Clay Cation Exchange Capacity Research Articles

Role of clay cation exchange capacity, location of charge, and clay mineralogy on potassium availability in Indian Vertisols

Abstract Precise information on the location of charge in clay minerals and their charge density in smectite-dominant soils is rare. The present study was undertaken with three benchmark Vertisols to establish the relationship between the clay cation exchange capacity (CEC), charge density, as well as the location of charge in smectitic soil clay minerals and their relationship with potassium (K) fixation and release. Potassium fractions and their threshold levels in the Vertisols were determined by standard methods. Soils were segregated into silt, total clay and fine clay fractions for X-ray diffraction analysis and fine clay fractions were used to determine the CEC using standard methods. The Hofmann-Klemen effect (HK) and modified Greene-Kelly test was done with the fine clay to determine the CEC of the tetrahedral sheet. Subsequently, the CEC of the octahedral sheet was calculated as the difference between total CEC and the tetrahedral CEC. The results showed that ~60–64% of the total CEC is attributed to the tetrahedral layers. The tetrahedral CEC that is proportional to the tetrahedral charge density was significant and negatively correlated with K release threshold values and all fractions of K. The tetrahedral CEC contributed more toward the K fixation and release than the octahedral CEC. The study shows that the dominant presence of high-charge smectites in the fine clay fractions of these Vertisols contributed to the tetrahedral CEC and consequently to the charge density of these soils, which implied a tendency to fix K easily and release it with greater difficulty compared to soils with low-charge smectites.

Cotransport of fullerene nanoparticles and montmorillonite colloids in porous media: Critical role of divalent cations of montmorillonite

While the cotransport of carbon nanoparticles (CNPs) and clay colloids in porous media has been widely studied, the influence of the cation exchange capacity (CEC) of clay colloids on the transport process remains unclear. In this study, batch adsorption and column transport experiments were conducted to investigate the fate and transport of CNPs and clay colloids in quartz sand, with respect to the effect of monovalent-cation exchange capacity (mono-CEC), divalent-cation exchange capacity (di-CEC) and total CEC of clays. Fullerene nanoparticles (nC60) and six types of montmorillonite (ML) with different CEC were selected as modeled CNPs and clay colloids, respectively. Transport behavior of nC60 and ML was characterized using breakthrough curves (BTCs) and fitted with two-kinetic-sites colloid transport model. Results of the adsorption experiments showed a good linear correlation between the deposition of nC60 on the sand surface and the di-CEC of ML. Transport of ML and nC60 was inhibited by each other. The calculated mass recovery of nC60, as well as the fitted maximum deposition capacity and attachment rate coefficients of nC60 exhibited a strong linear relationship with the di-CEC of ML. These results indicate that divalent cations in ML interlayers play a significant role in aggregation between nC60 and ML and their cotransport. Through measurements of the particle size and zeta potentials of sole nC60 and mixtures of ML and nC60, FTIR and XPS analysis of nC60 under different conditions, and a release experiment of nC60 in a sand column, it demonstrated cation bridging (Ca2+-π) between nC60 and ML mediated by the divalent cations in ML interlayers. The study highlighted the potential of using di-CEC of clays as an indicator to predict the mobility of nC60 in clay-containing porous media and added insights to the transport behavior of CNPs in porous media.

Development of Soil Fertility Index Using Machine Learning and Visible-Near-Infrared Spectroscopy

An accurate assessment of soil fertility is crucial for monitoring environmental dynamics, improving agricultural productivity, and achieving sustainable land management and utilization. The inherent complexity and spatiotemporal heterogeneity of soils result in significant challenges in soil fertility assessment. Therefore, this study focused on developing a rapid, economical, and precise approach to evaluate soil fertility through the application of visible-near-infrared spectroscopy (VNIR). To achieve this, we utilized the Land Use and Cover Area Frame Survey (LUCAS) dataset and employed a variety of prediction models, including partial least squares regression, support vector machines (SVMs), random forest, and convolutional neural networks, to estimate various soil properties and overall soil fertility. The results showed that the SVM model had the highest prediction accuracy, particularly for clay content (coefficient of determination (R2) = 0.79, ratio of performance to interquartile range (RPIQ) = 3.04), pH (R2 = 0.84, RPIQ = 4.54), total nitrogen (N) (R2 = 0.80, RPIQ = 2.40), and cation exchange capacity (CEC) (R2 = 0.83, RPIQ = 3.16). A soil fertility index (SFI) was developed based on factor analysis, integrating nine essential soil properties: clay content, silt content, sand content, pH, carbonate content, N, soluble phosphorus, soluble potassium, and CEC. We compared direct and indirect prediction models for estimating SFI and found that both models showed high accuracy (mean value of R2 = 0.80, mean value of RPIQ = 2.21). Additionally, SFI was classified into five classes to provide insights for precision agriculture. The kappa coefficient was 0.63, which indicated that the SFI evaluation results between VNIR and chemical analysis were relatively consistent. This study provides a theoretical foundation of real-time soil fertility monitoring for the optimization of agricultural practices.

