Organic Fraction Research Articles

Response of Runoff, Sediment Yield, and Runoff‐Related Dissolved Organic Carbon Loss to Variable Straw Mulching Rates on Sloping Lands of Regosols

ABSTRACTDissolved organic carbon (DOC), an organic carbon fraction with high activeness and mobility, migrated by runoff is a key part in carbon cycle. A rational straw mulching rate can be regulated to obtain maximum benefits while controlling runoff and sediment yield on sloping lands. However, little remains known about the optimal straw mulching rates required for effectively reducing the loss of DOC in runoff. Therefore, to overcome the existing limitations, this study investigated the effects of modified maize straw mulching rates on the loss of DOC during runoff, utilizing indoor rainfall simulation. Five mulching rates, including 0, 0.2, 0.4, 0.6, and 0.8 kg m−2 [control (CK) and treatments (T1, T2, T3, and T4), respectively], were tested in combination with three slope gradients (10°, 15°, and 20°) to evaluate how straw mulching rate influences runoff, sediment yield, and runoff‐related DOC loss under a heavy rainfall intensity of 90 mm h−1. Our results showed that various straw mulching rates did not significantly differ runoff rates; however, straw mulching significantly reduced sediment concentration and yield. Moreover, the reduction in sediment yield increased with an increase in mulching rate. Compared to the CK, T1 resulted in a 63% increase in DOC loss at a slope of 20°. Additionally, T2 caused an 8% and 7.2% increase in DOC loss at both 10° and 15° slopes. Conversely, T3 and T4 reduced DOC loss by 54.1%–80.8% and 51.1%–65.2%, respectively, across all slope gradients. These results suggested that mulching rates of 0.2–0.4 kg m−2 may potentially increase DOC loss in runoff on the sloping lands. Our results hold significant importance in optimizing the use of straw mulching for sustainable management practices in agricultural lands.

MiPrime: A model for the microbially mediated impacts of organic amendments on measurable soil organic carbon fractions and associated priming effects

Priming effects can influence the efficiency with which organic amendments sequester carbon in the soil. Yet, few soil models currently include priming effects. Those models that do are often based on operationally defined soil pools and implicitly allow only for positive priming effects. This limits the verification of model processes with experimental data and hinders the optimization of our carbon sequestration strategies. To address these shortcomings, we developed MiPrime, which offers a framework for the mechanistic modelling of organic amendment impacts on microbially mediated transformation of carbon fractions that are quantifiable through parsimonious soil extraction methods. MiPrime allows for assessment of organic amendment impacts on soil carbon dynamics, including priming effects, by simulating changes in mineralized, microbial biomass, dissolvable, hot water extractable and insoluble carbon fractions in soil exogenous (i.e. organic amendment-derived) and endogenous (i.e. soil) pools. After calibration of model parameters using Markov Chain Monte Carlo methods to incubation data of three types of isotopically labelled roadside grasses (a fresh grass product, a compost thereof, and a Bokashi-fermented product thereof), MiPrime was able to simulate changes in carbon fractions of the soil with a good degree of accuracy for five compositionally complex organic amendments, namely the three types of roadside grasses, as well as non-isotopically labelled wood chips and water weeds and reeds. Validation of the model results with experimental data demonstrates that changes in total carbon were very well predicted but that there is room for improvement in predicting mineralization rates and changes in dissolvable, hot water extractable and insoluble carbon fractions in the soil endogenous pool. MiPrime thus offers an initial step towards the mechanistic modelling of organic amendment impacts on measurable soil carbon fractions and can operate as a new tool for designing effective carbon sequestration strategies and understanding organic amendment impacts.

