Column Leaching Experiments Research Articles

Hollow microspheres of layered double hydroxides through surfactant-free method enhanced heavy metals removal from soil

A three-dimensional MgAl layered double hydroxides hollow microsphere (HMS-LDH) is fabricated by surfactant-free method. The microstructure and the formation mechanism of HMS-LDH are investigated by XRD (X-ray diffraction), SEM (Scanning Electron Microscope), EDS (Energy dispersive Spectrometer) and XPS (X-ray photoelectron spectrometer). The morphology of LDHs could be varied by changing the ratio of metal cations to urea. The adsorption properties of HMS-LDH for heavy metals from soil are investigated. The results of experiments demonstrates that the adsorption kinetics of Cu(Ⅱ), Pb(Ⅱ), As(Ⅴ), Cr(Ⅵ) are in good agreement with the pseudo-second-order kinetic and intraparticle diffusion model. The adsorption isotherm data of Cu(Ⅱ)/Pb(Ⅱ) is accordance with the Langmuir-Freundlich model, while the equilibrium adsorption of As(Ⅴ)/Cr(Ⅵ) follow the Generalized-Langmuir isotherm model well. Site energy distribution theory denotes the hollow microsphere structure increases the adsorption sites of heavy metals, which is conducive to the adsorption process. The different mechanisms of precipitation for Cu(Ⅱ)/Pb(Ⅱ) removal and interlayer adsorption for As(Ⅴ)/Cr(Ⅵ) removal are proposed. The effects of coexisting cations and column leaching experiments on the performance evaluation are also investigated, which indicate most the ions have no effect on the adsorption of Cu (Ⅱ)/Pb(Ⅱ) and As(Ⅴ)/Cr(Ⅵ). This work proposes a simple approach to prepare LDHs hollow microspheres and demonstrates their excellent properties for the remediation of heavy metal polluted soil.

Sulfur/zinc co-doped biochar for stabilization remediation of mercury-contaminated soil: Performance, mechanism and ecological risk

In this study, a novel sulfur/zinc co-doped biochar (SZ-BC) stabilizer was successfully developed for the remediation of mercury-contaminated soil. Results from SEM, TEM, FTIR and XRD revealed that biochar (BC) was successfully modified by sulfur and zinc. In the batch adsorption experiments, the sulfur-zinc co-pyrolysis biochar displayed excellent Hg(II) adsorption performance, with the maximum adsorption capacity of SZ-BC (261.074 mg/g) being approximately 16.5 times that of BC (15.855 mg/g). Laboratory-scale static incubation, column leaching, and plant pot experiments were conducted using biochar-based materials. At an additional dosage of 5 % mass ratio, the SZ-BC exhibits the most effective stabilization of mercury in soil, leading to a significant reduction in leaching loss compared to the control group (CK) by 51.30 %. Following 4 weeks of incubation and 2 weeks of leaching with SZ-BC, the residual mercury in the soil increased by 27.84 %. As a result, potential ecological risk index of mercury decreased by 92 % compared to the CK group. In the pot experiment, SZ-BC significantly enhanced the growth of Chinese cabbage, with biomass and root dry weight reaching 3.20 and 2.80 times that of the CK group, respectively. Additionally, the Translocation Factor (TF) and Bioconcentration Factor (BF) were reduced by 44.86 % and 74.43 %, respectively, in the SZ-BC group compared to the CK group. Moreover, SZ-BC can effectively improve enzyme activities and increase microbial communities in mercury-contaminated soils. The mechanisms of adsorption and stabilization were elucidated through electrostatic adsorption, ion exchange, surface complexation, and precipitation. These findings provide a potentially effective material for stabilizing soils contaminated with mercury.

