Quantity/intensity and quantity/potential studies in Na–Ca exchange system in some salt-affected soils

The Q/I curves for Na in the Na–Ca system in some salt-affected soils of Malaprabha and Ghataprabha river valleys lacked the curvature commonly seen in the Q/I curve for potassium. The Malaprabha soils showed lower AR₀^Na , Na_L and BC₀^Na values and higher energies of replacement of calcium by sodium than the Ghataprabha soils; the latter showed a higher affinity for Na than Ca. Two distinct linear parts of the quantity/ potential curves, with different slopes, indicated that Na is held in these soils in two characteristic types of exchange sites having different affinities for sodium. The intersection of the two linear parts corresponded to ESP values in the range of 13 to 64%. The change in the affinity at such a high degree of Na saturation was attributed to the presence of chloritized smectitic clays and sodium-selective zeolite, such as analcite, reported in these soils.     

Effect of ionic strength on the cation exchange capacity of some forest soils

Abstract

Cation exchange capacity (CEC) of the 0–5 cm depth of forest soils increased with the square root of solution ionic strength over the experimental range of 6 to 96 mM. Percentage increases in CEC were positively correlated with percentage organic carbon; for mixed hardwood forest soils, increases were 38% for soils with 3.3% carbon, and 105% for soils with 7.4% carbon when ionic strength was varied over the full experimental range. When analyzing soils with constant‐potential surfaces, both pH and ionic strength must be controlled, preferably at or near levels found in the field, in order to provide interpretable measures of CEC.     

Pb/Ca ion exchange on kaolinite clay modified with phosphates

Purpose  

Pollution of soils by heavy metal ions has attracted global concern because of the subsequent translocation into food chain which when taken up to a certain level can cause serious health problems. The influence of preadsorbed calcium by kaolinite clay modified with orthophosphate and tripolyphosphate reagents on the mobility of Pb²⁺ in kaolinitic soil system is studied. This is with the view to understand the fate of Pb²⁺ in phosphate-fertilized kaolinitic soils that are subsequently limed.     

Quantity-intensity relationship for characterizing ammonium chemistry of Bangladesh soils in reference to clay mineralogy

Ammonium chemistry in surface soils collected from major soil series of Bangladesh was studied in terms of quantity-intensity (Q/I) relationship. Soils were classified according to physiography and parent materials; calcareous floodplain soils were dominated by mica and smectite, while non calcareous floodplain soils, terrace soils, and hill soils were dominated by mica or kaolinite and lacked smectite as a major clay mineral. Different Q/I parameters were obtained between soils of smectitic and non-smectitic types. Soils of smectitic type had a high potential buffering capacity which kept the equilibrium activity ratio at a low and fixed level.. The content of labile ammonium was high and estimated to increase with increasing addition of NH₄ ⁺. In contrast, soils of non-smectitic type with a low potential buffering capacity showed a considerable variation of both the equilibrium activity ratio and labile ammonium content, as affected by the application of NH₄ ⁺. Based on the ammonium chemistry, expected N-fertilizer application was compared with the prevailing application method.     

Effect of clay content and silt—clay fabric on stability of artificial aggregates

The influence of clay content and silt–clay fabric on aggregate stability was investigated. Two silt—clay fabrics were produced in the laboratory by mixing silt particles with a clay phase: (i) a loose packing of the silt particles with clay aggregates, and (ii) a close packing of the silt particles with the dispersed clay phase, the latter coating and bridging the silt particles. Porosity and pore size distribution were measured, and the silt—clay fabric was described using scanning electron microscopy. The aggregate stability was measured under three treatments corresponding to different wetting conditions and energy levels: fast wetting, mechanical breakdown and slow wetting. Our results show that aggregate stability is related to both clay content and silt—clay fabric. Comparison of fragment size distributions and their mean weight diameter amongst the three treatments enabled identification of mechanisms responsible for the variation of aggregate breakdown. The compression of trapped air was the predominant breakdown mechanism for both fast and slow wetting and was related mainly to porosity characteristics. For the mechanical breakdown, the degree of disintegration depended on the cohesion of the silt–clay fabric, which is related to the continuity of the solid phase.     

Depositional seals in polyacrylamide-amended soils of varying clay mineralogy and texture

Purpose  

Depositional seals, formed when turbid waters infiltrate into soils, lead to a reduction in soil hydraulic conductivity (HC) and enhance runoff and soil erosion. Since clay size particles constitute a dominant proportion of depositional seals, soil texture and clay mineralogy play a significant role in determining the seal’s hydraulic characteristics. Presence of high molecular weight anionic polyacrylamide (PAM) in suspension flocculates fine sediments, and therefore, its application to the soil surface may modify the characteristics of the depositional seal. The impact of PAM on the latter is expected to be influenced by soil properties. The aim of this study was to elucidate the effects of PAM application on clay flocculation and the HC of depositional seals formed in four soils varying in texture (ranging from loamy sand to clay loam), and diverse proportions of clay mineral constituents (kaolinite, smectite, and vermiculite).     