Determination of useful boron content of the soils of Kırıkhan-Kumlu region of Hatay province and their relationship with some soil properties

In this study, it was aimed to determine the useful boron content of the soils of Kırıkhan-Kumlu region of Hatay province and its relationships with some physical and chemical properties. For this purpose, a total of 60 soil samples were taken from 0-20 and 20-40 cm depths and from 30 different points to represent the study area. The pH, total salt, composition, cation exchange capacity (CEC), lime, organic matter and useful boron contents of the soils were determined. According to the results of the research; pH contents of the soils were 7.95-8.43; total salt contents 0.009-0.115 %; clay contents 18.88-74.16 %; sand contents 7.12-59.84 %; silt contents 15.28-52.72 %; lime contents 0.47-26.59 %; organic matter contents 1.16-6.08 %; CEC contents 22.26-72.83 me/100 g and useful boron contents 0.10-1.25 mg/kg. In terms of useful boron content of Kırıkhan-Kumlu soils of Hatay province, it was determined that 50.00 % of them were very low, 40.00 % were low and 10.00 % were sufficient at 0-20 cm depth and 50.00 % of them were very low, 43.34 % were low and 6.66 % were sufficient at 20-40 cm depth. While a positive significant relationship was determined between useful boron and salt, clay, lime and CEC contents of soils, a negative significant relationship was determined between useful boron and sand content. Positive significant relationships were determined between salt and clay, lime and CEC contents of the soils, while negative significant relationships were determined between salt and pH and sand contents. Positive significant relationships were determined between clay and organic matter and CEC contents of the study area soils, while negative significant relationships were determined between clay and sand and silt contents. Significant negative relationships were determined between sand and organic matter and CEC contents of the soils. At the same time, while negative significant relationships were determined between silt and CEC and lime and organic matter contents of the soils, positive significant relationships were determined between organic matter and CEC. As a result, it was seen that the useful boron content of the soils in the study area was determined at low and very low levels above 92 % in all soils of the study area and it was seen that the useful boron content of the soils was insufficient and therefore boron fertilization should be done.

Fractal Features of Soil Particles as an Index of Land Degradation under Different Land-Use Patterns and Slope-Aspects

This study examines the effects of land use and slope aspect on soil erodibility (K-factor) and the fractal dimension (D) of soil particle size distribution (PSD) in calcareous soils at the watershed scale in western Iran. The study analyzed 113 soil samples collected from four land uses (slope-farmland, farmland, pasture, and woodland) at a depth of 0–20 cm, measuring common soil properties such as soil texture, soil organic matter (SOM), calcium carbonate (CaCO3), pH, and cation exchange capacity (CEC). The PSD of soil samples was measured using the international system of soil size fractions, and the D for PSD was calculated. The K-factor was calculated using the RUSLE model. The results showed that the K-factor was highest in slope farmlands with SOM at 1.6% and lowest in woodlands at 0.02 Mg h MJ−1 mm−1 with SOM at 3.5%. The study also found that there were significant correlations between D and clay content (r = 0.52), sand content (r = −0.29), and CEC (r = 0.36). Woodland soils had the highest SOM content, with a mean D value of 2.895, significantly higher than the mean D value of slope farmland soils, which had the lowest SOM at 1.6%. The study concludes that woodland soils retain finer particles, particularly clay, resulting in lower soil loss and land degradation compared to other land uses. Finally, the study suggests that shady slope aspects (south aspect) contain more organic matter due to less solar radiation and higher soil water content, resulting in lower soil erodibility (0.02 Mg h MJ−1 mm−1) and higher D values compared to other slope aspects.