Nitrogen leaching mitigation by tithonia biochar (Tithochar) in urea fertilizer treated sandy soil

Abstract Nitrogenous fertilizer drift from farmlands accelerates nitrogen loads in groundwaters. Biochar potential to mitigate nitrogen leaching in urea treated sandy soil was monitored in a four weeks screenhouse leaching column experiment. The trial was a factorial combination of two biochar types (B1 and B2 applied at 5 t/ha) and two urea treatments (with urea at 120 kg/ha and without urea) laid in completely randomized design with three replications. Control that received neither urea nor biochar was compared. Four weekly leaching events were conducted in each leaching column containing 300 g soil amended with appropriate treatments. Amaranthus hybridus was the test crop. The NH4-N and NO3-N leached were generally highest during the week 2 leaching event such that total NO3-N leached was 427.3 % higher than total NH4-N leached with highest contributions from sole urea treatment. Biochar pretreatment reduced total N leached by 9.5 (B1) and 26.8 % (B2) relative to sole urea. Percentage of N added lost to leaching was highest (34.1 %) in sole urea treatment with B1 and B2 pretreatment reducing the value by 54.5 and 46.9 % respectively. Correlation analysis revealed electrical conductivity of the leachate and soil as dominant indicators for N leached in the soil studied.

ZnCl2 and thiourea co-modified biochar for effectively removing quinclorac in water and soil: Mechanism and alleviating its phytotoxicity on tobacco plants

The overuse of herbicide may cause pollution in water and soil environment, affecting the growth of crops. And how to reduce herbicide residues has aroused extensive attention. In this work, a novel modified biochar (Zn/SN-BC) was prepared with reed straw as raw material, ZnCl2 and thiourea as modifiers to remove quinclorac (QC) residues in water and soil. Compared with primitive biochar, Zn/SN-BC, benefiting from higher specific surface area (766.5 m2·g−1), improved pore characteristics and abundant reactive sites (−C = O, −COOR, −C-N, −C-S, ZnS, etc), showed excellent adsorption capacity towards QC (235.9 mg·g−1), which was much higher than others reported before. According to the characterization results, it was revealed that Zn/SN-BC adsorbed QC through pore filling, hydrogen bonding, π-π conjunction, electrostatic attractions and other chemical interactions. The column leaching and pot experiments demonstrated that Zn/SN-BC could reduce QC leaching and bioavailability in soil, and effectively alleviate its phytotoxicity on tobacco plants. This study gives a new insight into the application of biochar-based materials for the treatment of herbicide residues in agricultural environments.

Granulated fertilizers are more efficient in reducing potassium leaching losses than combining biosolids with inorganic sources

ABSTRACT Widespread use of soluble mineral fertilizers derived from non-renewable sources has raised concerns about environmental impacts, energy expenditures, and sustainability. Combining biosolid and mineral sources of phosphorus and potassium to produce organomineral fertilizers (OMF) can be used as an alternative nutrient source while reducing the environmental impact of sewage residues. As this approach simultaneously provides nutrients and incorporates organic matter, we hypothesized the presence of an organic source (biosolid) granulated with mineral sources of potassium (K) and phosphorus (P) would reduce leaching due to the benefits of the organic source and the slower release caused by granulation. Our goal was to evaluate the effect of different OMFs on the leaching losses of nutrients. Two forms of isolated N, P, and K sources (granulated and non-granulated), five OMFs with different NPK proportions (1-2-0, 1-4-0, 1-0-2, 1-2-2, 1-2-4), and a control (unfertilized) were evaluated over ten weeks in a leaching column experiment. Non-granulated potassium sulfate exhibited the highest K leaching and did not differ from OMFs with K in their formulation (granulated PS, 1-0-2, 1-2-2, and 1-4-2). Planned contrasts showed that granulation was particularly effective at reducing K leaching, resulting in a 70 % reduction compared to non-granulated PS. While formulation and granulation showed a trend of potential benefits in reducing N-(NO 3 - + NO 2 - ) leaching, the effect was not statistically significant. Interaction between fertilizer treatments and leaching events was marginally significant for NH 4 + leaching, indicating temporal variations of OMFs in nutrient dynamics may be influenced by mineralization. As granulation modulated how OMFs affected nutrient leaching dynamics, this highlights the importance of the physical characteristics of fertilizers for effective nutrient management.

Environmental risk of ion-absorbed rare earth ores: concentration of leaching agent and fractionation of Pb.

