Agents In Soil Research Articles

The synergistic effect of biosynthesized CuONPs and phage (ϕPB2) as a novel approach for controlling Ralstonia solanacearum

BackgroundAs a vital soil-borne pathogenic bacterium, Ralstonia solanacearum can cause wilt disease in multiple Solanaceae plants. Several phages, such as ϕPB2, could infect R. solanacearum acting as a potential biological control agent in soil. In addition, some nanoparticles, especially copper preparation, also showed high toxicity on R. solanacearum with low toxicity on plant. However, whether they can be administered in combination and how effective they are in inhibiting the plant disease caused by R. solanacearum is known very little.ResultsIn this work, the characterization of CuONPs using scanning electron microscope, transmission electron microscope, X-ray photoelectron spectroscopy, Fourier transform infrared spectroscopy, and X-ray diffraction ascertained the presence of CuONPs which were nanometer particle of 83 nm. Then it was found that combined application of CuONPs with phage (ϕPB2) was superior to that of ϕPB2 or CuONPs alone in controlling tobacco bacterial wilt, with the CuONPs (250 mg/mL) and phage (106 PFU/mL) ratio being the best, at 79.1%. The combination of CuONPs and ϕPB2 also showed no obvious toxicity on tobacco growth than control like single application of CuONPs or ϕPB2. Furthermore, the transcriptome changes of R. solanacearum analysis indicated that the combination application and single allocation of CuONPs could inhibit “biofilm formation”, molecular function, biological processes, cellular components, metabolic process, and so on. In addition, the combination application showed higher inhibition of motility and biofilm, and better enhancement of cell membrane permeability, protein leakage, MDA concentration, and enzyme activity of their respiratory chain dehydrogenase than single application of CuONPs or phage (ϕPB2). Transcriptomes analysis also supported that the addition of ϕPB2 enhanced the toxicity of CuONPs by influencing the ABC transporters and quorum sensing, metabolic processes, and cellular biosynthetic processes of R. solanacearum.ConclusionIn total, our work not only proposed a novel way to increase the bactericidal effect of nanomaterials by adding phage, but also discovered the influence, synergistic effects, and mechanisms, which is useful to design novel way to combat phytopathogenic bacteria in the complicated environment.Graphical abstract

Soil crust development on playa surfaces of Lake Urmia and its controlling factors: New insights to combat dust sources

The recession of lake shores, including the ones of Lake Urmia (LU), and later exposure of the lake bed sediments to wind erosion as a consequence of climate change and drought, is a devastating phenomenon worldwide. In the absence of stable surface crusts, these areas can be the source of airborne dust causing health and environmental issues. The present study aims at investigating the crust formation and development on Lake Urmia playa (LUP) surfaces through physicochemical and morphological studies and to determine the major factors affecting crust stability. To achieve the above goals, 50 soil crust samples from playa surfaces of the western LU playa were collected. The soil crust thickness and compressive strength were determined by a digital micro penetrometer. By means of X-ray diffraction (XRD), Fourier transform infrared (FTIR) spectroscopy, thermogravimetric analysis (TGA), and scanning electron microscopy (SEM), the main morphological and chemical factors responsible for the crust development and evolution in LUP were identified. Results showed that crust samples from clay flats (CFs) and clay flats-salt crusts (CF-SC) possessed the most stable crusts with a thickness of 2.2 and 1.9 cm and maximum compressive strength of 6709 and 7399 kPa, respectively, while sand sheets (Sa-sheets) showed weak and locally restricted crust development. Evaluation of correlation coefficients (CC) between soil crust physicochemical properties and crust stability parameters revealed that clay, silt, and organic matter enhance the crust stability and decrease the erodible fraction by increasing the crust thickness, while salt content quantified as Na+ concentration and electrical conductivity increase the firmness of the crusts. Interestingly, total carbonates quantified as calcium carbonate equivalent (CCE) correlated negatively with crust stability although pedogenic calcite is known as cementing agent in soils. XRD together with FTIR spectroscopy revealed that calcite is indeed the predominant mineral form in most soils with the exception of Sa-sheets with the highest share of carbonates, in which aragonite prevailed over calcite. While carbonates of pedogenic origin act as cementing agent, geologic carbonates present as coarse aragonite particles decrease soil stability. Therefore, samples with the highest total carbonate content exhibited the weakest crust, which explains the negative correlation between soil crust and CCE. SEM coupled with Energy Dispersive X-ray (EDX) and elemental mapping revealed that NaCl is the major cementing agent of the soil particles in crusts developed on LU playa surfaces. Its coexistence with phyllosilicates has increased the crust stability and resilience against wind erosion in CF and CF-SC samples while in the Sa-sheet samples, the absence of clay-size minerals (silt and clay) along with the prevalence of geologic carbonates (dolomite and aragonite) and lower NaCl content, limited crust formation and stability. This study emphasizes the importance of the intrinsic soil physicochemical properties together with the secondary (pedogenic) carbonate formation and more importantly the presence of NaCl, as the best determining factors controlling crust formation over LU playa surfaces.

