Smectitic Soils Research Articles

Effects of rainfall intensity and slope gradient on soil sealing and crusting, erosion, and phosphorus solubilizing bacteria

Soil erosion significantly affects various soil properties and processes, yet its impacts on soil microbial populations remains unclear. Understanding the effects of soil erosion on soil microbial properties enables the formulation of recommendations to protect soils and reduce their vulnerability. This study aimed to determine the effects of rainfall intensity and slope on soil crusting, erosion and bacterial communities in soils with various texture and mineralogy. Three kaolinitic soils with low to medium clay content (K1, K2, and K3) and three smectitic soils with high clay content (S1, S2, and S3) were subjected to simulated rainfall at three intensities (45, 70 and 100 mm/h) and two slopes (5° and 8°). Infiltration rate was measured using a graduated cylinder in 2-minute rotations of the simulator. Runoff and sediment yield were collected in a beaker. Crust strength was measured using a cone penetrometer, and its thickness was determined with a vernier caliper. Bacterial isolates were obtained by plating serial dilutions in nutrient agar and incubating them at 25°C for 24–48 h48 hous. The phosphate solubilising bacteria were then identified. The smectitic soils formed the strongest crusts with S2 exhibiting significantly (p < 0.05) higher crust strength (18.54 Kpa) at an intensity of 45 mm/h and slope of 8° On the other hand, soil K3 (kaolinitic) had the lowest crust strength (5.4 Kpa) at an intensity of 100 mm/h and slope of 8° Soil loss increased with higher rainfall intensity and steeper slopes for the kaolinitic soils with K1 being most erodible (468.2 kg/ha) at an intensity of 100 mm/h and slope of 8° The number of phosphate solubilising bacteria decreased with increasing rainfall intensity. Furthermore, this study revealed that soil properties played a more significant role in shaping bacterial composition and phosphate solubilisation than rainfall intensity alone. These findings highlight the complex interactions between soil erosion, bacterial communities, and soil properties, which are crucial for devising effective soil conservation strategies.

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.

Natural Processes and Anthropogenic Activity in the Indus River Sedimentary Environment in Pakistan: A Critical Review

The Indus River is Asia’s longest river, having its origin in the Tibet Mountain northwest of Pakistan. Routed from northern Gilgit and flowing to the plains, the river passes through several provinces and is connected by numerous small and large tributaries. The river was formed tectonically due to the collusion of the Indian and Eurasian plates, which is referred to as the Indus suture Plains zone (ISPZ). The geological setting of the study area is mainly composed of igneous and metamorphic rocks. The river passed through a variety of climatic zones and areas, although the predominant climate is subtropic arid and sub arid to subequatorial. Locally and globally, anthropogenic activities such as building, dams, and water canals for irrigation purposes, mining exploration, and industries and factories all affected the physical and chemical behaviors of the sediments in various rivers. The main effect of human activities is the reworking of weathered soil smectite, a chemical weathering indicator that rises in the offshore record about 5000 years ago. This material indicates increased transport of stronger chemically weathered material, which may result from agriculture-induced erosion of older soil. However, we also see evidence for the incision of large rivers into the floodplain, which is also driving the reworking of this type of material, so the signal may be a combination of the two. Sediments undergo significant changes in form and size due to clashing with one another in the high-charge river.

The Effects of Soil Solution Electrical Conductivity and Sodium Adsorption Ratio on Soil Liquid Limit and Soil Strength

ABSTRACT Irrigation water quality is a global agricultural management issue. High solution sodium adsorption ratio (SAR) and low electrical conductivity (EC) of irrigation waters decrease both hydraulic conductivity and aggregate stability. Little is known how solution EC and SAR affects soil mechanical properties. Three smectitic soils were treated with salt solutions made from sodium and calcium chloride that had SAR levels of 5 and 17 at solution levels between 5 and 40 millimoles charge per liter (mmolc L−1). Soil Atterberg limits were measured using Cassagrande method and penetration resistance was measured using a falling cone penetrometer. At 5 mmolc L −1, whole soil liquid limits increased from 46% to 50% on average when solution SAR levels increased from 5 to 17, whereas plastic limit did not change. When comparing the effect of increasing SAR from 5 to 17 at a salinity level of 5 mmolc L−1 on the Aberdeen soil, the water content increased at soil strengths between 0.5 and 100 kPa. Increasing soil solution SAR at low EC levels alters soil mechanical properties leading to undesirable soil qualities for agricultural production, specifically creating greater difficulty for seedling emergence and increasing the force required for tillage.