Rare earth (RE) is an important strategic resource; however, there has been a growing concern about the environmental problems caused by RE mining, such as ammonia nitrogen pollution and heavy metal pollution. There is a limited research about the behavior of leaching agents and the fractionation of RE and heavy metal during the mining process for ion adsorption of rare earth ore (IRE-ore) in the previously available papers. In this study, (NH4)2SO4 solution, which commonly used in the production of mining IRE-ore, was used as a leaching agent. The adsorption behavior of ore soils on ammonium ions was explored by batch experiments. The adsorption process of IRE-ore on ammonium ions followed a pseudo-second-order equation and was controlled by the kinetics of surface adsorption and intra-particle diffusion; the ammonium ion adsorption isotherm conformed to the Freundlich isotherm equilibrium equation, and the higher concentration advantage made the ore soils possess a higher adsorption capacity of ammonium ion. In addition, the fractionation characteristics of lanthanum (La), cerium (Ce), and lead (Pb) in the ore soil during the leaching process were simulated based on the batch and column leaching experiments. The results demonstrated that the exchangeable states of La and Ce in IRE-ore were high, and the exchangeable, carbonate-bound La and Ce were almost all leached out by (NH4)2SO4 leaching agent, while the most of exchangeable Pb flowed out along with leaching agent, and a small amount of leached Pb in the ore soil was converted to iron and manganese oxide-bound Pb and enriched in the direction of migration of the leaching solution, and when the environment (e.g., pH and Eh) changed, this part of Pb may be re-activated. Our research might serve as crucial baseline knowledge for the adsorption of ammonium ions by ore soils, and provide a data reference for reducing the use of leaching agents and developing sustainable technologies for green mining of ion-adsorption RE ores.

Leaching of soil legacy nitrogen in intact soil columns and significance of soil macropore structure

Excessive application of chemical fertilizers accumulates nitrogen in soil (soil legacy nitrogen), and its release has a long-term impact on environmental quality. The information regarding leaching of soil legacy nitrogen and role of soil pore structure is scarce. Fifteen undisturbed soil cores with a depth of ~200 mm were collected from five paddy fields in a subtropical area of China, and soil pore structure was characterized with X-ray computed tomography. The batch leaching column experiments were conducted to investigate the nitrogen leaching from the soil cores. In the leachate, inorganic nitrogen (NO3−–N and NH4+–N) accounted for 73–85 % of total dissolved nitrogen (TDN), which showed small variations among the five sampling sites. The NO3−–N, NH4+–N and TDN concentrations in the leachate over the number of leaching times could be well fitted with the Gaussian, exponential or linear models, suggesting that different nitrogen forms showed variable leaching dynamics. NO3−–N and TDN leaching losses continued to increase with the number of leaching times, whereas NH4+–N leaching from the soil had a threshold value. Combination of changes in soil nitrogen content after leaching, the lagging effect of soil legacy nitrogen may be partly attributed to the continuous transformation of NH4+–N and organic nitrogen into NO3−–N in the soils. Besides the nitrogen content in the soil, the most important factor of soil pore structure controlling NO3−–N and TDN leaching loss was the fractal dimension; NH4+–N was mainly controlled by connectivity. The present study highlighted the importance of soil pore structure and nitrogen format transformation in the leaching of soil legacy nitrogen.

Effect of particle size on the leaching of a weathered crust elution-deposited rare earth ore

Weathered crust elution-deposited rare earth ore is a typical porous medium, and the size of ore particles plays a crucial role in solution flow and rare earth ion transport. Ore particles with different sizes were obtained, and column leaching experiments were performed to study their seepage and leaching characteristics. Subsequently, the mechanisms underlying the effect of particle size on leaching were analysed. The results showed that the maximum concentration of the rare earth leachate and the penetration time of the samples decreased with the increase of the ore particle size, and the flow rate of the leachate exhibited an opposite trend. The breakthrough curves of the samples exhibited two forms: monotonically decreasing and parabolic. When the leaching solution was sufficient, the leaching efficiencies of the samples comprising ore particles larger than 5 mm and smaller than 0.075 mm were 75% and 95%, respectively, whereas the leaching efficiencies of the other samples reached 100%. The influencing mechanism showed that when ore particles are large, the pores among the particles lead to a low leaching efficiency. On the contrary, when the ore particles are small, the re-adsorption of rare earth ions to the surface of the ore particles can be easily promoted under the combined action of poor permeability, the high clay mineral content, the large specific surface area, the imbalance of the salt solution concentration between the ore and the solution and the weakly acidic leaching environment, resulting in a low leaching efficiency. Furthermore, the micromorphology of ore particles with a small size showed a rough surface, and the structure destroyed by leaching was unconducive to the flow rate of the solution in the orebody.

