Soil In Thailand Research Articles

Antibiotic Susceptibility of Bacteria Isolated from Livestock-exposed and Unexposed Areas in Perlite-rich Soil in Thailand

Antibiotic resistant bacteria are present in various environments and are concerning for public health. Antibiotic resistance genes in soil may proliferate throughout different ecosystems and be acquired by pathogens that pose health risks to humans and animals. This study investigated the antibiotic resistance of cultivable bacteria isolated from livestock-exposed and unexposed areas in a former perlite mining area in the Fa-La-Mee Mountain range, Lopburi, Thailand. Soil samples were collected in five different locations. Soil bacteria were isolated and tested for susceptibility against seven antibiotics, followed by 16S rRNA gene-based identification. A total of 56 bacterial isolates were isolated from the perlite-rich soil samples, including 34 isolates from the livestock-exposed areas and 22 isolates from the unexposed areas. Most of the isolates were resistant to cefepime (26.5% in exposed areas and 22.7% in unexposed areas) and ampicillin (23.5% in exposed areas and 22.7% in unexposed areas). 16S rRNA gene sequences revealed that most of the resistant bacteria isolated from perlite-rich soil were Bacillus spp. A multidrug-resistant isolate of Bacillus cereus resistant to ampicillin, trimethoprim/sulfamethoxazole, and cefepime was found in a livestock-unexposed area. The majority of the culturable antibiotic-resistant bacteria isolated from perlite-rich soil were cefepime-resistant Bacillus. Interestingly, the pattern of antibiotic resistance in exposed and unexposed areas was not different, which indicated that antibiotic resistance in perlite-rich soil is likely caused by other factors, such as physicochemical characteristics and/or the microbial population of the soil rather than by antibiotics used in livestock husbandry.

Iron Oxyhydroxide Transformation in a Flooded Rice Paddy Field and the Effect of Adsorbed Phosphate.

The mobility and bioavailability of phosphate in paddy soils are closely coupled to redox-driven Fe-mineral dynamics. However, the role of phosphate during Fe-mineral dissolution and transformations in soils remains unclear. Here, we investigated the transformations of ferrihydrite and lepidocrocite and the effects of phosphate pre-adsorbed to ferrihydrite during a 16-week field incubation in a flooded sandy rice paddy soil in Thailand. For the deployment of the synthetic Fe-minerals in the soil, the minerals were contained in mesh bags either in pure form or after mixing with soil material. In the latter case, the Fe-minerals were labeled with 57Fe to allow the tracing of minerals in the soil matrix with 57Fe Mössbauer spectroscopy. Porewater geochemical conditions were monitored, and changes in the Fe-mineral composition were analyzed using 57Fe Mössbauer spectroscopy and/or X-ray diffraction analysis. Reductive dissolution of ferrihydrite and lepidocrocite played a minor role in the pure mineral mesh bags, while in the 57Fe-mineral-soil mixes more than half of the minerals was dissolved. The pure ferrihydrite was transformed largely to goethite (82-85%), while ferrihydrite mixed with soil only resulted in 32% of all remaining 57Fe present as goethite after 16 weeks. In contrast, lepidocrocite was only transformed to 12% goethite when not mixed with soil, but 31% of all remaining 57Fe was found in goethite when it was mixed with soil. Adsorbed phosphate strongly hindered ferrihydrite transformation to other minerals, regardless of whether it was mixed with soil. Our results clearly demonstrate the influence of the complex soil matrix on Fe-mineral transformations in soils under field conditions and how phosphate can impact Fe oxyhydroxide dynamics under Fe reducing soil conditions.

Raw starch degrading alkaline α-amylase from Geobacillus kaustophilus TSCCA02: Production, characterization, and its potential for application as a detergent additive.

