Fulvic Acid Ratio Research Articles

Enhancing organic matter dissolution and microbial community structure in waste activated sludge using thermal-alkali-rhamnolipid pretreatment: Focus on thermal optimization

This study investigated the impact of pretreatment temperature on the dissolution of organic matter in sludge pretreated with alkaline rhamnolipid and its subsequent effect on the microbial community structure during anaerobic fermentation. The findings revealed that when the pretreatment temperature reached 80 °C, the maximum concentration of SCOD is 5008.89 mg/L, which is 4 times higher than that achieved at room temperature. Three-dimensional fluorescence parallel factor analysis indicated that increasing the pretreatment temperature significantly enhanced the degree of humification of sludge DOM and reduced the ratio of protein-like and fulvic acid in the sludge. The 16S rRNA gene-based analyses revealed that the relative abundance of Bacteroidetes was highest at 80 ℃ (11.14 %), and continued to increase as fermentation time progressed. This study highlights the critical role of temperature in the three-factor pretreatment of sludge, demonstrating that higher pretreatment temperatures not only accelerate the acid production rate during anaerobic fermentation but also enhance overall acid production.

Dynamics of humus in field crop rotations on drained lands

The purpose of the research is to study the influence of different types of field crop rotation, fertilizers, drainage and hydrothermal conditions on the dynamics of humus in reclaimed soil. The studies were carried out on the experimental fields of the All-Russian Research Institute of Reclaimed Lands (reclamation sites “Kuzminskoye Boloto 2”, “Semenovskoye” and “Gubino” in the Tver region). Waterlogged soils were drained using closed drainage (inter-drain distance is 18–20 m, drain depth is 0.9–1.2 m). The soils of the experimental plots are soddy-podzolic, light loamy, gleyic, formed on a moraine or thin binomial. Observations of the dynamics of humus were carried out in the grain-grass-row, grain-grass, grain and grain-row types of crop rotation. The influence of crop rotation on the content of humus in the soil was determined, first of all, by the composition, the structure of the crops grown and agricultural technology of their cultivation. Due to plant residues, 56.6–76.5 % of the volume of mineralized humus were restored in grain-grass-row crop rotation, 51.8 % in grain, 26.4 % in grain-row crop rotation. The most significant qualitative changes in the composition of humus were observed in grain-grass-row crop rotation: with a positive humus balance, the ratio of humic and fulvic acids increased from 0.63 to 0.74. The use of organic and mineral fertilizers significantly changes the balance of humus in the arable layer of the soil. With an organic-mineral fertilizer system, the annual loss of humus (in kg/ha) on the drained plot was 6.8–11.4 times less, on the non-drained plot – 2.1–2.6 times less than in the variant without fertilizers. Drainage of waterlogged soils increases the role of fertilizers in the accumulation of humus, reduces its losses and improves the quality parameters of humus – the ratio of humic and fulvic acids in the composition of humus under the influence of drainage increased from 0.61 to 0.88. The impact on the dynamics of humus of hydrothermal conditions has been established. In years with a dry first half of the growing season, an increase in humus content is observed; in excessively wet years, on the contrary, a decrease is observed. The correlation coefficients of humus content with hydrothermal conditions in May-June were – 0.84 (in 1985–1993) and 0.95 (in 2014–2022).

Different crystalline manganese dioxide and biochar co-conditioning aerobic composting: Reduced ammonia volatilization and improved organic fertilizer quality

Aerobic composting is a sustainable and effective waste disposal method. However, it can generate massive amounts of ammonia (NH3) via volatilization. Effectively reducing NH3 volatilization is vital for advancing aerobic composting and protecting the ecological environment. Herein, two crystal types of MnO2 (α-MnO2 and δ-MnO2) are combined with biochar (hydrochar (WHC) and pyrochar (WPC), respectively) and used as conditioners for the aerobic composting of chicken manure. Results reveal that α-MnO2 (34.6%) can more effectively reduce NH3 accumulation than δ-MnO2 (27.1%). Moreover, the combination of WHC and MnO2 better reduces NH3 volatilization (48.5–58.9%) than the combination of WPC and MnO2 (15.8–40.1%). The highest NH3 volatilization reduction effect (58.9%) is achieved using the combination of WHC and δ-MnO2. Because the added WHC and δ-MnO2 promote the humification of the compost, the humic acid to fulvic acid ratio (HA/FA ratio) dramatically increases. The combination of WHC and δ-MnO2 doubled the HA/FA ratio and resulted in a net economic benefit of 130.0 RMB/t. Therefore, WHC and δ-MnO2 co-conditioning can promote compost decomposition, improving the quality of organic fertilizers and substantially reducing NH3 volatilization.

