Soil Clay Particles Research Articles

An analysis of soil fractal dimension in a sloping hedgerow agroforestry system in the Three Gorges Reservoir Area, China

Hedgerow intercropping provides an efficient method of controlling soil erosion and improving soil fertility on sloping agricultural land. Topsoil (0–20 cm soil layer) of 32 plots established in the Three Gorges Reservoir Area of the Yangtze River was sampled from the steep land between hedgerows (P1) and within hedgerows uphill (P2), under (P3) and downhill (P4) from the hedgerow were analyzed and the soil volumetric fractal dimension (DV) was calculated and the relationships between DV and soil physicochemical properties were tested. Results show that hedgerows effectively intercept clay particles in soil; the soil clay concentration within hedgerows was significantly higher (P < 0.05) than that of the soil between hedgerows at P1, respectively. The soil DV varied significantly among different positions in hedgerow systems, the DV of soil within hedgerows at P2, P3 and P4 were significantly higher (P < 0.05) than that of the soil between hedgerows at P1. DV was correlated positively and very significantly (P < 0.01) with the soil clay concentration (R 2 = 0.93) and silt content (R 2 = 0.74), and the DV was significantly (P < 0.01) and negatively correlated with soil sand content (R 2 = 0.78). The DV was significantly correlated with various soil physical properties and concentrations of soil nutrients. Therefore, the DV can be considered as a potential and accurate evaluating indicator for soil quality and nutrient conservation as they relate to the hedgerow intercropping on steep land.

Effects of Soil Organic Matter on Sorption of Metal Ions on Soil Clay Particles

Wien effect measurements were used to study the effect of organic matter on the interactions between divalent cations and soil clay particles of two black soil samples containing organic matter (OM) at 54.4 and 12.3 g kg−1 in the top (0–20‐cm) and bottom (100–120‐cm) horizons, respectively, and a sample of OM‐free black soil, all saturated with Cd2+, Cu2+, Pb2+, and with Ca2+ as a reference cation. The weak‐field electrical conductivities of suspensions of the top and bottom horizons and OM‐free black soil samples were 0.021 to 0.033, 0.011 to 0.021, and 0.0065 to 0.0082 mS cm−1, respectively. The mean free binding energies of the cations in the same soil sample suspensions were 5.5 to 7.3, 7.3 to 9.3, and 9.6 to 10 kJ mol−1, respectively. The mean free adsorption energies of all cations increased with field strength and were in the order OM‐free &gt; bottom horizon &gt; top horizon. At field strengths &gt;100 kV cm−1, in the top‐horizon soil, the adsorption energies of Ca were 0.21 to 0.72 kJ mol−1, those of Cd and Cu were similar to one another at 0.01 to 0.25 kJ mol−1, and those of Pb were close to zero, while in the bottom horizon soil, the adsorption energies of the various cations were in descending order: Ca &gt; Cd &gt; Pb &gt; Cu, and in the OM‐free soil the order of the adsorption energies of the various cations were Cd ≈ Cu ≈ Ca &gt; Pb. The humus basically increased the negative electrokinetic potentials of the clay‐size‐fraction particles of the three black soil samples saturated with Ca, Cd, Cu, or Pb.

Soft X-ray spectromicroscopy study of mineral-organic matter associations in pasture soil clay fractions.