Geobacillus kaustophilus TSCCA02, a newly isolated strain from cassava (Manihot esculenta L.) rhizosphere soil in Thailand, showed maximum raw starch degrading enzyme (RSDE) activity at 252.3 ± 9.32 U/mL with cassava starch and peptone at 5.0 and 3.0 g/L, respectively. 16 S ribosomal RNA (rRNA) sequencing and phylogenetic tree analyses indicated that the TSCCA02 strain was closely related to G. kaustophilus. The crude RSDE had optimal activity at 60°C and pH 9.0. This enzyme degraded various kinds of starch including potato starch, cassava starch, rice flour, corn starch, glutinous rice flour, and wheat flour to produce sugar syrup at 60°C, as confirmed by scanning electron microscopy (SEM), thin-layer chromatography (TLC), and Fourier-transform infrared spectroscopy (FTIR). The major end products of starch hydrolysis were maltose and maltotriose with a small amount of glucose, confirming this enzyme as an α-amylase. The enzyme improved the washing efficiency of cotton fabric with commercial detergent. Results indicated the potential of alkaline α-amylase produced from a new isolate of G. kaustophilus TSCCA02 for application as a detergent additive on an industrial scale.

Streptomyces monashensis MSK03-mediated synthesis of gold nanoparticles: characterization and antibacterial activity.

Nanotechnology is a cutting-edge field with diverse applications, particularly in the utilization of gold nanoparticles (AuNPs) due to their stability and biocompatibility. AuNPs serve as pivotal components in medical applications, with a specific emphasis on their significant antibacterial efficacy. This study focuses on synthesizing AuNPs using the cell-free supernatant of Streptomyces monashensis MSK03, isolated from terrestrial soil in Thailand. The biosynthesis process involved utilizing the cell-free supernatant of S. monashensis MSK03 and hydrogen tetrachloroauric acid (HAuCl4) under controlled conditions of 37 °C and 200 rpm agitation. Characterization studies revealed spherical AuNPs with sizes ranging from 7.1 to 40.0 nm (average size: 23.2 ± 10.7 nm), as confirmed by TEM. UV-Vis spectroscopy indicated a localized surface plasmon resonance (LSPR) band at 545 nm, while XRD analysis confirmed a crystalline structure with characteristics of cubic lattice surfaces. The capping molecules on the surface of AuNPs carry a negative charge, indicated by a Zeta potential of -26.35 mV, and FTIR analysis identified functional groups involved in reduction and stabilization. XANES spectra further confirmed the successful reduction of Au3+ to Au0. Moreover, the synthesized AuNPs demonstrated antibacterial activity against drug-resistant strains of Pseudomonas aeruginosa and Acinetobacter baumannii. Interestingly, the AuNPs showed non-toxicity to Vero cell lines. These significant antibacterial properties of the produced nanoparticles mean they hold great promise as new antimicrobial treatments for tackling the increasing issue of antibiotic resistance.

Confidence Interval for the Population Mean of Rayleigh Distribution with Application to Shear wave Velocity of Soils in Thailand

Confidence Interval for the Population Mean of Rayleigh Distribution with Application to Shear wave Velocity of Soils in Thailand

Isolation and characterization of novel Dothideomycetes species from forest soils in Chiang Rai and Krabi (Thailand): additions to the diversity of Curvularia and Verruconis

Fungi are adapted to diverse environments, where the forest soils have complex fungal communities with a wide range of lifestyles. This study aims to explore and isolate Dothideomycetes from the forest soils in Thailand. Sampling sites were located in Chiang Rai and Krabi provinces. Cultures were obtained through soil dilution series, and the strains were subjected to morphological observations and multigene phylogenetic analyses for identification. Maximum likelihood and Bayesian inference analyses were conducted to clarify their phylogenetic affinities using partial nuclear ribosomal DNA (ITS, LSU, and SSU) and the protein-coding genes (tef1-α and GADPH). Herein, two new species (Curvularia chiangraiensis sp. nov. and Verruconis soli sp. nov.) and two new records (C. chiangmaiensis and V. thailandica) are described based on the morphological and phylogenetic evidence. Curvularia chiangraiensis sp. nov. is distinguished by its relatively smaller conidia and the presence of sympodial proliferation of conidiogenesis and Verruconis soli sp. nov. exhibits micronematous conidiophores and obovoid conidia that transform into sub-cylindrical or ellipsoidal shapes, and becoming 1-septate when mature. These unique characteristics set them apart from closely related taxa. The newly described taxa have been subjected to a thorough comparison with closely related species, enabling a comprehensive analysis. The study offers detailed descriptions and includes high-quality micrographs, with the aim of providing a comprehensive understanding of these newly identified taxa

Occurrence of Heat-Resistant Mold Ascospores in Pineapple and Sugarcane Field Soils in Thailand.