Experimental and performance analysis of organic fraction of municipal solid waste in downdraft gasifier

It is anticipated that the production of municipal solid waste will increase from 2.10 billion tonnes in 2023 to 3.80 billion tonnes by 2050. About 170 billion metric tonnes of biomass is produced worldwide each year. On a wet basis, the composition of municipal solid waste (MSW) includes approximately 20% of wood, 70% of food waste, 60% of yard trimmings, and 50% of other organic materials. Gasification of waste biomass is one of the most efficient processes for creating gaseous fuel and subsequently power with reduced environmental impact. The current work presents a novel strategy to reduce MSW by converting waste into briquettes and feeding it in gasifiers to produce syngas. The downdraft gasifier is employed in the syngas generation process. With a calorific value of 22.6 MJ/kg and a higher lignin concentration of approximately 31%, MSW proves to be suitable for thermochemical conversion processes. This article presents the results during gasification of briquette made from organic fraction of municipal solid waste (OFMSW) with significant heating value of 22.6 MJ/kg. The fuel produced by the gasifier has a heating value ranging from 920 to 1150 kcal/m3, making it clean-burning. Its primary components consist of 19% to 23% carbon monoxide and 17% to 21% hydrogen. This study offers a unique investigation into the gasification behavior of the organic fraction of OFMSW in a downdraft gasifier, with an emphasis on optimizing operational parameters and evaluating the yield and quality of syngas. Although gasification has been widely studied as a thermochemical conversion method for biomass, the specific performance of OFMSW in this process has received limited attention. By focusing on this underexplored area, the study enhances the understanding of OFMSW's potential in gasification and its contribution to sustainable energy production, thereby addressing key issues in both waste management and renewable energy generation.

Spatial patterns, source apportionment, and risk assessment of polychlorinated biphenyls (PCBs) in the surface sediments of eastern China lakes along a latitudinal gradient: Insights guided by full-congener analysis

Understanding the occurrence, sources, and ecological risks of polychlorinated biphenyls (PCBs), which are universal persistent organic pollutants, is critical for improving the sustainability and ecological safety of lake systems. Herein, to determine PCB contamination levels and formulate control strategies in lake sediments, 210 sediment samples were collected from 21 lakes along a latitudinal gradient (18–45°N, ∼3000 km) across eastern China and were analyzed for all 209 PCB congeners. The results showed that the total PCB concentration varied greatly from 0.26 to 163.82 ng/g dry weight and exhibited a latitudinal trend of central > north/south. Spatial variations were affected mainly by the organic carbon fraction and local population density. Most lakes had similar PCB profiles, with lower chlorinated PCBs dominating. Notably, non-Aroclor PCB 11 was the most abundant congener. Moreover, unintentionally produced PCBs (UP-PCBs) accounted for ∼31 % of all PCBs. These findings highlight that the significance of UP-PCBs has been overlooked in past studies and that full-congener analysis is necessary for future monitoring. According to the ecological risk assessment of PCBs, zero to moderate risk existed in lake sediments. Therefore, effective strategies are needed to mitigate the impact of PCBs (especially UP-PCBs) from multiple sources on lakes.

Innovative Circular Biowaste Valorisation—State of the Art and Guidance for Cities and Regions

The management of the organic fraction of municipal solid waste (OFMSW), also called urban biowaste, and urban wastewater sludge (UWWS) represents a challenge for cities and regions, which want to adopt innovative urban bioeconomy approaches for their treatment and production of high-added-value products beyond the traditional anaerobic digestion (AD) and compost. This adoption is often restricted by the availability and maturity of technologies. The research object of this manuscript, based on the findings of EU Horizon 2020 project HOOP, is the identification of state-of-the-art circular technologies for material valorisation of OFMSW and UWWS, following a novel screening methodology based on the scale of implementation (tested at least at pilot scale). The screening resulted in 25 technologies, which have been compared and discussed under a multidisciplinary assessment approach, showing their enabling factors and challenges, their current or potential commercial status and their compatibility with the traditional technologies for urban biowaste treatment (composting and AD). The bioproducts cover market sectors such as agriculture, chemistry, nutrition, bioplastics, materials or cosmetics. Therefore, the results of this review help project promoters at city/region level to select innovative technologies for the conversion of OFMWS and UWWS into high value products.