There is a growing acceptance that associations with soil minerals may be the most important overarching stabilization mechanism for soil organic matter. However, direct investigation of organo-mineral associations has been hampered by a lack of methods that can simultaneously characterize organic matter (OM) and soil minerals. In this study, STXM-NEXAFS spectroscopy at the C 1s, Ca 2p, Fe 2p, Al 1s, and Si 1s edges was used to investigate C associations with Ca, Fe, Al, and Si species in soil clay fractions from an upland pasture hillslope. Bulk techniques including C and N NEXAFS, Fe K-edge EXAFS spectroscopy, and XRD were applied to provide additional information. Results demonstrated that C was associated with Ca, Fe, Al, and Si with no separate phase in soil clay particles. In soil clay particles, the pervasive C forms were aromatic C, carboxyl C, and polysaccharides with the relative abundance of carboxyl C and polysaccharides varying spatially at the submicrometer scale. Only limited regions in the soil clay particles had aliphatic C. Good C-Ca spatial correlations were found for soil clay particles with no CaCO3, suggesting a strong role of Ca in organo-mineral assemblage formation. Fe EXAFS showed that about 50% of the total Fe in soils was contained in Fe oxides, whereas Fe-bearing aluminosilicates (vermiculite and Illite) accounted for another 50%. Fe oxides in the soil were mainly crystalline goethite and hematite, with lesser amounts of poorly crystalline ferrihydrite. XRD revealed that soil clay aluminosilicates were hydroxy-interlayered vermiculite, Illite, and kaolinite. C showed similar correlation with Fe to Al and Si, implying a similar association of Fe oxides and aluminosilicates with organic matter in organo-mineral associations. These direct microscopic determinations can help improve understanding of organo-mineral interactions in soils.

Correlation of unsupported 210Pb activity in soil and moss

The activities of unsupported 210Pb, a naturally occurring radionuclide, were measured in samples of soil and terrestrial mosses collected in Serbia. Considering that clay particles in soil have a high affinity for Pb adsorption, and that mosses usually capture aerosol particles to obtain necessary nutrients, measurable amounts of airborne 210Pb, the daughter of 222Rn, can be registered in both soil and mosses. The objective of the present study was to determine if it is possible to compare the activity of unsupported 210Pb in soil and moss collected at the same sampling site, and to establish if a correlation exists between these measured values.

Organic Carbon and Nitrogen Associated with Soil Aggregates and Particle Sizes Under Different Land Uses in Tigray, Northern Ethiopia

AbstractSoil aggregation serves as storage and cycling of soil organic carbon (SOC) and total nitrogen (TN), which are essential for the functioning of terrestrial ecosystems. Thus, aggregate and particle associated SOC and TN in 0‐ to 10‐cm and 10‐ to 20‐cm layers were estimated for five land uses: rainfed cultivation (RF), agroforestry (AF), open pasture (OP), silvopasture (SP), and irrigation (IR) each with five replications within a watershed in Ethiopia. OP had the highest WSA &gt; 2 mm (88·7%) and SOC associated with macroaggregates (20·0 g kg−1), which were significantly higher (P &lt; 0·0001; P = 0·0017 for WSA and SOC, respectively) than that in other land uses in 0‐ to 10‐cm depth. SOC associated with both macroaggregates and microaggregates decreased with depth. Macroaggregates contained higher SOC than microaggregates in both layers under all land uses. AF had the highest SOC associated with microaggregates (2·6 g kg−1) followed by that in SP (2·3 g kg−1), indicating its potential to stabilize SOC more than other land uses. TN associated with macroaggregates followed a trend similar to that of SOC. OP had also significantly higher SOC (P = 0·0001) and TN (P = 0·0004) associated with sand particles than RF, AF, and IR. Sand‐associated SOC and TN were the highest in uncultivated systems. Moreover, the higher SOC concentrations associated with clay particles in soils under OP, SP, and AF showed that grass‐based and tree‐based systems are rich in stable SOC as clay‐associated SOC has higher residence time than that associated with sand or silt fractions. Copyright © 2013 John Wiley &amp; Sons, Ltd.

Fate of Cryptosporidium parvum oocysts within soil, water, and Plant environment

Vegetative Filter Strips (VFS) have long been used to control the movement of agricultural nutrients and prevent them from reaching receiving waters. Earlier studies have shown that VFS also dramatically reduce both the kinetics and extent of Cryptosporidium parvum (C. parvum) oocysts overland transport. In this study, we investigated possible mechanisms responsible for the ability of VFS to reduce oocyst overland transport. Measurement of the kinetics of C. parvum adhesion to individual sand, silt, and clay soil particles revealed that oocysts associate over time, albeit relatively slow, with clay but not silt or sand particles. Measurement of oocyst overland transport kinetics, soil infiltration depth, distance of travel, and adhesion to vegetation on bare and vegetated soil surfaces indicate that oocysts move more slowly, and penetrate the soil profile to a greater extent on a vegetated surface than on a bare soil surface. Furthermore, we demonstrate a small fraction of the oocysts become attached to vegetation at the soil-vegetation interface on VFS. These results suggest VFS function to reduce oocyst overland transport by primarily decreasing oocyst surface flow enough to allow penetration within the soil profile followed by subsequent adhesion to or entrapment within clay particle aggregates, and to a lesser extent, adhesion to the surface vegetation.