Application of cold-adapted microbial agents in soil contaminate remediation: biodegradation mechanisms, case studies, and safety assessments.

The microbial agent technology has made significant progress in remediating nitro-aromatic compounds (NACs), such as p-nitrophenol, 2,4-dinitrophenol, and 2,4,6-Trinitrotoluene, in farmland soil over the past decade. However, there are still gaps in our understanding of the bioavailability and degradation mechanisms of these compounds in low-temperature environments. In this review, we provide a comprehensive summary of the strategies employed by cold-adapted microorganisms and elucidate the degradation pathways of NACs pollutants. To further analyze their metabolic mechanisms, we propose using mass balance to improve our understanding of biochemical processes and refine the degradation pathways through stoichiometry analysis. Additionally, we suggest employing 13C-metabolic flux analysis to track enzyme activity and intermediate products during bio-degradation processes with the aim of accelerating the remediation of nitro-aromatic compounds, particularly in cold regions. Through a comprehensive analysis of pollutant metabolic activities and a commitment to the 'One Health' approach, with an emphasis on selecting non-pathogenic strains, the environmental management strategies for soil remediation could be positioned to develop and implement safe and effective measure.

Study on the physical and chemical properties of lead passivating agent in soil

With the rapid development of industry, heavy metal pollution has seriously damaged the health of soil, and heavy metals spread through the food chain, posing a threat to human health. The firm existence of heavy metals in soil under earthy conditions is a center trouble faced by soil dense metal pollution solidification and correction technology. However, the existing investigation results are mostly controlled to soil passivation experiments using various materials. Macroscopically, heavy metal passivation materials have been selected, but the intrinsic mechanisms of different compound functional groups in soil passivation have been ignored. With the common heavy metal ion Pb2+ as an example, the stability of the combination of heavy metal ions and common ion groups in soil was analyzed in this study by using quantum chemical calculation as the theoretical guidance. The results show that SO42− and PO43−, as functional groups of passivating agents, are used to control lead pollution and have been verified to have good effects. When the pollution is particularly serious and not easy to passivation and precipitation, Fe3+ can be considered to enhance the passivation effect.

Potential utilization of oil shale as a stabilizing material for compressed Earth block

This research aims to produce a compressed Earth block (CEB) product locally from soil collected from North Jordan. The CEB mixture was further stabilized using oil shale (OS) and ordinary Portland cement (OPC). The CEB specimens were thoroughly characterized by studying their mechanical properties (compressive and flexural strength) and durability characteristics (erosion, absorption, and shrinkage tests). Eight mixtures were carried out for the CEB, one of which was the control mix. The other mixtures were carried out by replacing soil with OS, cement, and sand in different proportions. The results showed that higher compressive strength and flexural strength for CEB were obtained in the mixtures that contained 10% of OS and 10% of cement, resulting in an average compressive strength of 10.6 MPa and flexural strength of 0.25 MPa. The absorption increased when the OS increased in the soil. The consequent erosion test was related to the absorption test, where the higher the absorption, the more negative the results of the erosion test. Moreover, oil shale improved the shrinkage properties of the CEB, as the higher the proportion of oil shale in the CEB, the lower the shrinkage. Finally, using oil shale as a stabilizing agent in soil had a clear role in improving the mechanical properties, hiding the shrinkage cracks, and reducing the volume shrinkage value of the CEB.

Role of lactoyl-glutathione lyase of Salmonella in the colonization of plants under salinity stress

Salmonella, a foodborne human pathogen, can colonize the members of the kingdom Plantae. However, the basis of the persistence of Salmonella in plants is largely unknown. Plants encounter various biotic and abiotic stress agents in soil. We conjectured that methylglyoxal (MG), one of the common metabolites that accumulate in plants during both biotic and abiotic stress, plays a role in regulating the plant-Salmonella interaction. The interaction of Salmonella Typhimurium with plants under salinity stress was investigated. It was observed that wild-type Salmonella Typhimurium can efficiently colonize the root, but mutant bacteria lacking MG detoxifying enzyme, lactoyl-glutathione lyase (Lgl), showed lower colonization in roots exclusively under salinity stress. This colonization defect is due to the poor viability of the mutated bacterial strains under these conditions. This is the first report to prove the role of MG-detoxification genes in the colonization of stressed plants and highlights the possible involvement of metabolic genes in the evolution of the plant-associated life of Salmonella.

