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Clay delving in strongly texture-contrast soils brings up subsoil clay in clumps ranging from large clods to tiny aggregates depending on the equipment used and the extent of secondary cultivation. Clay delving usually increases crop yields but not universally; this has generated questions about best management practices. It was postulated that the size distribution of the subsoil clumps created by delving might influence soil-water availability (and hence crop yield) because, although the clay increases water retention in the root-zone, it can also cause poor soil aeration, high soil strength and greatly reduced hydraulic conductivity. We prepared laboratory mixtures of sand and clay-rich subsoil in amounts considered practical (10% and 20% by weight) and excessive (40% and 60% by weight) with different subsoil clod sizes ( Additional keywords: aggregate size distribution, soil physical limitation, sandy soils, tillage. Received 22 April 2015, accepted 18 July 2015, published online 11 April 2016, Introduction Texture-contrast soils (Isbell 2002) dominate a significant proportion of the cropping lands in the Mediterranean parts of southern Australian and present a peculiar set of soil physical and chemical [...]

Abstract: Defining soil clay minerals as all inorganic particles < 2 µm would enhance their predictive power for soil functions. The future task is to unravel the prominent functional role of clay associations in the “ultimate particles” in soils–microaggregates. High energy techniques and decomposition of XRD patterns offer the prospect of understanding associations of silicates, oxides and organic matter within microaggregates. [ABSTRACT FROM AUTHOR]

Microbially mediated smectite illitization has been extensively demonstrated in laboratory experiments. Despite occasional observations in geological environments, the transformation mechanism is still poorly understood. Here we investigated a series of volcanic ash (tephra) samples from the Permo-Triassic boundary (PTB) successions of South China, using short-wavelength infrared (SWIR) spectroscopy, in combination with XRD, MIR, EPMA, SEM, TEM, and 27 Al NMR analyses, in order to establish a better understanding of microbial illitization, and to test the applicability of SWIR as a monitor for this process. Mixed-layer illite-smectite (I-Sm) clays are the predominant clay minerals, with illite percentages ranging from 32 to 93%. The (060) value of I-Sm varies from 1.4956 to 1.4996 Å, indicating a dioctahedral precursor smectite. The precursor smectite of I-Sm is nearly free of Fe, and is probably montmorillonite. The b -cell dimension ( b 0 parameter) exhibits a positive correlation with the illite percentage of I-Sm, suggesting that the illitization occurs with significant cation substitutions. The different spectroscopic results all indicate that tetrahedral Al substitutes for Si, and octahedral Al is mainly substituted by Mg and/or Fe with illitization, consistent with the findings of XRD analysis. Chemical compositions and trends in their variation show typical features of a dissolution-precipitation (DP) mechanism. The SEM images reveal abrupt changes in morphology and the TEM analyses suggest progressive changes in polytype with illitization, also supporting the DP process. The transformation mechanism of I-Sm contradicts the conventional wisdom concerning diagenetic bentonite I-Sm, similar to that of hydrothermal origin, probably as the result of to the involvement of microorganisms. The SWIR parameters, such as position, depth, area and asymmetry of the absorption bands, versus illite percentage in I-Sm, generally give good correlations. SWIR spectroscopy is demonstrated as a valuable method to identify I-Sm with different percentages of illite, and with a capability as a sensitive monitor for I-Sm structure ordering and crystal-chemistry. Thus it can be used as an alternative or complementary method in conventional I-Sm studies, as well as in epithermal and hydrocarbon-reservoir explorations and astrobiological investigations. [ABSTRACT FROM AUTHOR]

The Mg-rich clay minerals, palygorskite, sepiolite and also Mg-smectites are generally rare in soils. When they occur they are usually concentrated in subsurface horizons and become replaced by other minerals, e.g., dioctahedral smectites in near-surface horizons. Salt-affected soils on limestone in a flat landscape in southern Australia showed patchy pasture growth, including areas in which almost no growth occurred. Chemical and mineralogical analyses of deep profiles of the soils revealed two main types and that the extent of plant growth reflected their mineralogical composition. The soil type in which plants grow well (‘Chromosol’, an Alfisol) contains dioctahedral smectite (montmorillonite and/or beidellite) but only in substantial amounts at depth. The soil type in which little or no plants grew (‘Vertosol’, a Vertisol) has substantial concentrations of a trioctahedral Mg-smectite, saponite, in its surface horizons along with dioctahedral smectite in lower horizons. Both soil types contain sepiolite and palygorskite, largely in the lower horizons of the Chromosol, but also in near-surface horizons of the Vertosol. Both types of soil also contain illite and kaolinite, which are each concentrated in the upper horizons of the soils and are considered to be detrital. The genesis of the two main types of soils can be explained by the depositional history of the basin. On the eastern side of the basin, palustrine limestone formed when the sediments became exposed, possibly from uplift. The Chromosol formed on this material. On the western side, by contrast, lacustrine sediments on lowland adjacent to a stranded beach ridge, experienced prolonged seasonal inundation by water leading to the formation of the Vertosol. This soil is strongly sodic and strongly alkaline throughout and it is concluded that the high concentration of saponite in the surface swells and thereby ensures that the soil remains wet. Together with its high pH, this soil has very poor conditions for plant growth. The persistence of the Mg-rich clay minerals, especially saponite, at the surface of the Vertosol, suggests that the relative lack of plants has preserved these minerals throughout the profile. [ABSTRACT FROM AUTHOR]