Effects of operational parameters on fuel gas production from DC-transferred arc plasma processing of sewage sludge

ABSTRACT In this work, a DC-transferred arc plasma reactor was used to investigate the influence of operating parameters on the process of gas production from sewage sludge treatment. By varying the operating temperature, feedstock feed rate and exhaust gas flow, the study aims to elucidate the physicochemical mechanisms during plasma treatment. The sewage sludge from the municipal wastewater treatment plant has an ash content of 40.5%, consisting mainly of Si, Al, Fe and Ca (>75%), and a complex organic fraction containing carbonyls, amines and amides. At a constant mass of feedstock (without feed rate), the gas produced by the plasma treatment was obtained with a maximum syngas fraction of 86% and a heating value of 10,000 kJ/m3, while the process operated at a constant sludge feed rate of 300 g/min increased the volumetric fraction of the syngas to 95% and the heating value to 12,000 kJ/m3.

Machine learning based prediction of biogas generation from municipal solid waste: A data-driven approach

This study aims to imply different machine learning (ML) (artificial neural network (ANN), linear regression, XGBoost, random forest (RF), support vector machine (SVM)) models to predict and optimize biogas production yield from organic fractions of municipal solid waste (MSW). The data set for six key input variables, including moisture content, C/N ratio, lignocellulose content and MSW age was analyzed and processed using ML models. Further, data exploratory analysis (EDA) analysis was performed using various steps such as data preprocessing, feature selection, train-test-validation splitting, model testing and evaluation. The results revealed that XGBoost and RF regression model exhibited superior performance efficacy. Both the models achieved a higher R2 values of 0.88 and 0.68, and low root mean square error (RMSE) values of 305 and 496, respectively. Furthermore, feature importance analysis was performed to identify the relative significance of input variables in biogas prediction. SVM model revealed significant contributions of moisture content (20.86 %), cellulose (60.21 %), hemicellulose (34.91 %), lignin content (62.84 %), and MSW age (17.23 %) in predicting biogas production. The findings of the study can be a resource for techno-crates/researchers to develop an efficient ML based decision-making tools for accurate predictions and process optimization.

Arbuscular mycorrhizal fungal inoculum and N2-fixing plants in ecological reclamation of arid mining areas: nutrient limitation of the moss biocrust microbiome.

Ecoenzymatic stoichiometry can reflect the ability of soil microorganisms to acquire energy and nutrients and to determine their response to environmental stresses. However, the drivers of metabolic limitation of the moss biocrust microbiome during the ecological restoration of coal mining areas are poorly understood. Therefore, in this study, enzymatic stoichiometry modeling and high-throughput sequencing were used to simultaneously determine moss biocrust microbial metabolic limitation and its relationship with moss biocrust nutrients and arbuscular mycorrhizal fungal (AMF) diversity in five arid and semi-arid revegetation types (Hippophae rhamnoides, Amorpha fruticosa, Cerasus humilis, Cerasus szechuanica, and Xanthoceras sorbifolium) and two microbial treatments (AMF-inoculated and uninoculated). The activities of moss biocrust carbon (C)-, nitrogen (N)-, and phosphorus (P)-acquiring enzymes and organic carbon fractions in the AMF-inoculated treatment were significantly higher than those in the uninoculated control. Moss biocrust microbial community C and P limitations were observed in the five revegetation types, with lower limitation in general in the AMF-inoculated treatment. Dinitrogen-fixing plants (Amorpha fruticosa and Hippophae rhamnoides) significantly mitigated moss biocrust microbiome C and P limitation, especially in the AMF-inoculated treatment. Furthermore, partial least squares path modeling (PLS-PM) shows that moss biocrust organic carbon fractions (- 0.73 and - 0.81 of the total effects, respectively) and AMF diversity (- 0.73 and - 0.81 of the total effects) had negative effect on microbial C and P limitation, suggesting that more efficient active nutrients and AMF diversity are important factors alleviating limitation of moss biocrust microbial metabolism. This indicates that moss biocrust microbial communities under N2-fixing species with AMF inoculation were more stable under environmental stress; thus, AMF inoculation and/or N2-fixing plants may be recommended as preferred options for the ecological restoration of arid mining areas.