Microbial Inoculation can Enhance SRI Performance and Reduce Biotic and Abiotic Stresses in Rice

Microbes play crucial roles in plant survival and fitness by mobilizing soil nutrients, enhancing plant performance by producing phytohormones, and protecting plant from biotic and abiotic stresses. SRI crop management system, extrapolatable to improve production of other crops beyond rice, aims to create the best growing environment above and below ground and to mobilize various services from microbes to increase factor productivity. Inoculating crop plants with effective microbial agents, either in consortia or separately, enhances rice crop performance in various ways. This paper presents results from field experiments and offers some explanation of mechanisms accounting for the higher productivity and performance of SRI rice plants with augmentation of microbial agents in soil.

IDENTIFICATION OF POTENTIAL SOIL DEGRADING MICROBIALS CONTAMINATED WITH INSECTICIDES

The high use of insecticides can cause soil contamination in the rice field environment, so a solution is needed to reduce the contamination and the negative impact on human health. One of the efforts that can be done to overcome this problem was by bioremediation. The bioremediation technique was chosen due to it is eco- friendly, efficient, and cost-effective in its application. However, bioremediation relies on the capacity of living organisms to absorb, accumulate, translocate and detoxify pollutants in a polluted environment. The objective of this study is to explore microbes that can be used as bioremediation agents in soil exposed to various types of insecticide contamination. The results of this study was as many as ±56 species of microbes can be used as bioremediation agents for various types of insecticides so that bioremediation needs to be carried out in order to avoid pesticide residues on soil and agricultural products.

On-site generation of reactive oxidative radicals from dithionite treated oxic soil slurry

ABSTRACT Whereas dithionite has been extensively used as a reducing agent in soil and sediment remediation, here, we demonstrate that it can be used as a potential source of oxidizing radical in oxic soils with potential application in organic pollutant remediation. Benzoic acid was used as a probe compound and the generation of its oxidative product para-hydroxybenzoic acid (p-HBA) was detected to quantify the production of oxidative radicals (ROS). By increasing the dithionite concentration from 2.5–10 Mm, the accumulated P-HBA concentration in 120 min increased from 15.0–27 µM. Whereas, above 10 mM, the p-HBA concentration decreased due to radical scavenging. Increasing soil dosage from 2.5–15 g/100 mL the accumulated p-HBA amount increased from 22.8–33.7 µM. Temperature 25–35 oC and pH 6.2–7.5 were favoured for p-HBA generation. Furthermore, we investigated the roles of different active intermediates in the reaction system and proposed the mechanism behind the ROS genearation. This study suggested that dithionite can be used as an active reagent for advanced oxidation remediation in oxic soil medium.

Effect of Temperature on the Properties of Liquid Product from Hydrothermal Carbonization of Animal Manure and Function as a Heavy Metal Leaching Agent in Soil

Hydrothermal carbonization (HTC) is increasingly considered as a promising method to deal with animal manure. Inevitably, using this method for treatment of animal manure led to large amount of hydrothermal liquid. However, the effect of temperature on the characteristics of liquid product that derived from hydrothermal carbonization of animal manure was still incompletely clear. In this study, three types of animal (chicken, dairy, and swine) manures were selected for hydrothermal carbonization at three different temperatures (200, 250, and 300 °C), and the liquid was collected for further analysis, aiming to investigate the effect of temperature on the liquid properties and its potential function as a soil-leaching agent. Results show that high temperature led to high pH, volatile phenol, organic-N and Cr3+ concentration of liquid, but low chroma, COD, inorganic-N and Cr6+ concentration of liquid. Moreover, the manure types, temperature, and their interaction significantly (P<0.001) influenced the selected liquid properties except for BOD based on the two-way analysis of variance, indicating the liquid properties depended on the manure types and temperature. In addition, the extraction of Cu from contaminated soil using the liquid (hydrothermal carbonization of dairy manure, swine manure, and chicken manure at 200 °C) increased by 125%, 178%, and 424%, respectively, compared to distilled water, indicating that liquid can be applied as a promising soil-leaching agent for heavy metal remediation.