Influence of clay mineralogy on the stability of a landslide in Plio-Pleistocene clay sediments near Grassano (Southern Italy)

Clayey silts involved in a landslide have been sampled to study the role of sediment composition in developing sliding surfaces. Five drillings enabled the collection of 46 samples and to define active slide surfaces and non-active surfaces (discontinuities).     

Thermodynamics of K-Ni and Ca-Ni exchange reactions on kaolinite clay

Exchange equilibria involving nickel ions on potassium and calcium kaolinites were studied using exchange isotherms and derived thermodynamic parameters. The equilibrium was attained within 3 h and maximum adsorption occurred at pH 5.5. The exchange at pH 5.5 and an equilibrium time of 3 h yielded isotherms, equilibrium constants and standard fne energy values indicating a higher preference for nickel ions on the kaolinite surface. A stronger binding of nickel ions on the kaolinite surface was suggested by the enthalpy changes and the entropy changes indicate an increase in order of the system which may be due to changes in hydration states of nickel, potassium and calcium ions. The surface-phase activity coefficients of the cations showed that with increasing nickel saturation, in the Ca-Ni system f_Ni continuously increased while f_Ca decreased; in the K-Ni system f_K first increased and then decreased while f_Ni first decreased and then increasad, which may be attributed to differences in the distribution of ions in the Gouy-Stem layer. The excess thermodynamic functions showed that the exchange reactions were non-ideal: that is the mixture of cations oh the kaolinite surface was more stable and more tightly bound than the homo-ionic forms.     

Thermodynamics of ammonium-calcium exchange on a halloysitic soil clay

Abstract

Prediction of the ionic composition of a soil solution which is at equilibrium with an exchanger phase is one of the main problems in soil chemistry. To date the most practical way to achieve this objective is to adopt a thermodynamic approach for the study of soil-solution systems. As of 1979 more than 300 sets of data on cation exchange on various clay minerals and soils had been subjected to thermodynamic analysis (Bruggenwert and Kamphorst 1979).     

Effect of the ionic strength of pulsed electric field treatment medium on the physicochemical and structural characteristics of lactoferrin

Pulsed electric field (PEF) treatment (35 kV cm(-1) for 19.2 μs using bipolar 2 μs pulses) was conducted on bovine lactoferrin (LF; 0.4 mg mL(-1)) prepared in simulated milk ultrafiltrate (SMUF), at concentrations between 0.2× and 2× normal strength, with electrical conductivities ranging from 0.17 to 1.04 S m(-1). The physicochemical and structural characteristics (LF content by a spectrophotometric and an ELISA method, surface hydrophobicity, electrophoretic mobility, far-UV circular dichroism spectra, and tryptophan fluorescence) of LF dissolved in SMUF of all strengths tested were not changed after PEF treatment. The PEF treatment of LF in 0.2 strength SMUF did not cause the release of LF-bound ferric ion into the aqueous phase, with a concentration of LF-bound iron being the same as that of the untreated LF control (174 μg L(-1)). However, in treatment media with higher ionic strengths, ferric ion was released from the LF molecule into the aqueous phase. The concentration of LF-bound iron decreased from 174 μg L(-1) for the LF treated in 0.2 strength SMUF to 80 μg L(-1) for that treated in double-strength SMUF. The results suggest that the PEF-induced iron depletion of LF does not appear to cause an appreciable conformational change in LF molecules. PEF treatment could be developed as a novel physical way to produce iron-depleted LF, as an alternative to the existing chemical method.     

Effect of pH on the rheological and structural properties of gels of water-washed chicken-breast muscle at physiological ionic strength

Adjustment of pH from 6.4 to neutrality improved gelling ability and water-holding capacity of twice water-washed, minced chicken-breast muscle significantly at physiological ionic strength, at which the majority of the myofibrillar proteins, including myosin, are not soluble. A strain value of 2.2 was obtained at neutral pH. Myofibrils were the main components of the gel network at both pH 6.4 and 7.0; however, the myofibrillar distribution varied with the pH value. At pH 6.4, myofibrils formed a network of localized aggregates leaving large voids between, whereas at neutral pH, an evenly distributed network of myofibrils was formed. In addition, at neutral pH, a network of fine strands was found within the network of myofibrils. The network was much less developed at pH 6.4. The thin and thick filaments within each myofibrillar structure were disorganized at both pH values. The intramyofibrillar spaces were larger at neutral pH than at pH 6.4. It was proposed that adjustment of pH to neutrality increased electrostatic repulsion leading to a more even distribution of the myofibrillar proteins, a key factor responsible for the improved gel strength and water-holding capacity.     

Implications of clay mineralogy to the weathering and chemistry of AP horizons of ando soils in Japan

The clay mineralogy of 22 samples of the Ap horizons of Ando soils was determined by a combination of methods. Of these samples, 15 did and 7 did not contain allophane and imogolite. Opaline silica was found in 4 samples, whereas aluminum—humus complexes, iron oxides and layer silicates were found in all samples. The presence of allophane and imogolite and the absence of opaline silica in a few Ap horizons was related to mixing of A₁ horizons and subsoils by cultivation and to lower supplies of organic matter relative to the amounts of aluminum released from volcanic ash by weathering. The contents of 2:1 and 2:1:1 layer silicates and their intergrades were larger in soils in which quartz predominated in fine fractions. It was inferred that aluminum bound with humus and in allophane-like constituents, rather than aluminum in allophane and imogolite, is important in reactions with phosphate and fluoride.     