Assessment of bi-metal paleo-redox proxies in the Bakken Formation black shales, Williston Basin, North Dakota, USA

The influence of paleoredox conditions and water-mass restriction on trace metal (TM) accumulation in the lower (LBS) and upper black shales (UBS) of the Devonian–Mississippian (D–M) Bakken Formation was assessed utilizing V/Cr, V/(V + Ni), Ni/Co, U/Th, and enrichment factors (EF) for Mo vs. U. These assessments were compared to previously published estimates based on degree of pyritization (DOPT), sulfur‑iron and C–S–Fe relationships, and sedimentological data. Bi–metal ratios suggest >80 % of samples were deposited under suboxic to anoxic/euxinic conditions, whereas DOPT results suggest >60 % of samples were deposited under dysoxic (0.42–0.75 DOPT) bottom–water conditions. DOPT results are in good agreement with C–S–Fe and total S vs. Fe assessments of paleoredox conditions and sedimentological evidence. Good agreement is also seen between Mo/TOC and Mo EF/U EF that both suggest the Bakken shales were deposited under a relatively unrestricted water mass conditions resulting in consistent renewal of TMs into the basin. With TM resupply outpacing drawdown, the basin could support enhanced primary productivity as well as high concentrations of TMs. Trace metal concentrations for the Bakken Fm. show considerable range for Co (0–10,324 ppm), Mo (0–2018 ppm), Ni (0–1574 ppm), U (0–1604 ppm), and V (0–3194 ppm), and bi–metal ratios for the Bakken Fm. are up to 5× greater than those reported for other D–M black shale formations. Bivariate and principal component analysis indicate Mo, Ni, U, and V accumulation was more closely associated with the organic fraction than with reducing conditions, thus accumulation of organic matter during deposition and generation, migration, and biodegradation of hydrocarbons during diagenesis may have influenced the accumulation and distribution of these TMs. Furthermore, changes in biogeochemical processes during the D–M transition may have fundamentally altered marine chemistry, with the evolution of vascular land plants and enhanced terrestrial weathering leading to an increased influx of nutrients into marine waters resulting in the Annulata, Dasberg, and Hangenberg black shale events. Factors controlling TM accumulation during time of deposition (e.g., TM availability, bottom-water redox conditions, adsorption onto organic matter) and during diagenesis and catagenesis (e.g., alteration and break down of organic matter, movement of fluid hydrocarbons or other basinal fluids) likely contribute to the lack of agreement between redox proxies, and subsequently, the lack of applicability of bi–metal ratios in assessing bottom–water conditions for the Bakken shales. Therefore, it is suggested that these bi-metal redox proxies are not an effective means to describe bottom-water conditions during the deposition of the Bakken shales.

Characterization of municipal solid waste with the perspective of biofuels and bioproducts recovery in Northeast Mexico

This work focuses on analyzing the physical composition of municipal solid waste (MSW) and the physicochemical characterization of the organic fraction of municipal solid waste (OFMSW) in a city in Northeast Mexico to propose an adequate treatment and valorization system. Diverse samples were analyzed over 5 months at the city of Saltillo landfill, where the daily discarded MSW was classified into household (HW), central market waste (CMW), and public areas and parks waste (PPW). For the HW and CMW, the fraction with the highest proportion was the organic residues from food products, with 22.15 and 25.78%, followed by other organic wastes (manure, yard waste, leaves, etc.) at 12.58 and 10.24%, respectively. Furthermore, the organic fraction was segregated from the rest of the MSW and classified into four subtypes, and their physical composition and physicochemical characteristics were determined. The results contribute to laying the foundations for the proper treatment of the OFMSW not just in the studied region but also in cities with similar conditions. Moreover, the OFMSW’s feasibility in treating via bioenergy technologies is revealed, and this research proposes a biorefinery treatment pathway through dark fermentation followed by high solids anaerobic digestion generating bioenergy and diverse bioproducts.