Phosphorus extractability in relation to soil properties in different fields of fruit orchards under similar ecological conditions of Pakistan

Productivity of an orchard generally depends upon the fertility of the soil and the nutrient requirements of the fruit trees. Phosphorus (P) extractability from soils influences the P sorption, release patterns, and P bioavailability. A study was carried out to investigate P extractability via seven extraction methods in relation to soil properties in three fruit orchards. In total, 10 soil samples were collected from each fruit orchard, namely, citrus (Citrus sinensis L.), loquat (Eriobotrya japonica L.), and guava (Psidium guajava L.), located in similar ecological conditions to the Haripur district of Pakistan. Available P in the soil was extracted using deionized H2O, CaCl2, Mehlich 1, Bray 1, Olsen, HCl, and DTPA methods. Selected soil properties [pH, electrical conductivity (EC), soil organic matter (SOM)], texture, cation exchange capacity (CEC), macronutrients, and micronutrients were also determined. Soils sampled from orchards indicated significant differences in soil properties. Orchards have sequestered more amount of C stock in soil than without an orchard. The extractability of P from soils was profoundly affected by P extraction methods. The average amount of extractable P was relatively higher in those soils where the total amount of P was also higher. These methods extracted different pools of soil P with varying P concentrations regulated by the soil properties. Phosphorus amounts extracted were varied in the order of HCl > DTPA > Mehlich 1 > Bray 1 > Olsen > CaCl2 > water. Among orchards, a higher amount of P was found in soils of loquat followed by citrus and guava orchards. Regardless of the method, subsurface soil got a lower concentration of extractable P than surface soil in all orchards. The extractable P was highly associated with soil properties. DTPA extractable P was related to SOM soil clay content and CEC by R2 values of 0.83, 0.87, and 0.78, respectively. Most of the extraction methods were positively correlated with each other. This study indicated that SOM inputs and turnover associated with orchard trees exhibited a substantial quantity of extractable P in soils. Predicting available P in relation to its bioavailability using these methods in contrasting soils is required.

Pore-scale modelling on complex-conductivity responses of hydrate-bearing clayey sediments: Implications for evaluating hydrate saturation and clay content

A majority of the accumulated gas hydrates exist in fine-grained unconsolidated sediments with clays, which pose challenges to reservoir evaluation with resistivity-based techniques. Characteristic electrical parameters derived from induced polarization (IP) measurements have potentials to describe complex formations of various lithology, pore-water salinities, and different depths from the borehole. However, there is still a knowledge gap in complex-conductivity properties of the hydrate-bearing clayey sediments. We present a pore-scale numerical study on modelling the low-frequency (<1 kHz) complex-conductivity spectra of clayey sediments containing hydrates based on the finite-element approach, with an emphasis on evaluating the hydrate saturation (sh) and clay content. Firstly, the influences of clay type, distribution form, content and sh on the complex conductivity of sediments containing hydrates were examined systematically. Secondly, power-law and linear correlations were established for evaluating the hydrate saturation and clay content, respectively, based on complex-conductivity parameters. (Effects of clay type) The in-phase conductivity of hydrate-bearing smectite is significantly higher than that of hydrate-bearing illite and kaolinite due to the higher cation exchange capacity (CEC) of smectite. Higher peak frequency and quadrature conductivity appear for the hydrate-bearing kaolinite case because the mobility of counterions in the Stern layer of kaolinite is about ten times of that for smectite and illite. (Effects of clay distribution form) The coating-clay case has much lower in-phase and quadrature conductivities than the dispersed- and laminated-clay cases because the coating clay isolates sand particles from the pore water and no electrical double layer (EDL) forms around the sand particles. (Effects of clay content) With an increasing content of the structural clay up to 60%, the in-phase conductivity decreases and increases in the frequency bands lower and higher, respectively, than the peak frequency corresponding to the EDL polarization. The effective dielectric constant increases consistently with the clay content due to the much higher CEC of clays than that of sands. (Effects of hydrate saturation) The in-phase conductivity decreases consistently with an increasing sh up to 0.40 due to the negligible conductivity of hydrates and blockage effect on conduction currents. Both the quadrature conductivity and effective dielectric constant in the EDL-polarization-dominant frequency band decrease with an increasing sh. In this work, it has been evidenced that complex-conductivity responses of hydrate-bearing clayey sediments can be understood theoretically and modelled numerically based on the interpretation of electrical conduction and electrochemical polarization mechanisms of EDLs. This study provides a theoretical and modelling foundation for the development of new IP-based geophysical techniques for hydrate-reservoir evaluation and monitoring in both the exploration and exploitation stages.