Effective adsorption of heavy metals on layered double hydroxides modify through dithiocarbamate prepared by CS2 and different molecular weight of polyethyleneimine

Dithiocarbamate (DTC) with different molecular weight were prepared to modify Mg-Al layered double hydroxides (LDH-DTC) for adsorbing Cu(II), Pb(Ⅱ), Zn(Ⅱ), Cd(Ⅱ) from contaminated soil. The structural and morphology characterization indicated that DTC was wrapped outsides LDHs layer, and the coating layer became thicker with the increase of DTC molecular weight. The adsorption performance of LDH-DTC for heavy metal was investigated and adsorption kinetics was well followed pseudo-second-order and intraparticle diffusion model. The data of adsorption isotherm showed that the adsorption of Cu/Pb fitted Freundlich model, while the adsorption process of Zn/Cd fitted Langmuir model. Additionally, adsorption mechanism of LDH-DTC for Cu(II)/Pb(Ⅱ)/Zn(Ⅱ)/Cd(Ⅱ) with different concentration was explored. As the concentration of heavy metals was low, heavy metals first react with DTC encapsulated outside LDHs. With the increase of concentration, adsorption site of DTC was completely occupied, Cu(Ⅱ)/Pb(Ⅱ) began to react with the exposed LDHs layer to form precipitation, and Zn(Ⅱ)/Cd(Ⅱ) were immobilized on the LDHs layer by isomorphous replacement. The effects of pH, coexistence ions, heavy metal leaching, reuse, column leaching, and metal morphology classification experiments were also conducted, and these results revealed a high stability and favorable interception. The excellent adsorption performance suggested LDHs modified by DTC offered a promising method to immobilize heavy metals from soil and into practical application.

Potassium assisted pyrolysis of Chinese Baijiu distillers' grains to prepare biochar as controlled-release K fertilizer

A novel K-loaded biochar as controlled-release K fertilizer was prepared through K assisted pyrolysis of distillers' grains (DGs, typical solid-byproducts of Chinese Baijiu) under different atmospheres (N2 and CO2) and temperatures (400 and 800 °C). The fabricated DGs-based biochar exhibited high K loading (200.20–232.33 mg/g), and the release kinetics and column leaching experiments suggested that K-loaded biochar exhibited excellent controlled release performance in a long term. Compared with other biochar, the K-loaded biochar prepared at CO2 and 400 °C has lower cumulative release ratio of 82.35 %, and could retain the durative K release at ~0.5 % for 25 d. The release kinetics suggested that the K release behavior was dominated by dissolution, electrostatic attraction, adsorption, confinement effect, and chemical interaction. Furthermore, pot experiments revealed that K-loaded biochar could promote the growth of Komatsuna, in which the fresh weight and chlorophyll relative content of Komatsuna cultivated with biochar prepared at CO2 and 400 °C reached 0.146 g and 41.95 after 25 d growth, respectively. The above results suggested that the K-loaded biochar exhibited excellent utilization potential as a controlled-release K fertilizer, facilitating the sustainable development and resource valorization of Baijiu industry.

Slow release fertilizers based on polyphosphate/montmorillonite nanocomposites for improving crop yield