Effects of season and management on the vane shear strength of a clay topsoil

Vane shear strength, water status and bulk density were measured at various times in a growing season at two depths in a swelling clay topsoil. The site comprised experimental plots that had been ploughed annually, or direct-drilled for 10 years; short-term fallow areas, created on adjacent long-term grassland, were compared with the arable plots. In the middle of the topsoil layer (nominally 120 mm depth) of all three treatments shear strength was linearly related to water content, and similarly to bulk density in the direct-drilled and ploughed soils. Closer to the soil surface (nominally 40 mm), relationships between strength and wetness or density were less distinct, particularly in the spring, when drying was not accompanied by an increase in strength; possible reasons for this anomaly are considered. The shear strength of the untilled soils was greater, at both depths, than that of the ploughed soil. Other factors including density, water potential, soil structure and organic constituents, differed with time or between treatments, and their contribution to variations in shear strength are discussed.     

Potential role of soil density and clay mineralogy in assessing the suitability of soils for mole drainage

The failure mechanisms causing mole channel deterioration or collapse, which are controlled mainly by the shear, swell/shrink and apparent viscosity properties of soils, are shown to be sensitive to the influence of soil density and clay mineralogy. These two properties have, therefore, a clear potential role in helping to assess the suitability of soils for mole drainage and in helping to define the particular failure mechanisms which are most likely to be active in given situations.     

The influence of clay mineralogy and diagenesis of Upper Carboniferous shales on soil formation in parts of Devon

There is a correlation between variations in the clay mineral assemblages of the Crackington Formation (Upper Carboniferous) shales in parts of Devon, and the soil series mapped in the same areas. The differences in soil-forming characteristics of the shales are not due to mineralogy alone, but to various states of diagenetic induration which they have achieved. Brown earths (Dunsford series) are formed on steeper slopes of more durable, illite-chlorite dominated shales, whereas clayey soils (Tedburn and Halstow series) are typical of flatter, more poorly drained slopes of weaker illite and illite-kaolinite clay mineral assemblages. This result adds the geological component to earlier views that the different soil series are simply a consequence of physiographic and hydrologic position.     

Potassium status and clay mineralogy in ordinary chernozems treated with different rates of potassium fertilizers

The effect of a single instance of potassium fertilization at rates of 0, 70, 140, and 280 kg/ha on the potassium status and clay mineralogy was studied in a field experiment on ordinary chernozems. The content of exchangeable potassium determined by the Maslova method and the potassium potential vary with greatest reliability in response to increasing fertilizer rates. The content of easily exchangeable potassium and the potassium-buffering capacity are insignificantly affected by the application rate of potassium fertilizers. The chernozems under study without fertilization are characterized by a low supply of available potassium. When potassium fertilizers are applied at rates of 70 and 140 kg/ha, the soils pass into the category of unstable or high supply according to different gradation systems. The lower limit of the high or optimal supply category is reached only at the application of 280 kg/ha of potassium fertilizer. However, even in this case, chernozems are characterized by a low potassium supply according to the value of potassium potential and the content of nonexchangeable potassium. A single application of potassium fertilizers does not cause significant changes in the contents of illites in the clay fraction.     

Advances in characterization of soil clay mineralogy using X‐ray diffraction: from decomposition to profile fitting

Structural characterization of soil clay minerals often remains limited despite their key influence on soil properties. In soils, complex clay parageneses result from the coexistence of clay species with contrasting particle sizes and crystal chemistry and from the profusion of mixed layers with variable compositions. The present study aimed to characterize the mineralogy and crystal chemistry of the <2 μm fraction along a profile typical of soils from Western Europe and North America (Neo Luvisol). X‐ray diffraction (XRD) patterns were interpreted using: (i) the combination of XRD pattern decomposition and indirect identification from peak positions commonly applied in soil science; and (ii) the multi‐specimen method. This latter approach implies direct XRD profile fitting and has recently led to significant improvements in the structural characterization of clay minerals in diagenetic and hydrothermal environments. In contrast to the usual approach, the multi‐specimen method allowed the complete structural characterization of complex clay parageneses encountered in soils together with the quantitative analysis of their mineralogy. Throughout the profile, the clay paragenesis of the studied Neo Luvisol systematically includes discrete smectite, illite and kaolinite in addition to randomly interstratified illite‐smectite and chlorite‐smectite. Structural characteristics of the different clay minerals, including the composition of mixed layers, did not vary significantly with depth and are thus indicative of the parent material. The relative proportion of the <2 μm fraction increased with increasing depth simultaneously with smectite relative proportion. These results are consistent with the leaching process described for Luvisols in the literature.