Heat-resistant molds (HRMs) are important spoilage fungi of heat-processed fruit products worldwide. Ascospores of HRMs are widely distributed in the soil in which fruits are grown and are often found associated with raw fruit materials. To date, there is little available information on the distribution of HRMs in the soil and on their heat resistance. Thus, this study determined the presence and characterized the heat resistance of HRMs in soil samples from pineapple and sugarcane fields in Thailand. HRMs were detected in all soil samples, and the most dominant species was Aspergillus with 50-99.2% relative abundance. Other isolates, in descending order of frequency, were Penicillium, Talaromyces, Hamigera, and Paecilomyces. Then, 100 representative HRM isolates were identified based on a combination of morphological characteristics and ITS sequences. They were classified into 5 genera and 24 species. The heat resistance of ascospores aged 30 days produced by selected HRMs was qualitatively determined in a glucose-buffered solution. Based on their log reductions after heat shock at 75°C for 30 min, they were classified as less, moderately, or highly heat-resistant ascospores. HRMs belonging to A. chevalieri, A. denticulatus, A. siamensis, A. laciniosus, A. fennelliae, A. spinosus, Paec. niveus, H. pallida, and T. macrosporus produced high heat-resistant ascospores. In addition, soil physicochemical properties significantly influenced the prevalence of HRMs, depending on the fungal genus. The thermal resistance of ascospores was significantly and positively correlated to available phosphorus, whereas it was negatively correlated to soil pH. The results of this study confirmed the presence of HRMs in soils and potential HRM contamination, especially in fruits growing in acidic or high-nutrient soils, or both.

Occurrence of entomopathogenic nematodes, Oscheius myriophilus Poinar in Thailand: Preliminary characterization of novel isolates and biological control potential against insect pests

AbstractNumerous nematodes in the genus Oscheius possess entomopathogenic abilities. These nematodes also kill their insect hosts by releasing their symbiotic bacteria within 48–72 h. In this study, 12 indigenous isolates of Oscheius myriophilus based on molecular, morphological, and morphometric studies were recovered from different undisturbed soils in Thailand. Moreover, the virulence of 12 O. myriophilus at a rate of 25 IJs/cm2 against fifth‐instar larvae of Galleria mellonella ranged from 56%–86% after 72 h of exposure. Oscheius myriophilus EPNKU40 exhibited the highest efficacy in causing mortality in the insect larvae. It also killed third‐instar larvae of Spodoptera litura and Spodoptera exigua up to 60% after 72 h of exposure. The median lethal concentration (LC50) values of O. myriophilus EPNKU40 against G. mellonella larvae after 48 and 72 h of exposure were 11 and 4 IJs/cm2, respectively. The discovery of O. myriophulus is the first record in Thailand characterized using morphological, morphometric, and molecular diagnostic tools, which have shown lethal effects against insect pests and can later be utilized as biocontrol agents after several comprehensive assessments.

Measurement of Dielectric Properties in Soil Contaminated by Biodiesel-Diesel Blends Based on Radio Frequency Heating

Several recent studies have found that measuring the dielectric permittivity of soil can be used to determine the level of environmental pollution. However, there is limited research on the measurement of dielectric properties in soil contaminated with biodiesel-diesel blends from Thailand. This paper presents to monitor the dielectric properties of soil contaminated with biodiesel-diesel blends. Specifically, we use the commercial grade diesel B7 to contaminate a sample of sand soil. We also study the measurement of dielectric properties in contaminated soil with the diesel B7 using a dual electrode plate-based radio frequency (RF) heating system. This allows us to observe the behavior of the contaminated soil before and after RF heating treatment. The experimental result showed that the dielectric properties of uncontaminated and contaminated soil were different. In addition, the RF heating system utilizing the electric field intensities of 450 kV/m resulted in the dielectric properties of the contaminated soil becoming similar to those of uncontaminated soil. These findings suggest that using RF heating on contaminated soil samples improve the air in the pore space compared to unheated contaminated soil. This approach may be effective for the treatment of soil in Thailand using an RF heating system with dual electrode plates.