New insights from the recent literature are summarized and new data presented concerning the formation, structure and morphology of halloysite. Halloysite formation by weathering always requires the presence of water. Where substantial drying occurs, kaolinite is formed instead. Halloysite formation is favoured by a low pH. The octahedral sheet is positively charged at pH < ∼8, whereas the tetrahedral sheet is negatively charged at pH > ∼2. The opposing sheet charge would facilitate interlayer uptake of H2O molecules. When halloysite intercalates certain polar organic molecules, additional (hkl) reflections appear in the X-ray diffraction pattern, suggesting layer re-arrangement which, however, is dissimilar to that in kaolinite. Associated oxides and oxyhydroxides of Fe and Mn may limit the growth of halloysite particles as does incorporation of Fe into the structure. Particles of different shape and Fe content may occur within a given sample of halloysite. [ABSTRACT FROM AUTHOR]

Tubular halloysite has many applications as a nanomaterial. Spheroidal halloysite (SPH) is the other most common form of halloysite. Its mode of formation has had different explanations, including association with allophane, or more generally, following weathering of volcanic glass. Some SPHs have formed from minerals in crystalline rocks, sometimes as an early stage of evolution into plates and/or tubes of halloysite and ultimately to kaolinite. Spheroidal halloysites can show a range of Fe contents and can occur with other forms of halloysite; they have often formed in confined environments whereas tubular halloysites apparently form in more open spaces. They have also formed on microbes or where there is a significant amount of organic matter. Generally, SPHs have often formed by rapid dissolution of volcanic glass and primary minerals. The SPHs can persist over time. They have few active edges, so interparticle interaction is poor, causing low viscosities in clay-water suspensions, poor soil stability and low adsorption capacities. [ABSTRACT FROM AUTHOR]

The Mg-rich clay minerals, palygorskite, sepiolite and also Mg-smectites are generally rare in soils. When they occur they are usually concentrated in subsurface horizons and become replaced by other minerals, e.g., dioctahedral smectites in near-surface horizons. Salt-affected soils on limestone in a flat landscape in southern Australia showed patchy pasture growth, including areas in which almost no growth occurred. Chemical and mineralogical analyses of deep profiles of the soils revealed two main types and that the extent of plant growth reflected their mineralogical composition. The soil type in which plants grow well (‘Chromosol’, an Alfisol) contains dioctahedral smectite (montmorillonite and/or beidellite) but only in substantial amounts at depth. The soil type in which little or no plants grew (‘Vertosol’, a Vertisol) has substantial concentrations of a trioctahedral Mg-smectite, saponite, in its surface horizons along with dioctahedral smectite in lower horizons. Both soil types contain sepiolite and palygorskite, largely in the lower horizons of the Chromosol, but also in near-surface horizons of the Vertosol. Both types of soil also contain illite and kaolinite, which are each concentrated in the upper horizons of the soils and are considered to be detrital. The genesis of the two main types of soils can be explained by the depositional history of the basin. On the eastern side of the basin, palustrine limestone formed when the sediments became exposed, possibly from uplift. The Chromosol formed on this material. On the western side, by contrast, lacustrine sediments on lowland adjacent to a stranded beach ridge, experienced prolonged seasonal inundation by water leading to the formation of the Vertosol. This soil is strongly sodic and strongly alkaline throughout and it is concluded that the high concentration of saponite in the surface swells and thereby ensures that the soil remains wet. Together with its high pH, this soil has very poor conditions for plant growth. The persistence of the Mg-rich clay minerals, especially saponite, at the surface of the Vertosol, suggests that the relative lack of plants has preserved these minerals throughout the profile. [ABSTRACT FROM AUTHOR]

ABSTRACT Palaeoenvironmental DNA (PalEnDNA) is defined as ancient DNA (aDNA) originating from disseminated genetic material within palaeoenvironmental samples. Sources of PalEnDNA include marine and lake sediments, peat, loess, till, ice, permafrost, palaeosols, coprolites, preserved gut contents, dental calculus, tephras, and soils as well as deposits in caves/rockshelters and at archaeological sites. PalEnDNA analysis provides a relatively new tool for Quaternary and archaeological sciences and its applications have included palaeoenvironmental and palaeodietary reconstructions, testing hypotheses regarding megafaunal extinctions, human-environment interactions, taxonomic studies, and studies of DNA damage. Because PalEnDNA samples comprise markedly different materials, and represent wide-ranging depositional and taphonomic contexts, various issues must be addressed to achieve robust, reproducible findings. Such issues include climatic and temporal limitations, the biological origin and state (free versus bound) of PalEnDNA, stratigraphic reliability, sterile sampling, ability to distinguish modern from aDNA signals, DNA damage and PCR amplification, DNA extraction methods, and taxonomic resolution. In this review, we provide a non-specialist introduction to the use of PalEnDNA for Quaternary and archaeological researchers, assess attributes and limitations of this palaeoenvironmental tool, and discuss future prospects of using PalEnDNA to reconstruct past environments. [ABSTRACT FROM AUTHOR]