Mineralogical and physico-chemical characterization of gypsiferous semi-arid soils in the north of Urmia, Iran

Gypsiferous soils contain sufficient gypsum to influence soil physico-chemical, mineralogical, mechanical properties and geotechnical conditions and as a consequence, affect plant growth and crop production. So physico-chemical and mineralogical properties of 6 soil profiles located on the gypsiferous parent material with semi-arid climate in north of Urmia, West Azerbaijan province, Iran, were investigated. Based on standard methods, morphological, physico-chemical and mineralogical properties of these soils were determined. Soils with higher gypsum content had lighter color, lighter texture, lower values of organic carbon and cation exchange capacity and higher values of electrical conductivity. These parameters were reversely changed with decreasing gypsum content of soils. Semi-quantitative analysis of clay minerals indicated the presence of smectite, illite, chlorite, kaolinite and palygorskite were as major clay minerals with decreasing order from smectite to palygorskite. The origin of illite, chlorite and kaolinite were related to the inheritance from parent material. Smectite group of clay minerals has been resulted from three origins of inheritance from parent material, transformation of illite and palygorskite and neoformation, but the transformation and neoformation are the main pathways for its formation. Palygorskite has pedogenic origin and has been formed via neoformation. The comparison of clay mineralogy of soils with different gypsum values revealed the presence of higher smectites in soils with higher gypsum. Palygorskite was identified just in soils with higher gypsum. In soils with lower values of gypsum, illite and chlorite were the predominant clay minerals and palygorskite did not identified.

Assessment of soil response to exchangeable sodium percentage by consistence and water retention properties

The use of low-quality water for irrigation is expected to keep increasing worldwide, which increases the risk of soil degradation. The response of soil to irrigation waters with excessive sodium depends on the soil clay behavior. Soil physical properties that can distinguish smectitic soils from non-smectitic soils could identify soils that are sensitive to exchangeable sodium. This study explores the use of Atterberg limits, coefficient of linear extensibility (COLE) and soil water retention as possible properties to determine if a soil is sensitive to exchangeable sodium. Soils used were synthetic soils prepared from mixtures of silt and clay minerals, and six natural soils. Atterberg limits, COLE and soil water retention was measured at ESP values of 0, 50 and 100% on these soils. Multiple linear regression functions were developed to predict soil liquid limit, plasticity index, COLE, and soil water retention at −336 cm H2O. The liquid limit, and COLE increased as the amount of sodium-saturated smectite increased in the synthetic soils. The liquid limit, COLE and water retention at matric potentials greater than −336 cm of H2O increased on smectite clay dominant soils when elevated ESP was combined with low salinity. The liquid limit increased from 49 to 67 on average and −336 H2O water content increased from 38 to 70% on average between 0 and 100% ESP treatments on the four smectitic soils. On a kaolinitic soil liquid limit decreased from 56.1 to 51.8 and −336 H2O water content increased from 33.7 to 35.9% between the ESP 0 and 100% treatment. Liquid limit increased from 188 to 679 and COLE increased from 0.47 to 1.19 mm mm−1 between calcium smectite (fullers earth) and sodium smectite (Wyoming bentonite), whereas liquid limit decreased from 56 to 39 and COLE decreased from 0.195 to 0.104 mm mm−1 between calcium and sodium saturated kaolinite. Plasticity index increased by 75% between the ESP 0 and ESP 100 treatments on the smectitic soils, whereas there was a 260% increase in plasticity index between fullers earth and bentonite. The root mean squared error that liquid limit could be predicted with was 3.3 plastic limit was 2.4, COLE was 0.036 mm mm−1, and 1/3rd bar water content was 2.2 × 10−3 g g−1. Smectitic soils had increases in soil swelling related properties, whereas non-smectitic clay soils had no changes in swelling related properties from ESP. Liquid limit and water retention at water potentials of −1/10th and −1/3rd bar were the properties that best distinguished soils that respond to ESP from soils that do not respond to ESP. Soil consistence properties and water retention can determine soils that contain smectite clay which is the clay mineral that is most sensitive to soil ESP.