Influence of earthworms on the mobility and bioavailability of metals, metalloids and radionuclides in historically contaminated soil

While soil characteristics such as pH, cation exchange capacity and organic matter are known to influence the mobility of pollutants in soil and the transfer to vegetation, far less attention has been paid to the possible non-trophic influence of organisms on pollutant transfer to other species. When pollutants are present in a bound unavailable form in the mineral or organic fraction, they can be made available through bio-weathering and decomposition of organic material. Within this study, the impact of earthworms on the mobility of metal(loid)s and radionuclides in soil and their transfer to vegetation was evaluated and the pathways through which earthworms work were studied. Soil from a Belgian field, historically contaminated with metal(loid)s and radionuclides, was used and microcosm systems were applied to mimic the natural interactions between soil, earthworms (Lumbricus terrestris) and vegetation (Lolium perenne). Metal and radionuclide concentrations were determined in soil, pore water and grass. In addition, soil pH, (chromophoric) dissolved organic matter, the ionic composition of pore water and the soil microbial activity were analysed. In general, earthworm presence significantly increased the concentration of most pollutants in soil pore water. This could be a direct consequence of decreased soil pH and increased humification. The latter also lead to higher nutrient concentrations in pore water that were depleted in the root zone due to high accumulation by plants. Indications were found for earthworm-induced effects on the soil microbial activity. The results show that earthworm activity can increase leaching of metal(loid)s and radionuclides and enhance dispersion into the environment and transfer to other biota and the food chain. Biologically induced release or remobilization of pollutants in the soil should therefore be considered in the context of risk assessment and site management strategies.

Analysis of the Organic Chemical Fractions of Three Coal Extracts

Analysis of the Organic Chemical Fractions of Three Coal Extracts

Are bacterial communities and aggregation in fragile soils influenced by the management system?

Light-textured soils are widely distributed globally and, despite their limitations, have been integrated into agricultural production systems. This study aimed to assess how management systems—conventional tillage (CT) and no-till (NT)—affect aggregate formation pathways (physicogenic and biogenic) and bacterial communities. Two management systems (NT and CT) and three cover crops were evaluated: CJ: Crotalária (Crotalaria juncea (40 ​kg ​ha−1); M: Millet (Pennisetum glaucum - 60 ​kg ​ha−1); and C: Cocktail (Crotalária - Crotalaria juncea - 10 ​kg ​ha−1, Jack bean - Canavalia ensiformis - 75 ​kg ​ha−1, and Millet - Pennisetum glaucum - 30 ​kg ​ha−1). Undisturbed soil samples were collected from the crop row at a depth of 0.00–0.10 ​m. Aggregates with diameters between 9.7 and 8.0 ​mm were classified as biogenic or physicogenic. In addition to the chemical attributes of the aggregates, total organic carbon (TOC) and its fractions (mineral-associated organic carbon, MAOC; particulate organic carbon, POC; and free light fraction carbon, FLFC) were quantified. The structure and bacterial composition of the aggregates were also characterized. A higher proportion of biogenic aggregates (53–64%) was observed compared to physicogenic aggregates (36–47%). Cover crops exhibited significant differences in pH, calcium (Ca2+), base saturation, phosphorous (P), and percentage of base saturation. The management systems differed significantly for Ca2+ and P, with CT showing higher values than NT. The management system influenced organic matter accumulation and stabilization in the aggregates, with MAOC content being significantly lower in CT. POC and TOC were also significantly lower in physicogenic aggregates under CT. Bacterial community richness, diversity, and structure were significantly influenced by the management system, with greater richness and diversity in NT compared to CT. Network analysis revealed NT had more nodes and edges (65 and 406, respectively) than CT (52 and 357, respectively. Phyla abundance differed between the systems, with Firmicutes and Entotheonellaeota more abundant in CT, while WPS_2, GAL15, Bdellovibrionota, and Myxococcota were more abundant in NT. Despite the relatively short period of NT implementation (5 years), it had a positive effect on the bacterial community, which may subsequently influence nutrient and carbon content and their fractions in the aggregates.