Hydrothermal Synthesis of Carbon Nanotubes-Polyaniline(CNT-PANI)Composites and Preliminary Electrochemical Characterization of CNT-PANI Coatings

Heavy metals have a major contribution to biosphere pollution due to toxicity. The detection and monitoring of the environmental agents in soil, water and air is very important for the general health of humans and animals. It has been recently shown that electrochemical techniques such as differential pulse voltammetry (DPV) and square wave anodic stripping voltammetry (SWASV) using modified electrodes are very attractive methods for detecting heavy metals. The aim of this paper is to demonstrate the potential of hydrothermal process combined with electrochemical techniques to obtain modified electrodes based on functionalized carbon nanotubes (CNTs) and polyaniline (PANI) for metals detection. Commercial multi-walled carbon nanotubes (MWCNT) were functionalized by a mixture of HNO3/H2SO4 and further used for hydrothermal synthesis of CNT-PANI composites with different mass ratios. The resulted powders were analyzed by spectral (Fourier-Transform Infrared Spectroscopy) and thermal (Differential Scanning Calorimetry) methods, and then dispersed in a surfactant/electrolyte solution for preliminary electrochemical experiments (cyclic voltammetry, CV and DPV) to obtain modified electrodes. The influence of the CNT: PANI mass ratio and the synthesis time on the formation of composites with the desired structural and electrochemical properties were studied. It was found that CNT-PANI composite powder having mass ratio 1:4 and synthesis time 3h has the best structural and thermal characteristics and formed a weakly conductive film on the surface of the glassy carbon electrode. Preliminary electrochemical tests revealed the electroactive forms of polyaniline, through the presence of characteristic oxidation peaks but also reduction peaks, corresponding to reversible redox reactions, demonstrating that glassy carbon electrode has been electrochemically modified with CNT-PANI coatings. Further studies will be conducted to test the potential application of glassy carbon electrode modified with CNT-PANI coatings as electrochemical sensor for heavy metals detection.

Direct detection of chemical warfare agent simulants in soil by thermal desorption-low temperature plasma-mass spectrometry

For rapid, accurate and real-time detection of trace chemical warfare agents in soil, direct detection of chemical warfare agent simulants in soil by thermal desorption-low temperature plasma ionization-mass spectrometry was developed. Multi-factor analysis of variance was used to quantitatively analyze the factors affecting the ionization efficiency of low temperature plasma based on the emission spectra of the plasma flame. The experimental parameters including the distance between low temperature plasma outlet and thermal desorption device, the flow rate of discharge gas, the temperature of ion source, the thermal desorption temperature and different solvents were optimized. Dimethyl methylphosphonate (DMMP, G-series nerve agent simulant), tributyl phosphate (TBP, V-series nerve agent simulant) and 2-Chloroethyl ethylsulfide (CEES, H-series blister agent simulant) were desorbed and ionized, forming the typical positive ions of [DMMP + H]+, [DMMP-HOCH3+H]+, [TBP + H]+, [TBP-3(C4H8)+H]+ and [CEES-Cl]+, [CEES- C2H4Cl]+. The ions were analyzed using the multiple reaction monitoring (MRM) of triple quadrupole mass spectrometer. Detection limit of the method was 5 pg for DMMP (m/z 125→93, S/N＞3:1), 5 pg for TBP (m/z 267→99, S/N＞3:1) and 5 ng for CEES (m/z 89→61, S/N＞3:1). Trace level of CWA simulants can be directly detected with simple sample pretreatment, suggesting that the thermal desorption-low temperature plasma-mass spectrometry method is useful for quick and direct detection of chemical warfare agents in soil.

Single and combined effect of chelating, reductive agents, and agro-industrial by-product treatments on As, Pb, and Zn mobility in a mine-affected soil over time.