Modified Compositions of Micelle–Clay and Liposome–Clay Composites for Optimal Removal from Water of Bacteria and Hydrophobic Neutral Chemicals

The efficiency in water treatment by granulated complexes formed from the clay bentonite with (i) micelles of the cations of octadecyltrimethyl-ammonium (ODTMA) or (ii) liposomes of didodecyldimethyl-ammonium (DDAB) was investigated. The bentonite–ODTMA complexes were synthesized in three variations: I. mass ratio of 68/32, which resulted in an excess of positive charge of half of the clay cation exchange capacity and is denoted “ordinary”; II. complexes having higher loads of ODTMA, denoted “enriched”; and III. “neutral”. These variations were designed to optimize the efficiency and reduce the costs of water treatment. “Ordinary” and “neutral” complexes of DDAB were also synthesized. The “ordinary” complex of ODTMA was shown to be efficient in the removal of anionic/hydrophobic molecules and bacteria. The “enriched” complexes were more active in removal of bacteria from water by filtration due to the higher release of free ODTMA cations, which causes biostatic/biocidal effects. The corresponding “ordinary” and “neutral” complexes of ODTMA and DDAB yielded the same efficiency in removal from water of the neutral and hydrophobic herbicides, S-metolachlor (i) and alachlor (ii), respectively. Model calculations, which considered sorption/desorption and convection yielded simulations and predictions of filtration results of the herbicides. The neutral complexes are advantageous since their production saves about 1/3 of the amount of ODTMA or DDAB, which constitutes the expensive component in the respective composite.

Characteristics of soils of lower Indo-Gangetic plains of West Bengal under rice cultivation

Five typical pedons developed from alluvium on lower Indo-Gangetic plain under major land use system of rice from Murshidabad district, West Bengal were studied for their morphological, physical and chemical characteristics. Soils were very deep with varying texture and drainage classes and have some common characters during pedogenesis under impeded drainage condition. Soils were characterized by the redoximorphic features viz., mottle in the form of segregation of Fe-Mn depletion or gleying, mostly in the sub-surface to sub-soil. Soils were strongly acidic (pH 5.1) to slightly alkaline in the surface and neutral (pH 6.5 to 7.5) in the sub-surface to sub-soil, low to high in soil organic carbon (SOC) content (0.40 to 9.60 g kg−1), low to medium in cation exchange capacity (CEC) [4.0 to 42.0 cmol(p+)kg−1] with high base saturation (61 to 90%). Among the exchangeable bases, Ca2+ is the dominant cation followed by Mg2+, Na+ and K+. Low to medium CEC of soil indicates the mineralogy of the soil as kaolinite and illite (mica). However, clay CEC value indicates the presence of smectite along with hydroxyl-interlayered vermiculite. The high clay CEC value with neutral soil reaction and high content of Ca2+ indicates the dominance of smectite in the soils of pedons 2 and 3. The SOC stock suggested implementation of appropriate conservation measures to the soils of young alluvial plains to improve the quality of soil. The soils of old alluvial plains are generally more fertile in comparison to that of the young alluvial plains. The study indicates that land use has got significant effect on soil characteristics, influencing the soil fertility.

Estimating cation exchange capacity and clay content from agricultural soil testing data

Clay content and the ability to reversibly retain cations affect many essential chemical and physical properties of soil, such as pH buffering and carbon sequestration. Cation exchange capacity (CEC) and base saturation are also commonly used as criteria in soil classification. However, determination of CEC and particle-size distribution is laborious and not included in routine soil testing. In this study, pedotransfer functions including soil test cations (STCat; Ca2+ + Mg2+ + K+), pH and soil organic carbon (SOC, %) as explanatory variables were developed for estimating CEC, titratable acidity (TA; H+ + Al3+) and clay content (clay, %). In addition, reference values for potential CEC and its components were determined for Finnish mineral and organic soils. The mean of potential CEC extracted by 1 M ammonium acetate at pH 7.0 ranged from 14 (range 6.4−25) in coarse soils to 33 (21−45) cmol(+) kg-1 in heavy clay soils, and from 42 (24−82) in mull soils to 77 (25−138) cmol(+) kg-1 in peat soils. The average CEC of clay and SOC were 27 and 160 cmol(+) kg-1, respectively. Titratable acidity occupied 53% and around 40% of the CEC sites in organic and mineral soils, respectively, evidencing that it is a prominent component of the potential CEC in these predominantly acidic soils. STCat, pH and SOC explained 96% of the variation in potential CEC. STCat and pH can be used in estimating the clay content especially for soils containing over 30% clay. In coarse textured soils, in contrast, SOC hampers the STCat based estimation of clay content.