Effects of land use and site on organic carbon fractions in some humic soil profiles of KwaZulu-Natal, South Africa

Soil organic matter (SOM) and its different carbon (C) fractions play a vital role in storing C and are a source of plant nutrients in natural and managed ecosystems. This study was conducted at six sites in KwaZulu-Natal Province to determine the effect of land use on the distribution of C fractions in selected humic soil profiles from different sites, using chemical and physical fractionation. Land use at some sites had been converted from natural grassland to maize and cultivated pasture and at others from native forest/wattle plantation to sugarcane farming. Humic acids (HA), fulvic acids (FA), hot water extractable C (HWEC), particulate organic matter C (POM-C) and mineral-associated organic C (MAC) were analysed to 1 m depth. Cropping lowered POM-C and HWEC, in the top 100 mm, irrespective of site differences, under pasture, grassland, forest and wattle plantation. Amongst the most labile fractions, FA predominated, resulting in a HA:FA ratio < 1 for pastures. The MAC was not affected by land use, irrespective of site differences. These findings reveal that organic carbon in humic soils can be decreased by cultivation but does not inevitably indicate the loss of C storage in the stable pool.

The Impact of Profile Genesis and Land Use of Histosol on Its Organic Substance Stability and Humic Acid Quality at the Molecular Level

This study is designed to evaluate soil organic matter (SOM) quality indicators: molecular indicators of dissolved organic matter (DOM) and hydrophobicity of humic acid (HA), distribution of quantity in humified and labile fractions of histosols during renaturalization. The aim is to determine the differences in the qualitative composition of humic acids at the molecular level, which are decided by the previous tillage and genesis, and to evaluate the impact of anthropogenization on the peat soil according to hydrophobicity, as well as to estimate the impact of soil genesis and removing peat layer. Soil samples were taken from the three Sapric Histosol (according to WRB2022) profiles and the 0–30 cm layer in three field replicates (Lithuania, Radviliskis mun.). Our study suggested that in the differently managed drained Sapric Histosol under renaturalization, the most significant changes occurred in the topsoil layer (0–30 cm), in which an increase in the content of SOM particles 106–2 µm in size. It is expedient to grow perennial grasses and legumes to maintain the soil organic carbon stability mobile humic acids to mobile fulvic acids ratio (MHA:MFA 0.83 to 0.86). An evaluation of the quality of HA (E4:E6) revealed their highest maturity in the unfertilized perennial grasses (3.88) and crop rotation (3.87) with grasses. The highest concentrations of hydrophilic groups (ratio of the C=O to O-H) were found in Sapric Histosol under deciduous hardwood forest (12.33). The lowest hydrophilicity (9.25 and 9.36) was of the crop rotation Sapric Histosol with removed peat layer. The most sustainable use of drained Sapric Histosol in the context of the sustainability and quality of its humus substances should be associated with the formation of perennial grass and clover grassland and the cultivation of deciduous hardwood. Therefore, the horizon forms on the top part of the profile, which protects deeper Histosolic material layers from its mineralization.