Application of chelating and reductive agents in soils can increase the availability of potentially toxic elements facilitating their uptake by plants. This study discusses the effect of single or combined EDTA (E), sodium dithionite (SD), and olive mill wastewater (OMW) treatments on As, Pb, and Zn mobility over time in a heavily contaminated mine-affected soil. Soil samples were incubated for 1, 3, 7, 15, 30, 60, and 90days and at each incubation time the easily mobilizable fraction obtained by (NH4)2SO4 (for As) and CH3COOH (for Pb/Zn). The results showed that the highest availability of As (mean value 41mgkg-1) was observed for the EDTA treatment followed by E+OMW (mean value 32mgkg-1) and E+SD+OMW (mean value 27mgkg-1). For Pb and Zn, significantly higher available concentrations were obtained by the EDTA and E+OMW treatments (mean values 2532mgkg-1 and 1427mgkg-1 for Pb and Zn respectively) followed by the E+SD (mean value 2259 and 1333mgkg-1 for Pb and Zn) and E+SD+OMW treatments (mean value 2388 and 1340mgkg-1 for Pb and Zn). Moreover, the incubated for 90days soil samples subjected to two different sequential extraction protocols (SEPs): Wenzel (for As) and BCR (for Pb, Zn, Fe, and Mn). The results showed that As, Pb, and Zn mobility was mainly regulated by the amorphous Fe oxides. Our findings suggest that OMW application in soils should focus more attention since when combined with other amendments produced contradictory results.

Arsenic stabilization performance of a novel starch-modified Fe-Mn binary oxide colloid

Arsenic (As) is an environmentally hazardous contaminant and can be a serious threat to human health. In China, the remediation needs for a large number of As-contaminated sites renders a strong demand for efficient remedial reagents and cost-effective approaches. In this study, a novel starch-modified FeMn binary oxide (SFM), an amorphous colloidal material, has been synthesized as a remedial reagent and its As stabilization performance has been evaluated. A set of laboratory batch experiments were carried out with SFM of different dosages directly added into three contaminated soils to immobilize As. Results demonstrated that SFM could transform As in soil from non-specifically and specifically sorbed fractions to the more stable form bounded to amorphous iron hydrous oxides, thus reducing the As concentration in TCLP leachates by up to 93.2%. Results from adsorption tests and microscopic analysis indicated that the interactions between SFM and As are mainly controlled by adsorption, oxidation, and precipitation processes. SFM has abundant surface hydroxyl groups, with excellent adsorption properties for both As(V) and As(III), with the maximum adsorption capacities of 160.63 and 284.64 mg/g respectively at pH 7.0. The adsorption process closely fitted pseudo second-order kinetics and Freundlich isotherm model. SFM could increase soil Eh and oxidize As(III) to As(V), which facilitated the As stabilization in soil. Colloidal iron-based material directly used for stabilization in As contaminated soils is reported here for the first time. Starch modification improves both the reactivity and mobility of the stabilization agent in soil. Our findings propose an efficient and convenient reagent for As remediation in soil.

Copper sulfate-resistant bacteria isolated from Blue Soil Hills, Sagada, Mountain Province, Philippines

The objective of this study was to isolate copper sulfate-resistant bacteria in Blue Soil Hills, Sagada, Mountain, Province, Philippines. Three distinct bacterial colonies were isolated from the soil sample. The isolates were different from one another based upon colonial characteristics and growth patterns in solid and liquid medium. All three bacteria were gram-positive and were able to grow in medium supplemented with various concentrations of copper sulfate. More luxurious growth was observed in medium with highest supplementation (333.33 ppm). The isolated bacteria could be potential bioremediation agents in soil and water heavily contaminated with copper. Keywords: Copper sulfate, bioremediation, Blue Soil Hills, Sagada, Mountain Province

Formation and Morphology Evolution from Ferrihydrite to Hematite in the Presence of Tartaric Acid

Hematite, with ferrihydrite as the common precursor, is the most stable iron oxide in soils and sediments and has many applications in environmental systems. As a common reducing agent in soils, tartaric acid (L-TA) can reduce Fe3+ to Fe2+ and template the formation of hematite from ferrihydrite. Here, the formation of hematite in the presence of L-TA was investigated under different L-TA concentrations, initial suspension pH, and aging time. The products were characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM), and high- resolution transmission electron microscopy (HRTEM). Both the transformation process and the particle morphology of hematite were affected by the initial suspension pHi at which the L-TA was added to the suspension. Optimal pHi values at a L-TA/Fe(III) molar ratio of 1.0% and an aging time of 10 h at 100 °C were pHi 7 and pHi 11. At pHi 7, the optimal L-TA/Fe(III) molar ratio for the transformation was 1.0% and aging at 100 °C was completed after about 20 h. The ...