Streptomyces humicola sp. nov., a novel actinobacterium isolated from peat swamp forest soil in Thailand.

A polyphasic approach was used to describe strain RB6PN25T, an actinobacterium isolated from peat swamp forest soil in Rayong Province, Thailand. The strain was a Gram-stain-positive and filamentous bacterium that contained ll-diaminopimelic acid, mannose and ribose in whole-cell hydrolysates. MK-9(H8) was the major menaquinone. The major fatty acids were iso-C16 : 0, anteiso-C15 : 0 and iso-C15 : 0. The polar lipid profile consisted of diphosphatidylglycerol, phosphatidylethanolamine, phosphatidylinositol, two unidentified glycophospholipids, two unidentified aminolipids and an unidentified phospholipid. The 16S rRNA gene sequences analysis indicated that it was most closely related to Streptomyces rubrisoli DSM 42083T (97.6 %) and Streptomyces palmae TBRC 1999T (97.4 %). Strain RB6PN25T exhibited low average nucleotide identity and digital DNA-DNA hybridization values with S. rubrisoli DSM 42083T (78.6 %, 23.2 %) and S. palmae TBRC 1999T (76.0 %, 22.6 %). The DNA G+C content of strain RB6PN25T was 69.9%. The results of phenotypic, chemotaxonomic, genotypic and phylogenetic analyses reveal that strain RB6PN25T represents a novel species of the genus Streptomyces, for which the name Streptomyces humicola sp. nov. is proposed. The type strain is RB6PN25T (=TBRC 14819T=NBRC 115204T).

Diversity and activity of amylase-producing bacteria isolated from mangrove soil in Thailand

Abstract. Klinfoong R, Thummakasorn C, Ungwiwatkul S, Boontanom P, Chantarasiri A. 2022. Diversity and activity of amylase-producing bacteria isolated from mangrove soil in Thailand. Biodiversitas 23: 5519-5531. Mangrove forests are a potential ecosystem for the isolation of various economic enzymes derived from mangrove-associated bacteria. The knowledge of amylase-producing bacteria isolated from mangrove forests in the Southeast Asian region has been scarce. This study aimed to investigate the isolation, genetic identification, and activity characterization of amylase-producing bacteria from mangrove soils in Thailand. The amylase-producing bacteria isolated from mangrove soils in the present were genetically belong to the genera Bacillus, Desulfurella, Peribacillus, Priestia, and Pseudomonas. Several amylase-producing bacteria such as Bacillus proteolyticus, Desulfurella, Pseudomonas entomophila, and Pseudomonas putida found in this study have hardly ever been reported. The Bacillus paralicheniformis strain DNP0507 was the most active amylolytic bacterium with 2.395 ± 0.133 U/mg of amylase activity. The optimum temperature and pH for amylolytic activity were determined to be 50°C at a pH of 7.0 with a thermal stability range of 20-60°C at a neutral pH of 7.0-8.0. The enzyme activity was significantly enhanced by Cu2+, Co2+, and Pb2+ and was inhibited considerably by a chelating agent EDTA. Finally, the most active amylolytic B. paralicheniformis strain DNP0507 could be applied in baking industries, food industries, and starchy waste valorization.

Discovery of Oleaginous Yeast from Mountain Forest Soil in Thailand.