Time-dependent impact of co-matured manure with elemental sulfur and biochar on the soil agro-ecological properties and plant biomass

Farmyard manure is the most common type of organic fertilizer, and its properties depend mainly on the type of livestock, bedding material and the conditions of fermentation. Co-maturing of manure with other amendments to modify its final properties has been seen as a win–win strategy recently. This study aimed to evaluate the differences in the effect of unenriched manure and manures co-matured with biochar, elemental sulfur or both amendments on the soil physico-chemical and biological properties, and plant (barley, maize) biomass production. For this purpose a pot experiment was carried out in a time-dependent way. Samples were taken from 12 week-lasting (test crop barley) and 24 week-lasting (test crop maize) pot cultivation carried out in a growth chamber. Co-matured manure with biochar showed the highest rate of maturation expressed as humic to fulvic acid ratio, its amendment to soil significantly increased the dry aboveground biomass weight in the half-time (12 weeks) of experiment. However, the effect vanished after 24 weeks. We received for this variant highest long-term (24 weeks) contents of total carbon and nitrogen in soil. Contrarily, co-matured manure with biochar and elemental sulfur led to short-term carbon sequestration (the highest total carbon in 12 weeks) due to presumed retardation of microbial-mediated transformation of nutrients. We conclude that the prolonged pot experiment with biochar or elemental sulfur enriched manure led to the increased recalcitrancy of soil organic matter and retardation of soil nutrient transformation to the plant-available form.

Accelerating the humification mechanism of dissolved organic matter using biochar during vermicomposting of dewatered sludge

The use of biochar can accelerate the vermicomposting process of dewatered sludge. However, the underlying mechanism of vermicompost maturity with biochar is still unclear. This study investigated the effect of biochar on sludge maturation during vermicomposting by analyzing the spectroscopic characteristics of dissolved organic matter. For this, dewatered sludge mixed with and without 5 % biochar were separately vermicomposted. The results showed that the biochar could significantly increase the biomass of earthworms as well as the activity and abundances of bacteria and eukaryotes (P < 0.05) during vermicomposting of sludge. The addition of biochar resulted in a 23.35 % increase in the ratio of absorbances at wavelengths of 250 nm and 365 nm (E250/E365), and a 20.50 % decrease in aromatic proteins of sludge during vermicomposting, compared to the control. The ratio of fulvic acid to humic acid contents rapidly increased from 10 to 15 days in biochar added treatment, which was earlier than that in the control. Compared to control, the biochar addition enhanced the contents of fulvic acid and humic acid in sludge vermicompost by 79.97 % and 91.54 %, respectively. During vermicomposting, the DOM maturated parameter displayed stronger correlation (P < 0.05) between each other in the treatment with biochar, rather than the control. This study suggests that the biochar addition significantly modifies the degradation pathway of dissolved organic matter, thus promoting sludge maturation during vermicomposting.

PET addition delays the composting mature process and promotes microbiota associated with plastic degradation in plastisphere

Microplastics (MPs) enter forest and turf-grass and non-edible crops through sludge land reuse, thereby posing a major risk to human health and environmental security. MPs contamination can influence various biochemical processes by shifting microbial communities. However, the MPs effects in high-temperature sludge composting, as well as the microbiota associated with plastic degradation remain largely unexplored. Herein, we determined the effects of polyethylene terephthalate (PET) MPs on sludge-straw composting and microbial communities in 6 Biolan 220L composters for 50 days, using next generation sequencing technology. Our results showed that the humic acid to fulvic acid ratio (HA/FA) of PET treatment was lower (0.78) comparing to control, indicating that PET addition delayed the humification of composting. The Shannon indexes of the plastisphere were higher than surrounding compost and CK at the ripening phase (day 50), suggesting that MPs had a greater microbial enrichment. PET exposure altered the community composition, reduced the microbial network complexity, and decrease the relative abundance of thermophilic genus. Notably, several plastic degradation microbiota genera, including Brevibacterium, Halomonas and Aspergillus, were enriched in plastisphere, especially during the high thermophilic stage of sludge composting. There was a significant increase in the relative abundance of plastic degradation bacteria and fungi in plastispheres 0.38 ± 0.3% and 15 ± 6%, respectively, compared to those in the surrounding compost material. In summary, these findings indicate that plastisphere can accumulate potential microbiota associated with plastic degradation in high-temperature composting, which is beneficial to the development of future aerobic fermentation technology for MPs degradation.