Soil properties and environmental tracers: A DEM based assessment in an Australian Mediterranean environment

Terrain properties vary at the hillslope and catchment scale and play a significant role in the distribution of water and sediment. Of particular interest in recent years has been the role of hillslope and catchment properties in the spatial and temporal distribution of soil organic carbon (SOC) and the ability to predict SOC from DEM terrain analysis. SOC plays a significant role in soil health and productivity as well as providing a significant store of terrestrial carbon. This study examined SOC concentration along representative pasture transects in a catchment located in southern Western Australia with a Mediterranean climate. Results demonstrate that the majority of SOC (%) is located in the near-surface (300mm) and is concentrated in the top 0.2m. There was no relationship found between SOC (or microbial biomass) and topography or topographic derivatives such as wetness and terrain indices from DEMs. Significant relationships were however found between SOC and environmental tracers (137Cs and 210Pbex) down the soil profile. Weak, yet significant, relationships were found between SOC and the environmental tracers along the hillslope transects, suggesting that organic carbon moves along the same pathways as clay particles in soil. An erosion assessment using 137Cs and also a numerical soil erosion and landscape evolution model found low and comparable erosion rates at the site. The results demonstrate that SOC concentration is relatively uniform across the study site and that a transect scale assessment can provide a measure of hillslope and catchment scale SOC in this environment.

Monoterpenes of Salvia leucophylla

The “ Salvia phenomenon” is one of the most famous examples of allelopathic interaction between higher plants. The Salvia thickets are surrounded by zones of bare soil (“bare zone”, 1-3 m in width), which merge into areas of inhibited grassland (“zone of inhibition”) and finally undisturbed grassland at a distance of 3-9 m. This characteristic vegetation pattern was attributed to monoterpenes, especially 1,8-cineole and camphor, which volatilized from S. leucophylla leaves, got adsorbed in the soil around the Salvia thickets, and inhibited germination and seedling growth of annual herbs. Initially, continuity of hydrophobic environment (clay soil particles – cuticular waxes on the seed/seedling surfaces – plasmodesmata - plasma membrane) was regarded to be important for the lipophilic compounds to enter the target cells. However, monoterpenes can reach the target cells via aqueous route as well. Because monoterpenes produced by S. leucophylla all induce similar symptoms in the seedlings of target plants, their mode of action appears to be essentially common. They exert various deteriorating effects on the cells of target plants, which might be totally explained if the primary point of action resides in mitochondrial function (respiratory ATP synthesis) and/or generation of reactive oxygen species. In contrast to the previous belief that cuticular waxes act as the pathway of lipophilic monoterpene to enter the site of action or reservoir of the inhibitors, they may act as “adsorptive barrier” to prevent the entering of monoterpenes inside the cell wall.

Evaluating pore structures of soil components with a combination of “conventional” and hyperpolarised 129Xe NMR studies