Polyacrylamide dissolved in low-quality water effects on structure stability of soils varying in texture and clay type

ABSTRACT Efficacy of polyacrylamide (PAM), a water-soluble soil conditioner, prepared with poor-quality water (low salinity, higher sodicity) commonly available to farm managers, is unknown. We studied the effects of treating aggregates of four soils with predominant smectitic or kaolinitic clay mineralogy with PAM solution prepared with poor-quality water (low salinity and high sodicity). Impact of PAM on pore size distribution (PSD) and structure stability of the soils and the relations between the stability indices obtained were studied from water retention curves derived at low suction (0–50 hPa). The retention curves were characterized by a modified van Genuchten model that yields (i) the model parameters α and n and (ii) a soil structure index (SI). Applying PAM modified the water retention curve shape, mostly in the smectite soils, and increased α and improved SI up to 3.3 and 1.7 times in the smectitic and kaolinitic soils, respectively, relative to the control. An observed exponential relationship between soil SI and parameter ɑ allowed predicting the effects of PAM addition on soil structure stability. The noted improvement in structure stability was comparable with results for conditions where PAM solution was prepared with good-quality water. Abbreviations: PAM, polyacrylamide; SAR, sodium adsorption ratio; EC, electrical conductivity; HEMC, high-energy moisture characteristic; VDP, volume of drainable pores; MS, modal suction; SI, structural index; PSD, pore size distribution.

Influence of exchangeable sodium and clay mineralogy on soil water retention and hydraulic conductivity

Soil hydraulic properties are important for water management in salt and sodium (Na) affected soils. The soil saturated hydraulic conductivity (K_sat) has been found to decrease when high soil solution Na adsorption ratio (SAR) is coupled with low solution electrical conductivity (EC). Soil clay type plays an important role in changes to soil K_sat when the soil solution composition has a high SAR and low EC. Little is known about how soil water retention changes from solution EC and SAR. The objective of this study was to determine the impact of a range of solution EC and SAR values on soil K_sat, and water retention for soils containing swelling and nonswelling clay minerals. The soil K_sat and water retention were measured on four smectitic soils, a kaolinitic soil, and an illitic soil. Smectite swelling caused large changes in soil hydraulic properties in smectitic soils at high exchangeable Na percentage (ESP) and low EC levels, whereas there was a reduced effect on soils with little smectite clay. Increasing soil solution ESP and decreasing EC level caused the K_sat to decrease and the water content at a given pressure head to increase on soils that contained smectite. A narrower range of EC and SAR of waters suitable for use on smectitic soils are required to prevent changes in soil water flow rates and soil water retention.

Improvement in the rheological and mechanical properties of clay mortar after adding Ceratonia Siliqua L. extracts

In this study we have investigated the use of one of the components of the carob tree, Ceratonia Siliqua L. polyphenols, as an additive to improve the rheological properties of clay mortars used for sustainable construction. To obtain comparable results, soils with different clay bases have been used as raw materials. The most relevant results were the increased fluidity of the material and, consequently, a reduction in mixing water, especially in kaolinite soils with a decrease of 57.16 w% and in smectitic soils with 66.25 w%. Significant improvements in the mechanical behaviour of the mortars supplemented with the polyphenols derived from carob were observed.

Comparison of HCl and H2SO4 for the acid activation of a cameroonian smectite soil clay: palm oil discolouration and landfill leachate treatment

Vertisols occupy approximately 1,200,000 ha in Northern Cameroon. Their richness in smectites allows for the production of “bleaching earths” necessary for refining palm oil, and their effluent is used for leachate treatment. In the present work, two mineral acids (HCl and H2SO4) were compared, and the most efficient acid with the lowest cost was determined for use in industrial applications. Under similar experimental conditions (ratio of acid solution/clay mass = 5/1, temperature = 97 °C, stirring time = 4 h), the quantity of cations (Fe2+, Fe3+, Al3+) solubilised during acid activation, palm oil discolouration rate by each activated sample and the financial cost of 5 L of acid solution that is required for the acid activation of one kilogram of smectite clay were compared. It was found that 2N H2SO4 was more efficient than 1N HCl and 1N H2SO4, considering palm oil bleaching efficiency and cost. The filtrate collected after the acid activation of vertisols was rich in H+ (2.04.10−1M), Fe2+ (2.8.10−3M), Fe3+ (4.2.10−2M) and Al3+ (9.2.10−2M) ions. One gram of smectite clay material produced 9 mL of this filtrate that was used for the treatment of leachate from a controlled landfill. The leachate colour decreased from 4262 to 285 PtCo units, while the corresponding chemical oxygen demand (COD) decreased from 802 to 128 mg/L. Thus, the most effective acid for industrial bleaching earth production from vertisol is 2N H2SO4 acid.