Estimating Atterberg limits of soils from hygroscopic water content

A number of environmental, agronomic and engineering applications require knowledge of the Atterberg limits (liquid limit, LL; plastic limit, PL) and the plasticity index, PI of soils. The tedious and costly nature of standard experimental methods, as well as challenges with measurement repeatability motivated the development of regressions as well as more sophisticated techniques to estimate the Atterberg limits from other properties such as clay content, cation exchange capacity (CEC), and soil specific surface area. The amount of water adsorbed to particle surfaces at relative humidity (RH) < 95% is intimately linked to these soil properties, which suggests that hygroscopic water content (wh) may be a better predictor of the Atterberg limits. The present study (i) proposes regression models that estimate the LL, PL, and PI from wh at different relative humidity values ranging from 10 to 90% and considering water sorption hysteresis, and (ii) compares the performance of the models to other models that comprise clay, silt and organic carbon contents and CEC. For model development, wh was measured by water adsorption and desorption for 168 soil samples that varied widely in terms of geographic origin, clay mineralogy, and soil organic carbon content. The LL and PL were determined with the drop cone penetrometer and rolling device, respectively. Regression models were developed for both sorption directions for nine RH values between 10 and 90%. For 44 independent soil samples, the models estimated LL, PL and PI accurately (e.g., for desorption wh measured at 90% RH, RMSE and r2 values were 6.43% & 0.89; 3.95% & 0.83 and 6.69% & 0.79, respectively). There was no clear effect of sorption direction on the estimation accuracy. The wh determined at higher RH tended to better estimate the Atterberg limits compared to that measured at lower RH. The wh models were superior in estimating LL and PL compared to models that were based on clay content and organic carbon or CEC. For the PI, the models based on CEC performed slightly better than the wh models. Thus, a single measure of wh can provide reliable estimates of the Atterberg limits and PI.

Soil Development from Volcanic Ash Based on Different Pyroclastic Composition

Potential volcano in several provinces in Indonesia played a significant role in the formation and quality of soil development. Soils that developed from the volcanic ashes often thought to contribute greatly to improve soil fertility, without regard to the nature and composition of the volcanic ash produced. Volcanic ash generated from the results in volcanic activity has a different composition, there are basaltic, andesitic and granitic, thereby affecting the process of formation and characteristics of the soil. The Objective of this study is to determine the soil development from different types of pyroclastic generated from Lokon volcano in North Sulawesi. The coordinates of research was in 1o 21' 18.0" N and 124o 49' 20.2"E. this research used ARL Quant X (EDXRF Analyzer) for X-Ray Fluorescence (XRF), Shimadzu XRD-7000 for X-Ray Diffractometer (XRD), geology map (scale 1:250,000), topographic map (scale 1:50,000), XRD software, GIS 10.3 software. Soil analysis for texture, pH, C-Organic, and cation exchange capacity (CEC). There are two types of pyroclastic as the source of soil development from volcanic ash, there are; 1) basaltic pyroclastic with 43.26% Si02 that are resulted from the first magmatic eruption and 2) andesitic pyroclastic with 5.09% Si02 that are resulted from the late magmatic eruption. Basaltic pyroclastic contains Fe 37.63%, Al 11.35%, Ca 13.17% and Mg 5.69%, while andesitic pyroclastic contains Fe 38.35%, Al 6.87%, and Ca 8.61%. Rainfall ranges from 2000-3500 mm/yr helped the soil formation and influenced the character of the soil, such as sandy loam of soil texture, 3.08% of soil C-organic content, 23.24 cmol+/kg of CEC and 148.93 cmol+/kg of clay CEC. Clay minerals content of the soil is vermiculite, kaolinite and, halloysite. Cation supply from basaltic pyroclastic influenced the formation of vermiculite mineral, whereas andesitic pyroclastic more influences the formation of the kaolinite mineral. Formation of soil texture with a predominance of the sand fraction is more influenced by the type of andesitic pyroclastic that more resistant to weathering processes.Keywords: Soil; volcanic ash; pyroclastic; vermiculite; kaolinite