129Xe nuclear magnetic resonance (NMR) spectroscopic studies of xenon gas adsorbed on model systems representing soil porous components (Al (hyrd)oxides and charcoals) as well as natural soil materials (derived from a non-allophanic Andosol) were performed with the aim of characterising their micro- (< 2 nm) and mesopores (2–50 nm). Both conventional, i.e. thermally polarised (TP), and laser-polarised or hyperpolarised (HP) 129Xe NMR was applied. The latter technique significantly increased sensitivity of the measurements. Information on the pore size range was derived from the 129Xe resonance shifts, δ, monitored as function of Xe loading, whereas the temperature dependences of δ provided information on the nature of xenon–pore surface interactions in terms of effective adsorption enthalpies. Dissolved organic matter (DOM) sorption on the mesoporous Al 2O 3 was shown to proceed inhomogeneously indicative by the Xe adsorption enthalpies corresponding to the co-existing “empty” pores and pores coated with organic species. In AlOOH, an interconnected system of micro- and mesopores was tested. The enhanced sensitivity of HP 129Xe NMR allowed us detecting micropores in charcoals, where N 2 adsorption method underestimated porosity due to the restricted N 2 diffusion at 77 K. The interconnected pore structure of charcoals was attributed to the voids formed by both polyaromatic and aliphatic domains (evidenced by 13C NMR). The observed differences between the TP- and HP 129Xe NMR patterns were explained by the restricted xenon diffusion through charcoal particles caused by the constricted pore openings. Their suggested size is of the order of one or two diameters of the Xe atom. For the Andosol clay fractions, the large low-field 129Xe shifts (up to 175 ppm) increasing with Xe pressure indicated a developed porosity most obviously comprised by the interconnected micro- and mesopores. Such porous network may originate from the “multi-domain” structure of soil clay particles, i.e. particles formed by agglomerated nano-sized crystallites. The latter are assumed to be the polynuclear Al x (H 2O) y (OH) z clusters formed by hydrolysis reactions of Al 3+ species after the destroying of Al-humus complexes by the H 2O 2-oxidation.

Detergency of clay soil particles from cotton, nylon and polyester by ethanol solution with nonionic surfactant

Detergency of clay soil particles from cotton, nylon and polyester by ethanol solution with nonionic surfactant

Amelioration of saline–sodic soil with mildly saline water in the Songnen Plain, northeast China

Abstract. The saline–sodic soils of the dryland Songnen Plain in northeast China are only slowly permeable to fresh water because of their large content of montmorillinite clay and sodium bicarbonate. Use of slightly saline groundwater containing adequate dissolved calcium and magnesium for leaching and reclamation can potentially prevent dispersion of the clay soil particles during treatment. Amelioration was evaluated using shallow, mildly saline groundwater to irrigate sorghum–corn rotations in a two‐year field experiment. After two growing seasons during which a total of 400 mm of leaching water was applied, in addition to some supplemental irrigation water, the average electrical conductivity (ECe) of the top 1.2 m of the soil profile decreased from 14.5±3.5 to 2.7±0.2 dS m−1, and the sodium absorption ratio (SARe) decreased from 35.3±4.1 to 10.1±2.5 (meq L−1)0.5. The soil physical properties were improved: infiltration rate with mildly saline groundwater increased from 12.1 to 42 mm h−1. Salinity changes in the top 1.2 m of soil layers after 700 mm of leaching produced no further improvement. Crop yields produced on plots undergoing amelioration increased by 64–562% compared with the rainfed control. The improved soil conditions after leaching resulted in 59–548% greater crop yields.

Hydrocyclone for pre-filtering of irrigation water

The use of water containing suspended sediments causes serious problems to irrigation systems. Choosing the right filtering system type and capacity is essential to avoid increases in operational and maintenance costs of irrigation resulting from the need for cleaning and frequent component replacing. Pre-filters, such as the hydrocyclone, are important for their significant capability of retaining particles suspended in the water. Data on hydrocyclones performance for pre-filtering of irrigation water can be found in the literature, but research data in Brazil are scarce. Therefore, four Rietema type hydrocyclones (50 mm diameter) were constructed, one with circular-end and the other three presenting rectangular-end feeding tubes. The evaluation of hydrocyclones performance was conducted by using suspensions of fine sand and clay soil particles under varied pressure differentials. The comparison criteria were the discharge and the separation capability, given by total efficiency and reduced total efficiency. The hydrocyclone with circular-end feeding tube presented the highest indexes for the adopted criteria, considering sand and soil suspensions.