Effect of Irrigation Water pH on Saturated Hydraulic Conductivity and Electrokinetic Properties of Acidic, Neutral, and Alkaline Soils

The demand for the use of marginal‐quality water as an irrigation resource is increasing in arid and semiarid region lands due to the freshwater shortage. Marginal waters usually have high salinity and high alkalinity and may contain high proportions of ions such as sodium. This study investigated the impact of irrigation water pH on saturated hydraulic conductivity (Ks), cation exchange capacity, net particle charge, and dispersivity of soils. Nine soils with differing pH, alkalinity, clay content, and mineralogy were used in leaching column experiments, with solutions of varying sodium adsorption ratio (20 and 40), electrical conductivity (0.8, 1.5, 2.5, 5, 10, 25, and 50 dS m−1), and pH (6, 7, 8, and 9). The desired pH was achieved by adjusting the HCO3−/Cl− ratio and CO2 partial pressure using CO2 gas with 99.9% purity. Results showed that the increase of solution pH causes an increase in net negative charges on clay particles, resulting in higher exchangeable cations, negative ζ‐potential, and clay dispersion and movement of dislodged particles into pore spaces, resulting in Ks reduction. This effect was more evident for acidic and low‐clay‐content soils. The Ks reduction in relation to pH was less for smectitic and high clay content soil than for kaolinite dominant soils for all concentrations, suggesting resiliency of the smectitic soils under irrigation water with high pH. Results reinforce that it is essential to consider the original pH, clay content, and mineral of the soil and the pH, electrical conductivity, and sodium adsorption ratio of the irrigation water to accurately predict the Ks reduction of the soil.

PHOSPHORUS SORPTION KINETIC ON ACID UPLAND SMECTITIC SOIL AMENDED WITH CALCIUM CARBONATE AND CALCIUM SILICATE

Acid upland smectitic soil is identified by high amount of exchangeable Al due to the weathering of aluminum (Al) octahedral layer by H+ saturation and by very low phosphorus (P) status. Calcium carbonate (CaCO3) and calcium silicate (CaSiO3) were commonly used to decrease exchangeable Al and increase soil pH. Laboratory experiments were conducted with clayey smectitic Typic Paleudults from Gajrug region, West Java. The CaCO3 and CaSiO3 were added at rates to replace 0, 1.5 or 3 times of exchangeable Al. After one month of incubation, P sorption kinetic experiments were conducted. The changes in some chemical properties after one month incubation showed that both CaCO3 and CaSiO3 increased the soil pH, exchangeable Ca, and base saturation but did not increase the cation exchange capacity. The results of the experiment showed that both CaCO3 and CaSiO3 decreased the rate constant value of first order kinetic equation (k) and the P sorbed maximum (a) at given amount of added P compared to Control.The CaCO3 was better than CaSiO3 in decreasing k values and on the contrary for a values. The decrease in P maximum sorption and the rate constant of the soil amended with CaSiO3 and CaCO3 due to occupation of P sorption sites by silicates and hydroxyl ions. The CaCO3with the rate to replace 1.5 x exchangeable Al was recommended to decrease the rate constant of P sorption. However, the CaSiO3 at the rate to replace 3 x exchangeable Al was recommended to decrease the maximum P sorption.

Measured saline and sodic solutions effects on soil saturated hydraulic conductivity, electrical conductivity and sodium adsorption ratio

Hydraulic conductivity is important in the transport of water and salts in salt affected soils. The objective of this study was to determine how saturation of soil columns with saline and sodic solutions changes soil saturated hydraulic conductivity (Ksat) and subsequent salt leaching on a variety of soil textures and smectite clay content. Soil columns were capillary wetted with solutions of varying electrical conductivity (EC) and sodium adsorption ratio (SAR). Ksat was measured by infiltrating deionized water at the soil surface. Ksat as a function of leachate pore volume was fit with an exponential decay equation and a pedotransfer function was created to predict the decay coefficients. Higher salt contents in waters were more successful at increasing soil SAR as compared to low salt content waters. The pedotransfer functions performed similar to the McNeal and Simunek and Suarez models to predict Ksat change due to solution composition without the need of X-ray diffraction of the soil clay fraction. Soils with a greater clay content and specifically smectite clay content have larger changes in saturated water flow rates whether from one time wetting or under long term use of irrigation waters at high EC and Low SAR. High clay smectitic soils require careful management when they are saline-sodic and have a smaller range of safe irrigation waters to prevent reduction in hydraulic conductivity from SAR.