Sediment clays are trapping heavy metals in urban lakes: An indicator for severe industrial and agricultural influence on coastal wetlands at the Mediterranean coast of Egypt

Coastal wetlands of the northern coast of Egypt have been impacted with higher loads of runoff, especially the large urbanized lakes of the Nile deltaic coast. Five urban lakes spanning the northern coast of Egypt (from east to west: Bardawil, Manzala, Burullus, Edku, and Mariut) were sampled for quantifying concentrations of heavy metals in their sediment and plant tissues. Sediment and plant tissues in lake Bardawil were the least contaminated, and the other lakes were moderately to highly polluted with Ni, Co, Cr, Pb, Zn, and Cu. Edku had the highest concentrations of Co, Cr, and Cu (19.83, 45.42 and 68.60 mg kg−1, respectively). The proportion of clay in sediment was significantly and positively correlated with Co and Ni in sediment (r = 0.7 and P ≤ 0.001), suggesting an important role of clay cation exchange capacity in the sorption of metals and removing them from the water column.

Mineralogical differences in a temperate cultivated soil arising from different agronomic processes and plant K-uptake

Potassium (K) is an essential plant nutrient mainly present in the crystal structure of K-bearing soil minerals (K-feldspars, micas). To assess the evolution of (clay) mineralogy due to K+ release from these minerals in continuously cultivated soils, samples were collected from long-term (1904–2014) field experiments submitted to contrasting crop rotations and amendments, with and without fertilisation. Soil samples were size-fractionated and mineralogy of the silt fraction and of clay subfractions was determined quantitatively by modelling X-ray diffraction (XRD) patterns. Clay subfractions were also analysed for their cation exchange capacity (CEC).Mineralogical data indicate the stability of clay mineralogy and the increased abundance of the finest clay subfraction at the expense of coarser ones, regardless of agronomic practices or amount of K removed by plants. This increase is accompanied by an increase in the bulk clay CEC owing to the major contribution of the finest clay subfraction to this parameter. Mineral dissolution, rather than alteration of mineral phases from coarse clay subfractions, most likely supplements K for plant nutrition in this soil. Dissolution is favoured over cation exchange owing to the dioctahedral character of micas and to their fine-grained granulometry. The observed long-term mineralogical resilience also indicates that part of plant nutrition is obtained from subsoil in a non K-limited context, whereas K supply through K-feldspar dissolution appears marginal.

Polyamidoamine as a clay modifier and curing agent in preparation of epoxy nanocomposites

In the present study the commercial multifunctional fatty acid polyamidoamine (PAA) was for the first time simultaneously applied as a curing agent and clay modifier for epoxy/clay nanocomposites (NC) based on diglycidyl ether of bisphenol A. The montmorillonite (Cloisite®Na+) was modified with different quantities of partially and fully protonated polyamidoamine. The NCs with 0.5 wt% novel organoclay were prepared by solution intercalation method. The major aims of this paper are investigations of the effects of the composition of PAA modified clays on structure, mechanical, barrier properties and corrosion stability on steel substrates of NCs were studied.The thermogravimetric, flame photometry and X-ray diffraction analyses confirmed the efficient modification of clay surface with polyamidoamine, predominantly located within layers. The NCs exhibited an intercalated/exfoliated morphology and the presence of free amino groups and increased content of modifier facilitated dispersion of clay particles within the polymer matrix, as shown by electron microscopy techniques (SEM, TEM). Under an optimized loading of PAA (molar quantity of total amino groups per clay cation exchange capacity of 1.75), the layers in stacks were separated by 5.0 nm and high number of individual layers was present in NC. Clay modified by PAA with free amino groups showed increased storage modulus in the rubbery state, glass transition temperature of NCs, while dumping factor was decreased. The tensile test confirmed that introduction of flexible modifier on the epoxy/clay interface lead to increase in the ultimate tensile strenght and elongation at break by 31% and toughness up to 83%. The electrochemical impedance spectroscopy and permeability tests proved the pronounced barrier effect of clay particles against corrosive species and water vapor when high dispersion degree of clay in NC was achieved.