Nanocomposites are promising materials for the development of novel and environmentally friendly fertilizers that can delay the release of nutrients. In this study, a novel high-strength spherical nanocomposite fertilizer was prepared via agglomeration and granulation using montmorillonite, urea phosphate, urea, and potassium chloride as raw materials. The properties and morphology of the prepared fertilizer were characterized by Fourier Transform Tnfrared Spectroscopy (FT-IR), X-ray Diffraction (XRD), Scanning Electron Microscope (SEM), Transmission Electron Microscope (TEM), Thermogravimetric Analysis (TGA) and X-ray Computed Tomography (XCT) techniques. FT-IR analysis identified the formation of polyphosphate in fertilizer and hydrogen bonds between polyphosphate and montmorillonite. XRD analysis showed increased montmorillonite interlayer spacing and confirmed the formation of polyphosphate-montmorillonite nanocomposites. The effects of raw material mass ratio, reaction time, and reaction temperature on the strength and fluidity of nanocomposite fertilizer granules and the optimum preparation process was obtained by the response surface method (RSM-CCD). The optimum preparation process was obtained as follows: reaction temperature, 103 °C; reaction time, 237 min; and mass ratio, 1:1:0.93:1 (urea phosphate: urea: potassium chloride: montmorillonite). Under these optimum conditions, the particle hardness and angle of repose of the prepared fertilizer were 64.75 ± 0.48 N and 30.84 ± 0.95°. Nutrient release and agronomic effectiveness of the fertilizer was evaluated using column leaching and pot experiments, respectively. The column leaching experiment and XCT analysis demonstrated that the nanocomposite structure was responsible for the slow nutrient release. The pot experiment showed that compared with the traditional fertilizer, the soil nitrate and available phosphorus was increased by 28.02% and 43.45%, respectively, and the maize yield was increased by 24.27% with the application of prepared fertilizer. This work provides support for the preparation of high-strength spherical nanocomposite fertilizers and their large-scale applications in modern mechanical agriculture.

Organic Amendments Addition on Altering the Sorption, Vertical Movement and Leaching Behavior of Herbicides in Soil

Herbicides are applied indiscriminately to achieve maximum weed control in agricultural production which might contaminate the food chain through the bio-augmentation of residue concentration in soil. One of the management suggested to overcome the herbicides contamination is treating with various organic amendments. Hence the laboratory column leaching and sorption experiments were conducted in Tamil Nadu Agricultural University (TNAU), Coimbatore to investigate the leaching behavior of herbicides viz., pendimethalin, atrazine and imazethapyr in soil as influenced by various organic amendments applied @ 5t/ha viz., FYM, vermicompost, composted coir pith, maize crop residue and biochar. Leaching experiment was conducted using PVC columns of 45 cm length and the sorption study was conducted using different concentrations of chosen herbicides as per OECD guidelines. Results showed that leaching and movement behavior of the studied herbicides in soil was modified by the applied organic amendments particularly the biochar and maize crop residue. Biochar treated soil retained 29.76, 40.20, and 38.07 percent of the applied pendimethalin, atrazine and imazethapyr respectively in surface 0-15 cm depth and reduced its movement to lower depths and to leachates. Herbicides adsorption was higher with biochar and is indicated by the Koc values of 225, 184 and 22 mg/L for pendimethalin, atrazine and imazethapyr respectively and was followed by the maize crop residue. It is concluded that the application of biochar @ 5t/ha as organic amendment is efficient in decreasing the herbicides movement viz., pendimethalin, atrazine and imazethapyr and modifying their sorption and leaching potential to groundwater.

Assessing the Effect of Intensive Agriculture and Sandy Soil Properties on Groundwater Contamination by Nitrate and Potential Improvement Using Olive Pomace Biomass Slag (OPBS)