As an interesting alternative microbial platform for the sustainable synthesis of oleochemical building blocks and biofuels, oleaginous yeasts are increasing in both quantity and diversity. In this study, oleaginous yeast species from northern Thailand were discovered to add to the topology. A total of 127 yeast strains were isolated from 22 forest soil samples collected from mountainous areas. They were identified by an analysis of the D1/D2 domain of the large subunit rRNA (LSU rRNA) gene sequences to be 13 species. The most frequently isolated species were Lipomyces tetrasporus and Lipomyces starkeyi. Based on the cellular lipid content determination, 78 strains of ten yeast species, and two potential new yeast that which accumulated over 20% of dry biomass, were found to be oleaginous yeast strains. Among the oleaginous species detected, Papiliotrema terrestris and Papiliotrema flavescens have never been reported as oleaginous yeast before. In addition, none of the species in the genera Piskurozyma and Hannaella were found to be oleaginous yeast. L. tetrasporus SWU-NGP 2-5 accumulated the highest lipid content of 74.26% dry biomass, whereas Lipomyces mesembrius SWU-NGP 14-6 revealed the highest lipid quantity at 5.20 ± 0.03 g L−1. The fatty acid profiles of the selected oleaginous yeasts varied depending on the strain and suitability for biodiesel production.

Biosynthesis of P(3HB-co-3HHx) Copolymers by a Newly Engineered Strain of Cupriavidus necator PHB−4/pBBR_CnPro-phaCRp for Skin Tissue Engineering Application

Polyhydroxyalkanoates (PHAs) are biodegradable polymers synthesized by certain bacteria and archaea with functions comparable to conventional plastics. Previously, our research group reported a newly PHA-producing bacterial strain, Rhodococcus pyridinivorans BSRT1-1, from the soil in Thailand. However, this strain’s PHA synthase (phaCRp) gene has not yet been characterized. Thus, this study aims to synthesize PHA using a newly engineered bacterial strain, Cupriavidus necator PHB−4/pBBR_CnPro-phaCRp, which harbors the phaCRp from strain BSRT1-1, and characterize the properties of PHA for skin tissue engineering application. To the best of our knowledge, this is the first study on the characterization of the PhaC from R. pyridinivorans species. The results demonstrated that the expression of the phaCRp in C. necator PHB−4 had developed in PHA production up to 3.1 ± 0.3 g/L when using 10 g/L of crude palm kernel oil (CPKO) as a sole carbon source. Interestingly, the engineered strain produced a 3-hydroxybutyrate (3HB) with 2 mol% of 3-hydroxyhexanoate (3HHx) monomer without adding precursor substrates. In addition, the 70 L stirrer bioreactor improved P(3HB-co-2 mol% 3HHx) yield 1.4-fold over the flask scale without altering monomer composition. Furthermore, the characterization of copolymer properties showed that this copolymer is promising for skin tissue engineering applications.

Using Soil P Tests and P-Sorption Index to Predict P Requirement for Cassava Grown in Tropical Upland Sandy Soils

ABSTRACT The phosphorus (P) sorption index and efficiency of P extracting methods were investigated to quantify the available P content for accurate recommendations regarding cassava P fertilizer application in the sandy soils of Thailand. Phosphorus sorption isotherms were examined to predict the response of soils to the P fertilizers applied. Six rates of P fertilizers (0, 12.5, 25, 37.5, 50 and 62.5 kg P2O5 ha−1) were applied in a randomized complete block design at five field sites in major cassava-growing areas. The efficiency among the Bray II, CaCl2 and Mehlich III extracts was also tested by comparing their capacity to predict crop response. The P adsorption capacities of all soils were in the range 39.4–106 mg kg−1; therefore, there were classified as low P-sorbed soils. Phosphorus fertilizer produced significantly higher aboveground biomass than did zero-P fertilization. The critical P level adequate for 95% of the maximum yield was in the range 0.14–0.26 mg P L−1. The equation for calculating P fertilizer using soil P extracted based on the Bray II, CaCl2 and Mehlich III methods had accuracy levels of 73, 65 and 72%, respectively. Bray II was slightly superior to Mehlich III for use in soil-P availability indices, both of which were recommended for P fertilizer assessment.

Pseudonocardia terrae sp. nov., an actinobacterium isolated from rice rhizosphere soil in Thailand.

