite (Mnt) and ferrihydrite (Fhy). Whereas Fhy accelerated the mineralization of HA, Mnt enhanced its preservation. These disparities stemmed from variations in the surface reactivity, structure, and transformations of Fhy and Mnt. Lewis acid sites, more abundant on Fhy surfaces than on Mnt surfaces, enhanced the decarboxylation of HA and caused carbon losses as CO2. However, Brønsted acid sites, which are more abundant on Mnt surfaces than on Fhy surfaces, enhanced carbon preservation by promoting HA isomerization and aromatization. Above 350 °C, lattice oxygen release from Fhy promoted the oxidative decomposition of HA, while Fhy itself underwent reduction to form magnetite, wüstite, and zero-valent iron. The confinement of HA within the micro/mesopores created by Mnt's inert nanolayers prevented the thermal degradation of HA, enhancing carbon preservation. These findings advance our understanding of the specific roles of soil minerals in the decomposition, transformation, and preservation of SOM during wildfires.