The relationship between agricultural activities, soil characteristics, and groundwater quality is critical, particularly in rural areas where groundwater directly supplies local people. In this paper, three agricultural sandy soils were sampled and analyzed for physicochemical parameters such as pH, water content, bulk density, electrical conductivity (EC), organic matter (OM), cation exchange capacity (CEC), and soil grain size distribution. Major and trace elements were analyzed by inductively coupled plasma-optical emission spectrometry (ICP/OES) to determine their concentrations in the fine fraction (FF) of the soils. Afterward, the elemental composition of the soils was identified by X-ray powder diffraction (XRD) and quantified by X-ray fluorescence (XRF). The surface soil characteristics were determined by the Brunauer–Emmett–Teller (BET) method, whereas the thermal decomposition of the soils was carried out using thermogravimetric analysis and differential scanning calorimetric (TGA-DSC) measurements. The morphological characteristics were obtained by scanning electron microscopy (SEM). Afterward, column-leaching experiments were conducted to investigate the soil’s retention capacity of nitrate (NO−3). Parallelly, a chemical and physical study of olive pomace biomass slag (OPBS) residue was carried out in order to explore its potential use as a soil additive and improver in the R’mel area. The OPBS was characterized by physicochemical analysis, assessed for heavy metals toxicity, and characterized using (XRD, XRF, SEM, and BET) techniques. The results show that the R’mel soils were slightly acidic to alkaline in nature. The soils had a sandy texture with low clay and silt percentage (<5% of the total fraction), low OM content, and weak CEC. The column experiments demonstrated that the R’mel irrigated soils have a higher tendency to release large amounts of nitrate due to their texture and a higher degree of mineralization which allows water to drain quickly. The OPBS chemical characterization indicates a higher alkaline pH (12.1), higher water content (7.18%), and higher unburned carbon portion (19.97%). The trace elements were present in low concentrations in OPBS. Macronutrients in OPBS showed composition rich in Ca, K, and Mg which represent 10.59, 8.24, and 1.56%, respectively. Those nutrients were quite low in soil samples. Both XRD and XRF characterization have shown a quasi-dominance of SiO2 in soil samples revealing that quartz was the main crystalline phase dominating the R’mel soils. Oppositely, OPBS showed a reduced SiO2 percentage of 26,29% while K, Ca, and P were present in significant amounts. These results were confirmed by XRF analysis of OPBS reporting the presence of dolomite (CaMg, (CO3)2), fairchildite (K2Ca (CO3)2), and free lime (CaO). Finally, the comparison between the surface characteristic of OPBS and soils by BET and SEM indicated that OPBS has a higher surface area and pore volume compared to soils. In this context, this study suggests a potential utilization of OPBS in order to (1) increase soil fertility by the input of organic carbon and macronutrients in soil; (2) increase the water-holding capacity of soil; (3) increase soil CEC; (4) stabilize trace elements; (5) enhance the soil adsorption capacity and porosity.

Insight on the application of graphene to sandy soils to improve water holding capacity

In this study, the changes in relevant hydraulic parameters (namely hydraulic conductivity, total and effective porosity, specific retention, and longitudinal dispersivity) induced by the introduction of graphene in a calcareous sandy soil and a siliciclastic riverine soil were monitored and modelled via leaching column experiments. Constant pressure head tests were used to calculate the hydraulic conductivity of each column, while leaching experiments were run to estimate total porosity and specific retention, and for each treatment three replicates were done. Columns were then run under saturated conditions via a low flow peristaltic pump and monitored for chloride concentrations. CXTFIT 2.0 was employed to inversely model the column experiments and retrieve effective porosity and longitudinal dispersivity. Results highlighted small changes of hydraulic conductivity and porosity, induced by graphene addition for both soils. A marked increase of specific retention values was instead recorded in the amended columns respect to control ones. Chloride breakthrough curves modelling showed that graphene doubled dispersivity in the calcareous sandy soil compared to the control, while it halved dispersivity in the siliciclastic riverine soil with respect to the control. The results highlight that graphene induces positive shift in the capacity of sandy soil to retain porewater but at the same time it also alters solute transport parameters, like dispersivity, suggesting that further studies need to focus on using several exposure concentrations, durations and mode of exposure, and apply simulated field conditions or perform experiments in real field conditions, to understand the fate of unwanted compound in soils amended with graphene.

Conditional remediation performance of wheat straw biochar on three typical Cd-contaminated soils

Undoubtedly biochar has excellent remediation performance for Cd-contaminated soil. Nevertheless, the remediation performance may be not invariable considering highly variable soil conditions including soil properties and environmental conditions. This work investigated the fate of Cd in three typical Cd-contaminated soils (acidic, neutral and saline-alkali soils) treated with wheat straw biochar and its driving mechanisms under specific soil conditions through aging and remediation experiment, Cd availability experiment and leaching column experiment. The results indicated that biochar addition facilitated Cd immobilization and reduced the uptake of Cd by green vegetables in acidic, neutral and saline-alkali soils under wetting-drying conditions. In contrast to neutral and saline-alkali soils, the release of exchangeable aluminum from biochar-treated acidic soil under flooding-drying cycles lowered the pH of leachate, thus promoting the leaching of Cd from leaching column, especially at 7 and 14 days, when the leaching of Cd increased by 25.3 and 32.6 times, respectively. This result was further supported by the increase in the exchangeable fraction and total leaching amounts of Cd in the topsoil layer (0–20 cm) of biochar-treated acidic soil of leaching column. Additionally, the leaching of Cd was positively correlated with DOC contents of leachate in biochar-treated neutral and saline-alkali soils. In summary, the remediation performance of biochar for Cd-contaminated soils is conditional, and its remediation effect is better in neutral and saline-alkali soils. Notably, the inherent conditions of soil must be fully considered when applying biochar for Cd remediation, especially in acidic Cd-contaminated paddy soils in South China.