Atterberg limits and shrink/swell capacity of soil as indicators for sodium sensitivity within a gradient of soil exchangeable sodium percentage and salinity

Soil sodification and salinization present a global soil degradation risk to agricultural production since they affect soil hydraulic properties. Soils containing smectite clays have been found to be most sensitive to sodicity although little research exists directly relating sodicity to clay swelling under varying levels of salinity and Exchangeable Sodium Percentage (ESP). The goal of this study is to determine whether soil swelling related measurements can be a proxy to determine soil sensitivity to exchangeable sodium. This study examined the response of three smectitic soils treated with salt solutions having concentrations ranging between 5 and 40 mmolc dm−3 and ESP levels between 0 and 50% to create differing degrees of sodicity. Whole soil Atterberg limits and the coefficient of linear extensibility (COLE) were measured prior to and after treatments. Liquid limit, plasticity index and the coefficient of linear extensibility increased for all three soils after treatment with a salt concentration of 5 mmolc dm−3 at an ESP of 25 and 50% and 10 mmolc dm−3 at an ESP of 50%. Comparing liquid limit of low salinity treatment at 50% ESP to low salinity 0% ESP revealed the presence of swelling smectite clay and the sensitivity of the soils to sodicity and a soil measurement to identify soil sodicity risk.

Improved estimation of clay content from water content for soils rich in smectite and kaolinite

Standard measurement methods for soil clay content, including the hydrometer and pipette methods, are laborious and difficult to repeat. This has motivated the application of proxy methods such as estimation of clay content from soil water vapor sorption isotherms. Previous studies have revealed that vapor sorption-based clay estimates are inaccurate for soils dominated by swelling or highly weathered non-swelling clays such as kaolinite. In this study, we evaluate an existing vapor sorption-based clay estimation model for soils dominated by either illite (IL), smectite (SM), or kaolinite (KA) clay minerals, and propose modifications to account for high SM and KA contents. Compared to the pipette method, the clay content obtained from the existing water sorption model at 50% relative humidity (RH) was accurate for the IL samples, but significantly overestimated (RMSE = 23.7%; ME = 19.7%) or underestimated (RMSE = 28.8%; ME = −17.0%) clay content for SM and KA rich soils, respectively. The proposed modification involves correcting the estimated clay content with a “slope factor”, S for RH values ranging from 30 to 90% for both adsorption and desorption. For SM samples, S averaged 0.76 and 0.72 for adsorption and desorption, respectively, and for KA samples, S ranged from 2.26 to 1.19 and followed a polynomial relationship with RH. Comparison of the estimated clay content from the modified models showed markedly improved estimation of the measured clay content (for RH of 90%, RMSE = 8.0%; ME = 2.6% for SM samples and RMSE = 9.6%; ME = −5.7% for KA samples).

Shrinkage limit test results and interpretation for clay soils

The shrinkage limit is one of the Atterberg limits and is a fundamental geotechnical parameter used to assess the settlement of engineering soils containing clays, yet is rarely tested for as part of ground investigation. This paper describes shrinkage limit test results on a variety of soils from Britain and overseas obtained using an improved laboratory testing procedure developed at the British Geological Survey. The co-relationships with the other Atterberg limits and with density are explored. In particular, the coincidence of the shrinkage limit with the water content at the peak bulk density achieved in the test is examined. The shrinkage behaviour for undisturbed and remoulded states and a three-way relationship between water content, density and suction are demonstrated. Some tropical residual and highly smectitic soils show a very wide range of shrinkage behaviour, albeit for a small dataset, when compared with the larger dataset of temperate soils tested. Consideration is given to limitations of the new and existing test methods.