Hydrothermal pretreatment and compound microbial agents promoting high-quality kitchen waste compost: Superior humification degree and reduction of odour

Present study investigated the effects of hydrothermal pretreatment (HTP) and addition of compound microbial agent (CMA) on humification, odour generation and metabolism functions of bacterial communities during composting of kitchen waste (KW). Surprisingly, HTP and CMA addition treatment could promote the humification of compost and the control of odour units in contrast to the control (without HTP and CMA addition). The humic acid to fulvic acid ratio of end compost increase by 187.30 %, while humification index (HIX) increased by 18.87 %. 3D-EEM fluorescence spectroscopy of dissolved organic matter (DOM) demonstrated that it facilitated the synthesis of humified compounds and the decomposition of biodegradable compounds. Moreover, the SUVA254, SUVA280 and E253/E203 increased by 118.6 %, 115.25 % and 42.11 % after HTP and CMA addition indicating an increase in aromatic carbon abundance. VFAs had the higher degradation rate (84.91 %) than other treatments (57.46–77.72 %). Meanwhile, the main contributor to the malodorous odour was isovaleric acid, followed by butyric acid and acetic acid during composting. Mantel test indicated that the humification degree was significantly influenced by environmental parameters (temperature, pH, etc.) and metabolic products (HA, DOC and VFAs). Metagenomic analysis indicated that the biodegradation processes at the thermophilic stage were controlled mainly through genes involved in microbial metabolism. HTP and CMA addition was an eco-friendly and efficient strategy to reduce odour emission and improve the compost quality.

Fluvisols Contribution to Water Retention Hydrological Ecosystem Services in Different Floodplain Ecosystems

Water retention is an important hydrological ecosystem service of active floodplain soils. The aim of the study was to evaluate the soil chemical, physical, and hydrological properties in Fluvisols in three different ecosystems that have an impact on water retention hydrological ecosystem services (WRHESs). We selected 16 localities along the Štiavnica River in Central Slovakia, 8 located in riparian zones (RZ), 5 in arable lands (AL), and 3 in grasslands (GL). Soil samples were collected from two layers (0–10 and 20–30 cm). In the laboratory, the soil physical (soil texture) and soil chemical properties (pH, soil organic carbon content, humic and fulvic acid ratio) were determined. Using undisturbed soil samples, the soil physical characteristics (particle density, bulk density, porosity, and actual soil moisture–SMa) were measured. With the help of pedotransfer functions, hydrological soil properties (field water capacity–FWC, wilting point–WP, available water capacity–AWC) were estimated. The recorded properties differed between the localities, ecosystems, and two layers. The SMa values showed a higher soil water retention potential of extensively used ecosystems, such as GL and RZ. However, the hydrological properties estimated by pedotransfer functions (FWC, WP, AWC) showed a higher soil water retention potential in AL localities. This indicated that for calculations, selected pedotransfer functions (particle size fractions, organic matter, and bulk density) and other soil or ecosystem properties (e.g., vegetation cover, meteorological conditions) have an impact on WRHESs. One such soil factor can be the quality of organic matter. On the basis of the results of the ANOVA, significant differences emerged between the different ecosystems for selected basic chemical, physical, and hydrological properties. The effect of the soil layer on the soil properties was revealed only in the case of SOC. The results indicated the effect of different ecosystems on soil WRHES and the importance of extensively managed ecosystems, such as RZ and GL. From this point of view, the reduction in the RZ and GL areas during a period of the last 70 years is negative. The findings should be taken into account in future sustainable floodplain management and landscape architecture.

Exploration of Fulvic Acid as a Co-Former in Crystal Engineering

The aim of the project was to investigate Peat-derived Fulvic acid for its propensity to form co-crystals with quercetin and curcumin and characterize it by using different analytical techniques. The formation of co-crystals generally enhances water solubility and the overall bioavailability of molecules. Co-crystals were synthesized using a 1:1 stoichiometric ratio of fulvic acid with quercetin and curcumin, respectively, using solvent crystallization techniques taking tetrahydrofuran and water in a 1:1 v/v ratio. The co-crystals were characterized by spectroscopic methods, FTIR and Differential scanning calorimetry. Further confirmation was made by morphological studies using SEM. A structural analysis was also carried out, using 13C solid-state NMR analysis. The studies confirmed the formation of semi crystalline forms. Furthermore, the saturation solubility displayed the enhancement in solubility of up to 10, 5-folds for Quercetin and Curcumin, respectively. The in vitro dissolution results showed that T50% was achieved within 30 min for both the drugs. The literature supports that the nutraceutical co-crystals offer advantages, particularly in the improvement of biopharmaceutical properties and addressing the challenges of the lab and manufacturing scale process. Both the semi crystalline powders exhibited enhanced solubility and a better dissolution profile.