Effect of Long Term Fertilization Practices on Tembotrione Movement in Soil: Assessment by Plant Bioassay

The herbicide behavior in soils is executed nowadays via the chemical extraction and instrumental analysis. However, the biological availability and the dynamics of herbicide in soil could be studied effectively through bioassay in the absence of sophisticated techniques and also in situ conditions. Tembotrione is one of the recently registered triketone herbicide and its movement behavior was not studied much in India. Hence the present study was executed to understand the influence of long term fertilization practices on its transport and movement using the bioassay technique involving Randomized Block Design (RBD). The plot wise soil samples were collected from the 50 years old long term fertilization experiment, processed and used to conduct the leaching column (made of PVC) experiment under controlled condition for 30 days. Soil samples were dissected depth wise and residue of tembotrione in each depth was obtained by conducting bioassay using green gram and sunflower as test species. For calibration curve preparation, a separate bioassay was conducted by fortifying tembotrione in control soil at different concentrations. The recorded plant parameters viz., germination percent and biomass after 15th day of both the test species predicted the tembotrione transport efficiently and the results of both the test species were comparable. The tembotrione has shown movement upto 30 cm soil depth and the concentration of residue decreased with increase in soil depth. The long term fertilization practices with the balanced nutrients supply viz., 100% NPK with hand weeding, Zn, FYM showed significant effect on the transport of tembotrione in soil at various depths.
 The study concludes that the plant bioassay technique using green gram and sunflower could be very well used to investigate the transport behavior of Tembotrione in soil. Based on data, tembotrione was identified as moderately mobile compound in sandy clay loam and its movement has been altered by the long term fertilization practices.

Variation of the hydraulic properties in sandy soils induced by the addition of graphene and classical soil improvers

In this study, for the first time, the changes in relevant hydraulic parameters (e.g., hydraulic conductivity, effective porosity, and dispersivity) induced by the introduction of graphene in a calcareous sandy soil and a siliciclastic riverine soil were monitored and modelled via leaching column experiments. Column experiments were also run with traditional soil improvers (compost, biochar, and zeolite) to compare the changes induced by graphene versus well-studied soil improvers. Constant pressure head tests were used to calculate the hydraulic conductivity of each column, while leaching experiments were run to estimate porosity and specific retention, and for each treatment three replicates were done. Columns were then run in saturated conditions via a low flow peristaltic pump and monitored for electrical conductivity, temperature, and chloride. CXTFIT 2.0 was employed to inversely model the column experiments and retrieve parameters like effective porosity, longitudinal dispersivity, bulk thermal diffusivity, and thermal retardation factor. Results highlighted small changes of hydraulic conductivity, porosity, and effective porosity induced by graphene addition (as well as by the other soil improvers) for both soils. A marked increase (nearly 20 %) of specific retention values was instead recorded in the amended columns with respect to control ones. Chloride breakthrough curves modelling showed that graphene doubled dispersivity in the calcareous sandy soil (5.82 ± 1.4 cm) compared to the control (2.6 ± 0.29 cm), while it halved dispersivity in the siliciclastic riverine soil (0.31 ± 0.05 cm) with respect to the control (0.65 ± 0.06 cm). Thermal retardation factors were decreased by graphene by approximately 20 % for both soils. The model fitting via TDS (derived from the electrical conductivity monitoring) produced unreliable dispersivity values in most of the experiments due to the nonconservative nature of this parameter compared to chloride. The results highlight that graphene affected dispersivity but did not significantly alter other physical parameters relevant for solutes transport in sandy soils in comparison to classical improvers, thus future studies should focus on the graphene’s effects on nutrients and agrochemicals leaching in unsaturated flow conditions.