Predicting spatial structure of soil physical and chemical properties of golf course fairways using an apparent electrical conductivity sensor

Soil apparent electrical conductivity (ECa) has been used to map spatial variability of soil properties in multiple cropping systems and may have applications in precision turfgrass management (PTM). The objective of this research was to determine whether ECa data could predict the spatial structure of soil properties relevant to turfgrass management. Research was conducted at the University of Georgia (UGA) and the Georgia Club (GC) golf courses in North GA during the summer of 2016. A mobile Veris Q1000 device was used to collect georeferenced ECa data from six golf course fairways (three per course). Soil samples were collected from each fairway using a georeferenced grid to determine clay content, soil pH, cation exchange capacity (CEC) and organic matter (OM). To understand the predictive relationship between ECa and soil properties, correlation coefficients and multiple linear regression models were generated for each fairway. Spatial maps were used to visually demonstrate these relationships. Though some relationships were observed between ECa and soil properties (primarily clay, soil pH and OM on the UGA course), measured parameters were insufficient to fully explain spatial variability in ECa. Findings from this study suggest that spatial variability of soil properties in turfgrass can be significant enough to warrant PTM. Though ECa may be used to partially predict clay content, CEC, OM and soil pH, additional research is required to better understand ECa variability and its applications for PTM. Future research exploring ECa for PTM should consider the roles of soil moisture, temporal variability and topography.

Incorporation of corn straw biochar inhibited the re-acidification of four acidic soils derived from different parent materials.

The effect of corn straw biochar on inhibiting the re-acidification of acid soils derived from different parent materials due to increased soil pH buffering capacity (pHBC) was investigated using indoor incubation and simulated acidification experiments. The incorporation of the biochar increased the pHBC of all four soils due to the increase in soil cation exchange capacity (CEC). When 5% biochar was incorporated, the pHBC was increased by 62, 27, 32, and 24% for the Ultisols derived from Tertiary red sandstone, Quaternary red earth, granite, and the Oxisol derived from basalt, respectively. Ca(OH)2 and the biochar were added to adjust the soil pH to the same values, and then HNO3 was added to acidify these amended soils. The results of this simulated acidification indicated that the decrease in soil pH induced by HNO3 was lower for the treatments with the biochar added than that of the treatments with Ca(OH)2 added. Consequently, the biochar could inhibit the re-acidification of the amended acid soils due to the increased resistance of the soils to acidification when the pH of amended soil was higher than 5.5. The inhibiting effectiveness of the biochar on soil re-acidification was greater in the Ultisol derived from Tertiary red sandstone due to its lower clay and organic matter contents and CEC than the other three soils. The incorporation of the biochar also decreased the potentially reactive Al, i.e., exchangeable Al, organically bound Al, and sorbed hydroxyl Al, compared with the treatments amended with Ca(OH)2. Therefore, the incorporation of corn straw biochar not only inhibited the re-acidification of amended acid soils through increasing their resistance to acidification but also decreased the potential of Al toxicity generated during re-acidification.

Comparing traditional and digital soil mapping at a district scale using residual maximum likelihood analysis

Conventional soil mapping uses field morphological observations to classify soil profiles into predefined classification systems and extrapolates the classified soils to make a map based on aerial photographs and the experience of the surveyor. A criticism of this approach is that the subjectivity of the surveyor leads to non-reproducible maps. Advances in computing and statistical analysis, and an increased availability of ancillary data have cumulatively led to an alternative, referred to as digital soil mapping (DSM). In this research, two agriculturally productive areas (i.e. Warren and Trangie) located in central New South Wales, Australia, were considered to evaluate whether pedoderms and soil profile classes defined according to the traditional approach can also be recognised and mapped using a DSM approach. First, we performed a fuzzy k-means analysis to look for clusters in the ancillary data, which include data from remote-sensed gamma-ray (γ-ray) spectrometry and proximal-sensed electromagnetic (EM) induction. We used the residual maximum likelihood method to evaluate the maps for various numbers of classes (k = 2–10) to minimise the mean square prediction error (σ2p,C) of soil physical (i.e. clay content, field capacity (FC), permanent wilting point (PWP) and available water content (AWC)) and chemical (pH, EC of 1 : 5 soil water extract (EC1:5) and cation exchange capacity (CEC)) properties of topsoil (0–0.3 m) and subsoil (0.6–0.9 m). In terms of prediction, the calculated σ2p,C was locally minimised for k = 8 when accounting for topsoil clay, FC, PWP, pH and CEC, and subsoil FC, EC1:5 and CEC. A comparison of σ2p,C of the traditional (seven pedoderm components) and DSM approach (k = 8) indicated that only topsoil EC1:5 and subsoil pH was better accounted for by the traditional approach, whereas topsoil clay content, and CEC and subsoil clay, EC1:5 and CEC were better resolved using the DSM approach. The produced DSM maps (e.g. k = 3, 6 and 8) also reflected the pedoderm components identified using the traditional approach. We concluded that the DSM maps with k = 8 classes reflected the soil profile classes identified within the pedoderms and that soil maps of similar accuracy could be developed from the EM data independently.