The Role of Clay Swelling and Mineral Neoformation in the Stabilization of High Plasticity Soils Treated with the Fly Ash- and Metakaolin-Based Geopolymers

In the southern U.S. states, expansive soils are frequently encountered, presenting an important hazard in geotechnical engineering. This research relies on mineralogical and geochemical clues to explain the swelling behavior of smectite-rich, high-plasticity soils, documented in a series of geomechanical swelling tests that were performed on the soils stabilized with the metakaolin (MKG) and fly ash (FAG) based geopolymers. These geopolymers were mixed with the soil at several concentration levels. The lowest swelling percentage was shown to correspond to the sample stabilized with 12% FAG and was attributed to the neoformation of calcium silicate hydrates that acted as a cementitious material, preventing the soil from expanding by occupying the pore space, thus binding the clay particles together. Conversely, the 12% MKG-stabilized soil exhibited enormous expansion, which was explained by montmorillonite swelling to the point that it gradually began to lose its structural periodicity. The relatively high abundance of the newly formed feldspathoids in MKG-treated samples is believed to have greatly contributed to the overall soil expansion. Finally, the cation exchange capacity tests showed that the percentage of Na+ and Ca2+, as well as the pH value, exercised strong control on the swelling behavior of smectitic soils.

Soil Shrinkage Characteristics as Affected by Solution Composition and Mineral Contents

ABSTRACTSoil-shrinkage characteristics affect fluid transport and soil mechanical properties, with broad implications for environmental flows, crop production, and civil engineering designs. We quantified mild-saline-solutions effects on soil shrinkage curves and developed pedotransfer functions to predict curve parameters. Seven soil and soil mixes were equilibrated with solutions of 0.5-to-8 dS m−1 and 0-to-20 sodium adsorption ratios (SAR). Saturated paste rods were dried; water contents and isotropic shrinkage measured. Texture affected shape-forming factors when clay and smectite contents were >260 and 140 g kg−1, respectively. Solutions ≥2 dS m−1 affected the coefficient of linear extensibility for smectitic soils containing clay ≥300 g kg−1. Solution SAR affected only the highest clay content (530 g kg−1) and mixed mineralogy soils. However, the solution salinity levels were not high enough to affect shape factors of the shrinkage curves. Pedotransfer functions successfully described soil shrinkage with root-mean-squared-errors 1 to 4 magnitudes lower than the highest measured values.

Geotechnical applications of chemically enhanced drainage

SummaryThe paper explores application of the engineered increase in soil permeability, achieved using reaction of guanidinium solutions with smectite soils, to geotechnical problems. The comparison between the finite element analysis of the enhanced permeability model for axisymmetric conditions and a simplified analytical solution demonstrates the importance of accounting for diffusive and dispersive fluxes. In order to illustrate possible practical application of the proposed soil improvement technique, two geotechnical examples have been numerically explored: improving performance of a ground water well and the stabilization of a slope by chemically enhanced drainage. For the well application, it has been demonstrated that for a relatively small degree of treatment, the power consumption can be reduced to a half, compared with the non‐treated soil. For the slope stability application, the water table downstream of the drain can be significantly lowered using moderate pump/collector pressures at the centre of the drain, causing a higher increase in the factor of safety for a larger area subjected to the chemically enhanced drainage. The particularly promising result is that in both applications the largest gain in the well/drain efficiency has been observed for smaller chemically enhanced areas, where a short duration of treatment and small amounts of chemicals decrease the power consumption and increase the safety factor at the highest rate. Copyright © 2017 John Wiley &amp; Sons, Ltd.

Relationship between soil clay mineralogy and carbon protection capacity as influenced by temperature and moisture

Environmental conditions like temperature and moisture could affect the carbon protection capacity of various clay types in soils. Using dominantly kaolinitic-illitic, smectitic and allophanic soils, we conducted systematic incubation experiments over 42 days at different temperatures (4, 22 and 37 °C) and moisture contents (30, 60 and 90% of water holding capacity (available water)). The basal respiration was monitored to study the relative effect of moisture contents and temperature on the carbon protection capacities and mechanisms of the three clay types. The results indicated that carbon decomposition increased with increasing moisture and temperature. A two-component quadratic equation could explain the carbon mineralisation process. The highest C respiration was observed at 37 °C with a 60% moisture level in each of the soil types. Under these conditions, the smectitic soil recorded the highest carbon decomposition followed by the kaolinitic-illitic and allophanic soils. The study of the priming effect using 14C labelled malic acid confirmed the trend of the bulk respiration results. The allophanic soil showed the lowest amount of carbon mineralisation under all experimental conditions. A strong inverse correlation (R2 = 0.90 at p < 0.05) was observed between CO2 emission rate and total sesquioxides (Fe and Al oxides) content. As evidenced by the pore size distribution, micromorphologies and thermogravimetric analyses, the microporous structure and microaggregate formation in the allophanic soil enhanced carbon sequestration. This study indicated that soil carbon stabilisation was related more to the sesquioxides content than to the clay types or their relative specific surface areas.