Calcium alginate-biochar composite as a novel amendment for the retention and slow-release of nutrients in karst soil

Soil erosion is a prominent environmental problem in karst areas. To reduce the loss of nutrients in karst soil, two kinds of calcium alginate-biochar composites (CA-MBs) were synthesized. Soil column leaching and pot experiments under different treatments were carried out to investigate the retention and slow-release of CA-MBs on nutrients. The results showed that the retention effects of calcium alginate-rice straw biochar composite (CA-MRB300) and calcium alginate-Eupatorium adenophorum biochar composite (CA-MEB600) on nutrients under fertilization were better than that under non-fertilization. The addition of 0.5 wt% CA-MRB300 and CA-MEB600 reduced the loss of nutrients after fertilization, and 0.5 wt% CA-MRB300 reduced the cumulative leaching amount of PO43-, NH4+, NO3-, and K+ by 48.05%, 28.76%, 36.63%, and 9.08%, respectively. Surface precipitation, ion exchange, and physical adsorption were considered to be the main retention mechanisms of different nutrients based on analyzing the physicochemical properties of CA-MBs and their effects on soil physicochemical properties. The addition of 1.5 wt% CA-MRB300 had the best promotion effect on the root length, stem length, and dry weight of soybean under non-fertilization, indicating that CA-MRB300 could be used as a slow-release fertilizer to promote the growth of soybean. This study develops a novel soil amendment to reduce the loss of nutrients in karst soil.

Characteristics of heavy metal migration in farmland

Compared with water and air pollution, soil pollution is highly concealed, has poor self-purification ability, and poses high risks associated with accumulation. Characteristics of heavy metal migration directly affect the quality of the environment, and comparative studies utilizing column leaching and natural leaching experiments have rarely been performed. In this study, we used farmland soil samples from Xiba Town of the Wutongqiao District to determine the differences in leaching characteristics between column leaching and natural leaching tests. The results indicated that the heavy metals were released in two stages, a rapid release followed by a slow release stage. The cumulative amount released during the second stage exhibited regular fluctuations, while the heavy metal release rate was consistent with the heavy metal adsorption properties of the soil. In addition, the release and accumulation of heavy metals in the soil were influenced by many factors that may interact with each other, which could lead to low correlations between the cumulative heavy metals released during the column leaching and natural leaching tests. Simulating natural heavy metal migration trends using the column leaching test was effective to some extent, but there were significant differences between the accumulation sites and accumulated amounts. This study provides a theoretical basis for improving the remediation of soils contaminated by heavy metals.

Organic–inorganic calcium lignosulfonate compounds for soil acidity amelioration

Soil acidification is a problem widely occurring worldwide, which severely threaten food security and agricultural sustainability. Calcium lignosulfonate (CaLS), a cheap and ecofriendly compound, is used for the first time to amend acid soil by utilizing its unique organic and inorganic functional moieties simultaneously. Both column leaching and incubation experiments were conducted to investigate the comparative effects of CaLS (four rates at 5, 10, 15, 20gkg-1) and compared with conventional amendments, including gypsum (5gkg-1), lignin (5gkg-1), L + G (each at 5gkg-1), and control. The soil pH, exchangeable acidity and base cations, organic carbon, and different Al fractions were determined to unravel the ameliorative performance and mechanism of the treatments. Regardless of application modes and dosages, the results demonstrated that CaLS incorporation significantly increased soil pH, exchangeable Ca2+, cation exchange capacity, and organic carbon and decreased the contents of exchangeable acidity, especially exchangeable Al3+. The ameliorative mechanism was that amendment material led to the displacement of H+ and Al3+ off soil colloids by Ca2+. These released H+ and Al3+ which complexed with lignosulfonate anions into soluble organo-Al were all quickly leached from the soil column. The CaLS addition enhanced the transformation of exchangeable Al3+ and low-to-medium organo-Al complexes into highly stable organically bound fractions and immobilized into the soil. The complexing of CaLS functional groups with Al3+ impeded Al3+ from undergoing hydrolysis to produce more H+. As an environmental-friendly material, CaLS can be a promising amendment for soil acidity and Al toxicity amelioration.