Effect of the interaction of fulvic acid with Pb(II) on the distribution of Pb(II) between solid and liquid phases of four minerals.

Lead (Pb) is one of the top metal pollutants worldwide, and its distribution between liquid and solid phases of soils is strongly controlled by its adsorption on minerals, organic matter, and their composites. This paper presented the effect of fulvic acid (FA) coexistence on the distribution of Pb(II) at the solid-liquid interface of four minerals, which provided reference for how to use humic substances to remove toxic Pb(II) in soils. The free Pb2+ of suspensions, measured by Pb ion selective electrode, was used to characterize the complexation of FA with Pb2+ at various pH. The adsorption isotherms of Pb(II) by montmorillonite, kaolinite, goethite, and gibbsite with and without FA were studied with batch experiments. Results indicated that the free Pb2+ decreased and complexed Pb(II) increased with the increase of FA concentration in Pb(II)-FA solutions, whether the initial concentration of Pb(II) was 0.1 or 1mM. Pb2+ hydrolysis was low and the free Pb2+ concentration in pure lead solution without FA was generally unchanged with increasing solution pH at pH < 6.0. But free Pb2+ decreased with the increase of pH in the presence of FA, suggesting that the complexation ability of FA with Pb2+ increased with the increase of solution pH. The adsorption of Pb(II) by the minerals without FA followed the order: montmorillonite > kaolinite ≈ goethite > gibbsite at pH5.0. The Pb(II) adsorption by montmorillonite and kaolinite significantly enhanced with 1g/L FA, while significantly inhibited with 3g/L FA at low initial Pb(II) concentration. However, the effect of FA on Pb(II) adsorption by montmorillonite was greater than that of kaolinite, which was mainly related to the crystal layer structure, adsorption area, and cation exchange capacity of the minerals. The Pb(II) adsorption by goethite and gibbsite was significantly enhanced by the addition of both 1g/L and 3g/L FA, and the enhancement was more evident in goethite system. The effect of FA on the distribution of Pb(II) between solid and liquid phases of the minerals was determined by the factors such as the initial concentration ratio of FA to Pb(II), the adsorption capacity of minerals for FA, and the number of soluble complexes of FA with Pb2+. Therefore, the distribution of FA between solid and liquid of four minerals affected the distribution of Pb(II) between solid and liquid phases of the minerals greatly. The results can provide an important reference for understanding the distribution of Pb(II) and the dynamics and mobility of active components in polluted soils.

Effect of crop residue and fertilizers on humus fractions and rice (Oryza sativa) yield

An experiment was conducted during 2019–20 at the Research Farm of Dr. BSKKV, Dapoli, Maharashtra to study the effect of crop residues and fertilizers on humus fractions and rice yield in Alfisols. The study was conducted on ex situ incorporation of crop residue along with fertilizers and the results indicated that application of rice straw @2.5 t/ha + Ain leaf residue @2.5 t/ha along with 100% NPK was significantly beneficial for improving the content of soil humin, humic acid, fulvic acid and humic acid : fulvic acid (HA: FA) ratio and yield of rice. Crop residue and fertilizer management significantly improved the soil humin, humic acid, fulvic acid and humic acid: fulvic acid (HA: FA) ratio. Build-up of soil humus was due to the balanced application of crop residue along with fertilizers for developing bio-stability in soil which helps maintain soil health. In contrast, the application of 50%, 75% and 100% NPK alone did not gain optimum humus content in soil and yield of rice because of unbalanced use of fertilizers. Overall improvement in soil humus and yield of rice was observed by the integrated use of crop residue along with fertilizers in Alfisols.