Supplementing biocontrol agents with botanicals improved growth and yield of coriander (Coriandrum sativum L.) infected with Protomyces macrosporus Unger

This investigation was carried out to examine the effect of some biocontrol agents (Trichoderma viride, T. harzianum, Azotobacter chroococcum, Pseudomonas putida) and botanicals (Melia azedarach, Eucalyptus globulus, Calotropis procera) both alone and in combination on growth, yield and stem gall disease of coriander (Coriandrum sativum L.) caused by Protomyces macrosporus Unger in a pot experiment. Plants inoculated with P. macrosporus caused significant reduction in growth and yield attributes as compared to untreated control. Stem gall intensity was recorded 59% in plants treated with pathogen alone. The results revealed that, application of biocontrol agents / botanicals both alone and in combination caused significant reduction in stem gall intensity (20.33–84.82%) as compared to control. Among the tested biocontrol agents, T. viride was found superior in enhancing the growth and yield as well as reduction in stem gall intensity (44.37%). Application of biocontrol agents in soil supplemented with botanicals was found more beneficial in enhancing plant growth and yield attributes as well as reducing stem gall intensity (52.54–84.82%). Among various combinations tested T. viride + Melia azedarach and T. viride + E. globulus caused greater increase in plant growth and yield characters both in pathogen inoculated as well as uninoculated plants.

Influence of Bacillus subtilis B068150 on cucumber rhizosphere microbial composition as a plant protective agent

Our aim was to investigate factors that influenced bacterial and fungal community composition in the cucumber rhizosphere with the addition of Bacillus subtilis B068150 in soils. Using pyrosequencing, we tracked changes in total bacterial and fungal community composition and structures in cucumber rhizosphere planted in clay, loam and sandy soils and inoculated with B. subtilis B068150. B. subtilis B068150 colonized the rhizosphere of cucumber without altering the indigenous microbial community composition. B068150 strain did not significantly affect microbial diversity in cucumber rhizosphere, but both soils texture and chemistry did, based on principal coordinates analysis (PCoA), hierarchical clustering in UniFrac, and canonical correspondence analysis (CCA). Shannon diversity values (H′) suggest that rhizosphere diversity varied among the three soils with the significant highest diversity observed in loamy soil. Fungi were dominated by Ascomycota, Chytridiomycota, Basidiomycotina, with Ascomycota accounting for 29.1%. Fusarium was found only in cucumber rhizosphere grown in loamy soil; however, this did not affect the health of cucumber in three loamy soils during the three months study. Bacillus subtilis B068150 could be an environmental compatible plant protective agent in soils depending on the soil type.

Differential Sorption Behavior of Cadmium, Lead, Zinc, and Copper in Some Tropical Soils and Their Environmental Implications

ABSTRACTThis study evaluated cadmium (Cd), lead (Pb), zinc (Zn), and copper (Cu) sorption characteristics of three tropical soils. Data obtained conformed to Freundlich sorption model and the S-shaped isotherm curve. Sorption efficiency of Zn and Pb were highest in alkaline soil while slightly acid soil had the highest Cd and Cu sorption efficiency for monometal sorption. In competitive sorption, metals were more sorbed in slightly acid soil while the least efficiency was recorded in acid soil. Distribution coefficient; Kd (average across soil types) in monometal sorption followed the order: Pb > Zn > Cd > Cu. For competitive sorption, the order was Zn > Pb > Cu > Cd. When in competition, Cd was preferentially sorbed in slightly acid and alkaline soils and Zn for acid soil. Conclusively, lead is more in equilibrium solution when in competition with Cd, Zn and Cu making it potential agent of soil and groundwater pollution.

Effect of oxidizing and reducing agents in soil on methane production in Southeast Asian paddies

ABSTRACTMethane is one of the greenhouse gases emitted from paddy soil ecosystems and may induce global warming and climate change; therefore, mitigation options are urgently required to establish mitigation technology to reduce methane emission without affecting rice production. Methane is produced by a balance between oxidizing agents (such as iron) and reducing agents (easily decomposable soil organic matter), according to the so-called Takai theory. To evaluate options for mitigating methane production potential and to examine the applicability of the Takai theory in Southeast Asian paddy soils, 23 soil samples were collected from Thailand, Indonesia, Philippines, and Vietnam. These soil samples were anaerobically incubated to measure their methane production potential and examined to see whether their chemical properties, such as the ferrous, total iron, and organic matter contents, were correlated. We found a significant negative correlation between the methane production potential and the total iron content, and a positive correlation between the methane production potential and the hexose content, as an index for a soil’s easily decomposable organic matter content. The methane–C/CO2–C production ratio was also positively correlated with the mineralizable nitrogen/ferrous contents ratio, which indicated that the Takai theory, established for Japanese paddy soils, is also useful in Southeast Asian paddy soils and that the soil’s iron content is important to estimate the methane production potential.