Metabolic route and bacterial community changes induced by inactivation of indigenous bacteria in dark fermentation

Biohydrogen production by dark fermentation (DF) can be achieved using only indigenous bacteria from substrates or by adding an external inoculum. This study aims to provide new insights on the role of indigenous bacteria in DF process operation by investigating DF performances and microbiological aspects. DF tests are performed with only indigenous bacteria, with indigenous and exogenous bacteria and with only exogenous bacteria by inactivating indigenous bacteria by gamma irradiation. Sorghum irradiation reduces DF performances for both hydrogen (17.8 ± 12.8 versus 45.2 ± 1.7 mLH2/gVSadded) and total metabolite (0.22 ± 0.01 versus 0.30 ± 0.01 gCOD/gVSadded) yields. In contrast, no difference is observed with the organic fraction of municipal solid waste, suggesting a distinct role of indigenous bacteria for both substrates. Indigenous bacteria inactivation strongly modifies the metabolic routes and final bacterial community composition. This study proves the key role of indigenous bacteria in influencing metabolite production and bacterial composition.

Landfill Leachate and Coagulants Addition Effects on Membrane Bioreactor Mixed Liquor: Filterability, Fouling, and Pollutant Removal.

Urban wastewater (UWW) and landfill leachate (LL) co-treatment using membrane bioreactors (MBRs) is a valuable method for managing LL in cities. Coagulants can enhance the filterability of mixed liquor (ML), but the assessment of fouling is still needed. This research aimed to investigate the effects of co-treating synthetic wastewater (SWW) and real LL on an MBR, as well as the impact of adding poly-aluminum chloride (PACl) and Tanfloc SG. Cell-ultrafiltration experiments were conducted with four different feeds: synthetic wastewater, co-treatment with LL (20% v/v), and co-treatment with the addition of 30 mg L-1 coagulants (either PACl or Tanfloc). Co-treatment aggravated flux loss and reduced the recovery rate; however, Tanfloc and PACl improved recovery after cleaning (by 11% and 9%, respectively). Co-treatment also increased cake and irrecoverable/irremovable inorganic resistances, though coagulants reduced the latter, despite a lower fit of the Hermia models during the first hour of filtration. Co-treatment reduced the removal efficiencies of almost all pollutants analyzed, with the most significant impacts observed on the organic fraction. Coagulants, particularly Tanfloc, enhanced overall performance by improving flux recovery and reducing irreversibility, thus benefiting membrane lifespan. In conclusion, Tanfloc addition yielded the best results in terms of filterability and pollutant removal.

Mineralogy and geochemical controls on the distribution of REY-Ga-Se-Nb enrichment in the No. 6 Coal Seam, Soutpansberg Coalfield, South Africa