A novel actinomycete, designated strain RS11V-5T, was isolated from rhizosphere soil of Oryza sativa L. collected from Roi Et Province, Thailand, and its taxonomic position was evaluated. Cells of strain RS11V-5T were Gram-stain-positive, aerobic, and non-motile. Whole-cell hydrolysates contained meso-diaminopimelic acid, arabinose, galactose, glucose and ribose. MK-8(H4) was detected as the predominant menaquinone of this strain. The polar lipids were diphosphatidylglycerol, phosphatidylmethylethanolamine, phosphatidylethanolamine, hydroxy-phosphatidylmethylethanolamine, hydroxy-phosphatidylethanolamine, an unidentified phospholipid, an unidentified aminolipid and an unidentified glycolipid. The major fatty acids were iso-C16 : 0, C16 : 0 and C16 : 1 ω7c/C16 : 1 ω6c. Phylogenetic analyses based on the 16S rRNA gene sequences showed that strain RS11V-5T belonged to the genus Pseudonocardia and had high 16S rRNA sequence similarity of 99.3 % to Pseudonocardia kujensis KCTC 29062T and less than 98.4 % to other members of the genus Pseudonocardia. The DNA G+C content of the strain RS11V-5T was 73.3 mol%. Strain RS11V-5T showed 46.5 % digital DNA-DNA hybridization, 92.2 % orthologous average nucleotide identity (OrthoANI), 90.2 % ANI based on blast and 92.7 % ANI based on MUMmer to P. kujensis KCTC 29062T. Based its phenotypic, genotypic, phylogenetic and chemotaxonomic characteristics, strain RS11V-5T represents a novel species of the genus Pseudonocardia, for which the name Pseudonocardia terrae sp. nov. is proposed. The type strain is RS11V-5T (=TBRC 15286T=NBRC 115296T).

Amazonocrinis thailandica sp. nov. (Nostocales, Cyanobacteria), a novel species of the previously monotypic Amazonocrinis genus from Thailand

Cyanobacteria are distributed worldwide, and many new cyanobacterial species are discovered in tropical region. TheNostoc-like genus Amazonocrinis has been separated from the genus Nostoc based on polyphasic methods. However,species diversity within this genus remains poorly understood systematically because only one species (Amazonocrinisnigriterrae) has been described. In this study, two novel strains (NUACC02 and NUACC03) were isolated from moist ricefield soil in Thailand. These two strains were characterized using a polyphasic approach, based on morphology, 16S rRNAphylogenetic analysis, internal transcribed spacer secondary structure and ecology. Phylogenetic analyses based on 16SrRNA gene sequences confirmed that the two novel strains formed a monophyletic clade related to the genus Amazonocrinisand were distant from the type species A. nigriterrae. The 16S rRNA gene sequence similarity (<98.1%) betweennovel strains and all other closely related taxa including the Amazonocrinis members exceeded the cutoff for speciesdelimitation in bacteriology, reinforcing the presence of a new Amazonocrinis species. Furthermore, the novel strainspossessed unique phenotypic characteristics such as the presence of the sheath, necridia-like cells, larger cell dimensionand akinete cell arrangement in long-chains and the singularity of D1–D1′, Box-B, V2, and V3 secondary structures thatdistinguished them from other Amazonocrinis members. Considering all the results, we described our two strains as Amazonocrinisthailandica sp. nov. in accordance with the International Code of Nomenclature for Algae, Fungi and Plants.

Assessing DNA extraction methods for metagenomic analysis from crop soil in Thailand

Assessing DNA extraction methods for metagenomic analysis from crop soil in Thailand

Taxonomic and Metabolite Diversities of Moss-Associated Actinobacteria from Thailand