Four different cationic polymers that varied in chemical type, cation density and molecular weight were reacted with a Wyoming bentonite (<2 μm fraction) over a wide range of polymer/clay ratios. Each of the polycations [a poly-diallyldimethylammonium chloride (poly-DADMAC), a polyamine, a polystyrene and a polyacrylamide] is a quaternary ammonium derivative of a polymer. The polyacrylamide actually comprises a copolymer of polyacrylamide. Carbon content, basal spacing by X-ray diffraction (XRD), elemental composition by X-ray fluorescence and zeta potential were measured for each of the polymer–clay complexes. The various polymer–clay complexes were studied for their capacities to remove toluene from water, and for the stabilities of sorbed toluene. All of the polycations reacted to form interlayer complexes with the clay, although the clay association with a low-charge density polyacrylamide was weak. Except for the polyacrylamide, which displaced little Na+ and no Ca2+, polycations displaced most exchangeable Na+ from the clay at low loadings (<0.25 g polymer g−1 clay), but only displaced most of the exchangeable Ca2+ at quite high loadings (up to 2 g polymer g−1 clay). Clay–polymer reactions were largely completed at quite low polymer/clay ratios, although the poly-diallyldimethylammonium chloride (poly-DADMAC) reacted, at a reduced efficiency, at loadings up to 4 g polymer g−1 clay. Only the poly-DADMAC showed distinct high-spacing XRD peaks for multilayer intercalation of polymer by the clay. Clay–polymer complexes formed with the polystyrene polycation were the most effective for removing toluene from solution. Clay–polystyrene complexes had a similar uptake of toluene and their association with toluene is of similar stability as complexes of the clay with a double-chain alkyl ammonium cation. Where it occurred, uptake of toluene by clay–polymer complexes reached a maximum at quite low loadings of polymer (∼0.5 g g−1 clay). Uptake was maintained at or near the maximum level when polymer loadings increased to quite high values. This suggests direct interaction of the toluene with the polycation on the clay rather than its uptake into spaces between polymer pillars. Complexes involving the polyamine, poly-DADMAC and polystyrene, but not the polyacrylamide, all developed a positive zeta potential at high loadings of polymer. Except for the polyacrylamide complexes, zeta potentials steadily became less negative as polymer content in complexes increased from zero, indicating some polycations occupying external surfaces as well as interlayers. However, charge reversals only took place at high loadings of polymers, when the amounts of polycations sorbed were close to that required to satisfy the clay cation exchange capacity. [Copyright &y& Elsevier]

This study provides fundamental knowledge about the interaction of allophane, deoxyribonucleic acid (DNA), and organic matter in soils, and how allophane sequesters DNA. The adsorption capacities of salmon-sperm DNA on pure synthetic allophane (characterised morphologically and chemically) and on humic-acid-rich synthetic allophane were determined, and the resultant DNA–allophane complexes were characterised using synchrotron-radiation-derived P X-ray absorption near-edge fine structure (XANES) spectroscopy and infrared (IR) spectroscopy. The synthetic allophane adsorbed up to 34 μg mg − 1 of salmon-sperm DNA. However, the presence of humic acid significantly lowered the DNA uptake on the synthetic allophane to 3.5 μg mg − 1 by occupying the active sites on allophane so that DNA was repulsed. Both allophane and humic acid adsorbed DNA chemically through its phosphate groups. IR spectra for the allophane–DNA complex showed a chemical change of the Si–O–Al stretching of allophane after DNA adsorption, possibly because of the alteration of the steric distance of the allophane outer wall, or because of the precipitation of aluminium phosphate on allophane after DNA adsorption on it, or both. The aluminol groups of synthetic allophane almost completely reacted with additions of small amounts of DNA (~ 2–6 μg mg − 1 ), but the chemical adsorption of DNA on allophane simultaneously led to the formation of very porous allophane aggregates up to ~ 500 μm in diameter. The formation of the allophane nano- and microaggregates enabled up to 28 μg mg − 1 of DNA to be adsorbed (~ 80% of total) within spaces (pores) between allophane spherules and allophane nanoaggregates (as “physical adsorption”), giving a total of 34 μg mg − 1 of DNA adsorbed by the allophane. The stability of the allophane–DNA nano- and microaggregates likely prevents encapsulated DNA from exposure to oxidants, and DNA within small pores between allophane spherules and nanoaggregates may not be accessible to enzymes or microbes, hence enabling DNA protection and preservation in such materials. By implication, substantial organic carbon is therefore likely to be sequestered and protected in allophanic soils (Andisols) in the same way as demonstrated here for DNA, that is, predominantly by encapsulation within a tortuous network of nanopores and submicropores amidst stable nanoaggregates and microaggregates, rather than by chemisorption alone. [ABSTRACT FROM AUTHOR]