Spatial variability of soil properties and cereal yield in a cultivated field on sandy soil

Sandy soils are used in agriculture in different regions of the world. In Poland soils derived from sands occupy about 50% of agricultural area. Productivity of the soils depend on the soil properties that vary in the scale of field. This study aimed at determining and mapping the within-field variation of soil physical and chemical properties and grain yield of oats, rye, oats and triticale in 2001, 2002, 2003, 2015, respectively. The experiment was set up in a field (200×50m) on sandy soil in Trzebieszów (region Podlasie, Poland). The soil measurements included sand, silt, clay, and organic carbon (SOC) contents, cation exchange capacity (CEC), pH in the topsoil (0–10cm) and subsoil (30–40cm) layers in 2001, and water content and bulk density in the topsoil layer in spring and summer 2002–2003. The yields of oats were assessed in 2001 and 2003 and those of rye and triticale in 2002 and 2015, respectively. The soil properties and cereal yields were determined at 33–55 points in a grid evenly covering the whole field area. The results were analyzed using classic statistics and geostatistics by constructing semivariograms and 2D mapping by Inverse Distance Weighting (IDW). The cereal grain yields were significantly positively correlated with the topsoil water content (SWC) (r=0.295–0.711), clay content (r=0.081–0.174), and SOC in the subsoil (r=0.208–0.271) and CEC in both layers (r=0.123–0.298) and negatively correlated with bulk density (BD) (r=–0.065 to −0.279). The spatial dependence determined by the “nugget-to-sill” ratio was moderate or weak for the silt and clay content, CEC, and pH (29–79%) and strong for SOC, BD, SWC, and crop yield (0.2–13.2%). The effective range of the spatial dependence for all studied quantities varied from 9.9 to 120m. The cereal yields were positively and significantly correlated between all study years (r=0.141–0.734), which indicates inter-annual similarity in their spatial distribution. The 2D maps based on the IDW allowed assessing how gradual or sharp the changes in the studied quantities from one place to another are. Similar spatial patterns of the SWC, SOC and CEC, and crop yields were observed. This is of importance in precise and sustainable field management aimed at increasing and aligning spatial crop productivity of the studied low-productivity sandy soils that will have to be used in crop production due to the current shortage of land resources and food supplies on a global scale.

Effect of Surfactant Concentration on Thermal and Mechanical Properties of Poly(Butylene Succinate)/Organoclay Composites

ABSTRACTComposite materials consisting of poly(butylene succinate) (PBS) and montmorillonite (MMT), modified to various extents using trihexyltetradecylphosphonium chloride (THTDP) cations, were prepared using a simple melt intercalation technique. The surfactant contents were varied, i.e. 0.4, 0.6, 0.8, 1.0, and 1.2 times the cation exchange capacity (CEC) of the MMT. The intercalation of the surfactant molecules into MMT layers, confirmed by the increase in interlayer spacing and significant changes in the morphology of the modified MMT, facilitated the dispersion of the clay in the PBS matrix. The properties of the PBS-based composites were changed with increasing surfactant content. The melting and crystallization temperatures increased and the degree of crystallinity (χc) decreased. The storage modulus was significantly enhanced below the glass transition temperature (Tg), and Tg shifted to a higher temperature, with a maximum at a surfactant loading of 0.6 CEC. The mechanical properties, including tensile strength, flexural strength, flexural modulus and impact strength, increased and then decreased with surfactant loading, with the maximum observed also at a surfactant loading of 0.6 CEC. In conclusion, an ideal balance between thermal and mechanical properties can be obtained at a surfactant quantity equivalent to 0.6 times the clay CEC. Moreover, all the composites exhibited obvious improvement in thermal and mechanical properties as compared to those of neat PBS.