Actinobacteria are a group of ecologically important bacteria capable of producing diverse bioactive compounds. However, much remains unknown about the taxonomic and metabolic diversities of actinobacteria from many geographic regions and ecological niches. In this study, we report the isolation of actinobacteria from moss and moss-associated rhizosphere soils in Thailand. Among the 89 isolates analyzed for their bioactivities, 86 strains produced indole-3-acetic acid (IAA, ranging from 0.04 to 59.12 mg/L); 42 strains produced hydroxamate type of siderophore; 35 strains produced catecholate type of siderophore; 21 strains solubilized tricalcium phosphate; and many strains exhibited antagonistic activities against one to several of the seven selected plant, animal, and human pathogens. Overall, actinobacteria from the rhizosphere soil of mosses showed greater abilities to produce IAA and siderophores and to solubilize tricalcium phosphate than those from mosses. Among these 89 isolates, 37 were analyzed for their 16S rRNA gene sequences, which revealed their diverse phylogenetic distributions among seven genera, Streptomyces, Micromonospora, Nocardia, Actinoplanes, Saccharothrix, Streptosporangium, and Cryptosporangium. Furthermore, gas chromatography-mass spectrometry analyses of ethyl acetate crude extracts of three selected isolates with inhibitory effects against a methicillin-resistant Staphylococcus aureus strain revealed diverse metabolites with known antimicrobial activities. Together, our results demonstrate that actinobacteria from mosses in Thailand are taxonomically diverse and capable of producing a range of metabolites with plant-growth-promoting and microbial pathogen-inhibiting potentials.

Litter Quality and Microbes Explain Aggregation Differences in a Tropical Sandy Soil

Soil aggregates store most soil organic carbon (SOC), but how does litter quality influence their formation? We hypothesized varying litter quality to facilitate differences in aggregate formation by altering the seasonal development of microbial biomass (MB) C and N, with MB driving aggregate development in a tropical sandy soil in Thailand. Aggregate development was studied in a long-term fallow experiment, receiving 10 Mg ha−1 annual applications of rice (Oryza sativa) straw (low N and polyphenols (PP)), groundnut (Arachis hypogaea) stover (high N, low PP), tamarind (Tamarindus indica) litter (medium N and PP), or dipterocarp (Dipterocarpus tuberculatus) leaf litter (low N, high PP) compared to a control. N-rich litter from groundnut and tamarind led to significantly higher MB, bulk soil C and aggregate C than dipterocarp, rice straw, and the control. Bulk soil C and small macroaggregates C of N-rich litter treatments increased about 7% in 30 weeks. Increasing MB N explained increasing small macroaggregate C and both, MB C or N were important covariates explaining temporal variations of C stored in themicroaggregates, in silt and clay. MB also explained temporal variations of aggregate fraction weights. With time, SMA C only increased in the N-rich groundnut and tamarind treatments, but decreased in other treatments. Connections of MB to aggregate C and weight substantiated the importance of microbial activity for aggregate formation and carbon sequestration. By promoting MB for longest time spans, medium-quality tamarind could best facilitateaggregate formation, and increase silt and clay C.

Investigation of Metal and Trace Elements of Cenospheres from Lignite High-Calcium Fly Ash (Thailand)

High-calcium fly ashes contain a large content of small particles including cenospheres of chemical constituents known to be similar to fly ash and the parent coal. Coal fly ash contains metal and trace elements that may leach out during disposal or utilization. This work aimed to understand an overview of cenosphere characteristics relating to fly ash and leaching study. To our knowledge, this is the first report on metal and trace element leaching of cenospheres separated from high-calcium (28.9 wt.%) class C fly ash produced from the Mae Moh coal-fired thermal power plant in Thailand. In this study, the cenospheres were separated from fly ash by a wet separation process (sink-float method) using water as medium. Physical properties, morphology, chemical composition, the mineral phases of cenospheres and fly ash have been characterized. Extraction was carried out by acid digestion; the selected metal and trace elements in this study are Mg, Al, Zn, Pb, Cd, Cr, and Cu; the obtained environmentally available concentrations of cenospheres were analyzed in comparison to those of fly ash. The concentrations of Cu, Cr, Pb, and Cd elements of interest in the leachates obtained from the toxicity characteristic leaching procedure (TCLP) showed the tendency to decrease in that order. All the elements were found below the permissible limit values regarding Thailand soil quality standards. Association of the heavy metal trace elements in cenospheres and fly ash was discussed in in terms of physico-chemical-geochemistry correlating with the leaching concentrations.