Manure Maturation with Biochar: Effects on Plant Biomass, Manure Quality and Soil Microbiological Characteristics

Application of biochar and composts prepared from organic wastes as soil amendments has been recognized as a beneficial strategy to enhance soil fertility and crop production. However, the modification of manures with applied organic amendments such as biochar has not been well explained. Therefore, the preliminary study was designed to evaluate the impact of two doses of biochar (low 0.4 kg + 10 kg of manure and high 4 kg + 10 kg of manure) on the modification of resulting co-composted manure properties, and subsequently to evaluate the effect of matured manure amendment on the soil chemical and biological properties and plant yield in the pot experiment with barley (Hordeum vulgare L.). The following variants were tested: control, manure (M), manure + low biochar dose (M + LB), manure + high biochar dose (M + HB). Results revealed that, the M + HB significantly improved the co-composted manure properties as compared to control and M + LB, respectively. The most pronounced effects of M + HB treatment were observed on pH, NH4-N and humic acid to fulvic acid ratio (used as an index for manure maturity) relative to other treatments. Similarly, significant variations were observed between AOB (ammonium oxidizing bacteria) and nirs genes under M + HB which lowered the AOB and increased the nirs abundance as compared to other treatments. Moreover, when applied to soil, M + HB increased the observed soil chemical parameters with the exception of TN contents as compared to M and M + LB treatments. Similarly, plant biomass was significantly enhanced under the applied M + HB treatment. However, statistically insignificant differences were observed regarding soil enzyme activities and soil respiration values under the applied amendments. Thus, it was concluded that the co-composted manure with high biochar dose can have the potential to enhance the manure properties, soil fertilization value and plant biomass. However, its effects on soil microbiological and enzyme activities were intended be explored under long-term field experiments.

Physical and chemical properties of soils in Kharkiv (Ukraine).

The purpose of this work is to determine the physical and chemical properties of soils in different regions of Kharkiv (Ukraine) and to explore their impact on the sorption of heavy metal ions: Cu2+ and Zn2+. It has been established that the soils of gleyic chernozem and typical heavy black earth by their characteristics belong to highly buffer humified soils. According to the increase in the sorption capacity of the soil, it can be arranged in the following row: haplic arenosol < mollic gleyic fluvisol < gleyic chernozem < typical heavy black earth. The index of saturation with cations for typical heavy black earth is an order of magnitude higher than for the other studied soils. The distribution of mobile forms of copper and zinc in soils is determined by their type. The absorption capacity of the studied soils in relation to Cu2+ and Zn2+ directly correlates with a decrease in the pH of the soil solution, with the content of humus and with an increase in the carbon ratio of humic and fulvic acids. The materials of the research can be used to control the ecological situation in the city.

Biochemical Fulvic Acid Modification for Phosphate Crystal Inhibition in Water and Fertilizer Integration.

Biochemical fulvic acid (BFA), produced by organic wastes composting, is the complex organic matter with various functional groups. A novel modified biochemical fulvic acid (MBFA) which possessed stronger chelating ability had been synthesized by the grafting copolymerization of BFA and acrylic acid (AA). Results showed that MBFA effectively inhibited the crystallization of calcium phosphate and increased the concentration of phosphate in water solution. The optimum reaction conditions optimized by Box–Behnken design and response surface methodology were reaction temperature 69.24 °C, the mass of monomer to fulvic acid ratio 0.713, the initiator dosage 19.78%, and phosphate crystal-inhibition extent was 96.89%. IR spectra demonstrated AA was grafted onto BFA. XRD data and SEM images appeared the formation and growth of calcium phosphate crystals was effectively inhibited by MBFA.

E4/E6 ratio and total acidity of soil Humic and Fulvic acids from different land use patterns

Humic substances, the major fractions (nearly 85%) of organic matter, constituting humic (HA) and fulvic acid (FA) extracted from soils of different land use patterns viz., agriculture, forest, fallow, pasture, salt affected, horticulture and agroforestry land under varied agroclimatic zones of western Maharashtra (India) were evaluated for their individuality and properties through E4/E6 ratio and total acidity. Higher degree of aromaticity of HA was evidenced by lower E4/E6 ratio than FA in all the LUP. Soils from fallow land showed lower total acidity than forest. The distinctiveness of humic substances was influenced by land use management and climatic parameters (temperature and rainfall).