Saturated hydraulic conductivity of a volcanic ash soil affected by repulsive potential energy in a multivalent anionic system

Acid rain is supposed to influence soil structures, because soils have pH-dependent charges. The adverse effects of acid rain on soils must be assessed. Although repulsive potential energy among soil clay particles generates swelling and dispersion, thereby changing the soil’s hydraulic conductivity, the relationship between hydraulic conductivity and repulsive potential energy has not been evaluated. Moreover, research into repulsive potential energy in multivalent counterionic systems has been rare. In this paper, repulsive potential energies for a volcanic ash soil (allophanic Andisol), which is characterized by a number of pH-dependent charges, were evaluated in a multivalent counterionic system. Changes in saturated hydraulic conductivity (K) of volcanic ash soil during dilute acid leaching and their relationship with the repulsive potential energies were examined. When nitric acid at pH 3 or 4 was leached, K decreased rapidly. On the other hand, the decrease in K attenuated as the proportion of sulfate in the dilute acid increased. Electrophoretic mobilities were measured and the zeta potentials were estimated. From the zeta potentials and the calculation of repulsive potential energies between the clay particles in the NO3–SO4 system, we concluded that the decrease in K for an acid solution with a high proportion of nitrate was due to swelling and dispersion of the soil induced by electrostatic repulsive potential energy. Because sulfate formed complexes on the clay surface, the repulsive potential energy decreased as the proportion of sulfate in the dilute acid increased. Then, the flocculation of the soil was maintained, thereby inhibiting the decrease in K.

Detergency of clay soil particles in a water/ethanol mixture (III)

Detergency of clay soil particles in a water/ethanol mixture (III)

Aggregation of clay in the hydrometer test

Recent studies have compared particle-size analysis methods for soils containing fine clay particles. The results showed significant differences between the techniques. This study consisted of a series of hydrometer experiments designed to give greater understanding of the behavior of kaolinite clay during the ASTM 422-63 hydrometer test. The results were consistent with the aggregation of fine clay particles, possibly due to the known hydrolysis behavior of the sodium polyphosphate dispersants used in the experiment. To avoid a serious underestimation of the fraction of submicron clay particles in soils, dispersants that do not suffer from time-dependent hydrolysis should be evaluated for the hydrometer test.

Electron microprobe and electron microscope studies of soil clay particles

Several soils were examined in detail by electron microscope and microprobe to assess the nature of clay size particles and microaggregates. Morphology, analytical composition, identity and association between particles were determined. Of the mineral oxides, pellets of goethite and hematite about 1 �m in size were most distinctive. They were found in all the soils examined except one. They contained both aluminium and silicon, sometimes in fairly constant proportions, but the presence of adhering fine material made it difficult to assess the extent to which these elements were part of the iron oxide structure. Discrete gibbsite particles of micron size were rarely encountered, although some soils contained appreciable quantities of it in much smaller form. At least a few rutile or anatase particles were found in all soils, while they were common in some. They also were usually contaminated by surface deposits, in contrast to ilmenite and quartz grains which were always relatively clean and were often isolated from other particles. The ratios of ironltitanium in ilmenites were well defined but different from soil to soil. Uncontaminated clay mineral particles were rare. Most had substantial deposits of fine-grained material upon their surfaces, much of it &lt; 200 A in diameter. The most easily detected components of these surface deposits were goethite and hematite, and often they were dominant. Finely divided clay minerals were usually present as well, together in some soils with gibbsite and occasionally with titanium oxides. In one soil where coarser (1 �m) host particles were not readily available to carry it, the fine-grained material formed microaggregates consisting of kaolin, gibbsite and hematite, all of comparable size. Soils containing both kaolin and illite were composed mainly of compact microaggregates of the two clay minerals, which had the appearance of single particles. These results demonstrate the close association frequently existing between micron and submicron soil particles and between submicron particles themselves. The structural units of soil particles were often much smaller than generally supposed.

Studies on the Cataphoresis of Soil Clay Particles: I

Abstract The many important physical and chemical reactions which occur in soils are ascribed to the clay fraction of soils. Therefore, soil physics and soil chemistry are truly based on the colloidal phenomena of soil clays.