The Effect of Specific Soil Microorganisms on Soil Quality Parameters and Organic Matter Content for Cereal Production.

Soil chemical, biological and physical properties play important roles in soil quality and are related with increasing organic matter content, soil microbiological activity, plant nutrient content and availability. A new generation of soil amendments, containing specific soil microorganisms, are of great interest worldwide. Field experiments were carried out in 2018–2019 at the Institute of Agriculture, Lithuanian Research Centre for Agriculture and Forestry. The aim was to determine the impact of bio-products containing Trichoderma reesei, Acinetobacter calcoaceticus or Bacillus megaterium, and their mixtures on changes of soil organic carbon (SOC), soil respiration, and microbial biodiversity in loamy Cambisol. Under dry meteorological conditions, Trichoderma reesei, Acinetobacter calcoaceticus and Bacillus megaterium bio-products resulted an increase in SOC content, C/N ratio, humic to fulvic acid ratio, soil respiration, and microbial biodiversity. It is concluded that the use of a mixture of three microorganisms (Trichoderma reesei + Acinetobacter calcoaceticus + Bacillus megaterium) is the most promising bio-amendment under climate change. Future research is needed on different soil types and textures.

Probing changes in humus chemical characteristics in response to biochar addition and varying bulking agents during composting: A holistic multi-evidence-based approach

Despite the various benefits of humus, the changes in its chemical characteristics during composting in response to biochar addition and varying bulking agents remain to be further explored. In this study, three treatments were conducted, in which swine manure, bulking agent, and biochar were mixed at ratios of 4:1:0, 8:1:0, and 8:1:1. Fourier transform infrared spectroscopy (FTIR), carbon nuclear magnetic resonance spectroscopy (13C-NMR), three-dimensional excitation-emission matrix fluorescence spectroscopy (3D-EEM), and near-edge X-ray absorption fine structure (NEXAFS) were employed to characterize the chemical and structural properties of humus from multiple perspectives. The 3D-EEM spectra in this study showed a larger increase in humic acids (HAs) content (56%) and HAs to fulvic acids ratio (128%) during composting, indicating stronger humification in biochar-amended treatment. FTIR, 13C-NMR, and NEXAFS all confirmed the essential properties of HA as the core agronomic functional substance with rich aromatic and carboxyl groups, and that its aromaticity increased gradually during composting. In addition, 13C-NMR demonstrated that biochar addition and a relatively higher bulking agent ratio aided an increase in the carboxyl C proportion in HA after composting. In particular, NEXAFS revealed that biochar addition promoted the diversification of C, N, and O species in HA, with the emergence of quinone C and O-alkyl C as the main representatives. This work suggests that biochar addition and a relatively high bulking agent ratio could enhance humification and improve the agronomic function of humus.

Effects of microplastics on humification and fungal community during cow manure composting

The effect of microplastics (MPs) on the biological treatment of organic waste has been extensively studied, but little is known about the influence of different MPs on composting humification and the fungal community. In this study, PE, PVC, and PHA MPs were individually mixed with cow dung and sawdust and then composted. The results showed that different MPs had various influences on humification, and the humic acid to fulvic acid ratio of all MP-added treatments (0.44–0.83) was lower than that of the control (0.91). During the composting process, Ascomycota (26.32–89.14%) and Basidiomycota (0.47–4.78%) are the dominant phyla in all treatments and all microplastics decreased the diversity and richness of the fungal community at the thermophilic stage of composting. Exposure to MPs had an obvious effect on the fungal community at the genus level, and the addition of PHA and PE MPs increased the relative abundance of phytopathogenic fungi. LEfSe and network analysis indicated that MPs reduced the number of biomarkers and led to a simpler and more unstable fungal community structure compared to the control. This study has important implications for assessing microplastic pollution and organic waste disposal.