Coal is being explored as a potential alternative source for rare earth elements (REY + Sc), which are critical for advancing modern technology. Previous research has mainly focused on assessing the concentration and distribution of REY + Sc in coals from South Africa. However, the modes occurrence of these elements in coal is yet to be investigated. This study offers new insights on the mineralogy and inorganic geochemistry of the No. 6 Seam coal from the Soutpansberg Coalfield (South Africa). The objective is to investigate the distribution, enrichment, and modes of occurrence of critical elements such as Ga, Se, Nb, and REY + Sc within this coal. The No. 6 Seam is a medium rank-B, moderate vitrinite (avg. 41.5 vol%) coal, and contains major minerals such as kaolinite, quartz, and minor minerals including muscovite, siderite, dolomite, pyrite, and calcite. The total REY + Sc concentrations in the coal samples range from 79.9 to 332.1 mg/kg (avg. 213.2 mg/kg; whole-coal/rock basis), higher than global averages for hard coal. The upper continental crust (UCC) normalized concentration coefficients (CC) of the coal shows enrichment of La, Ce, Pr, Nd, Sm, Eu, Gd, Tb, Dy, Er, Yb, and Y. Distinct REY + Sc enrichment patterns are observed across different coal horizons, divided into two categories: light-REY (LREY) and medium-REY (MREY) in the bottom horizon coal [bottom-upper (BU) and bottom-lower (BL)], whereas the middle horizon coal [middle-upper (MU) and middle-lower (ML)] are enriched in medium-REY (MREY) and heavy-REY (HREY). The BU and BL samples show greater REY + Sc enrichment relative to the MU and ML samples. The samples also contain elevated concentrations of Ga (max. 106.1 mg/kg), Se (max. 50.9 mg/kg), and Nb (max. 14.8 mg/kg), exceeding the average values reported for Chinese coals.When considering the correlations between REY + Sc and major oxide elements, minerals, and organic petrographic assemblages, REY + Sc appears to be more closely associated with inorganic fraction, particularly aluminosilicate (such as kaolinite) and carbonate minerals (like dolomite), rather than with the organic fraction. The kaolinite and dolomite represent mostly detrital input and epigenesis, respectively. Gallium in the coal is primarily associated with aluminium oxide-hydroxide, Nb with minerals such as clay, rutile/anatase, and zircon; and Se with pyrite. Redox-sensitive elemental ratios of Al2O3/TiO2 andTiO2/Zr suggest that the detrital components of the No. 6 Seam coals were predominantly derived from a source consisting of felsic-intermediate rocks. These materials likely represent the weathering products of magmatic rocks from the passive-continental margin tectonic framework of the Limpopo Mobile Belt. Paleoclimatic conditions are inferred to be warm-humid to hot, with the peat deposited under suboxic-to-oxic environments. High values of critical REY percentage (REYdef,rel%: 29.85 to 39.75 %) and an outlook coefficient ≥ 0.7 suggest these Soutpansberg coal samples to be promising for REY + Sc recovery along with Ga.

Soil profile distribution of organic, inorganic, and labile carbon and nitrogen fractions vary in semi‐arid drylands under long‐term conservation tillage systems

AbstractChanges in soil carbon (C) and nutrients considerably influence soil health and agricultural sustainability. However, how agricultural management affects C and N allocation among various soil organic matter pools and their linkages with soil health are not clear for arid and semi‐arid regions. This study aimed to evaluate the soil profile distribution of selected C and N fractions and associated soil health properties in conventional tillage (CT), no‐tillage (NT), and strip tillage (ST) fields and quantify the relationship of labile and inorganic C and N fractions to soil organic carbon (SOC) sequestration in semi‐arid dryland cropping systems. Crop rotation was a 4‐year cycle of corn (Zea mays L.)—sorghum (Sorghum bicolor L. Moench)—winter wheat (Triticum aestivum L.)—fallow across all tillage systems. Soil samples were collected from 0–20, 20–40, and 40–60 cm depths of each plot in July 2022, after 9 years of plot establishment, and analysed for potentially mineralizable carbon (PMC), microbial biomass carbon (MBC), SOC, soil inorganic (SIC), soil total carbon (STC), soil inorganic nitrogen (SIN), total labile nitrogen (TLN), total organic nitrogen (SON), and labile organic nitrogen (LON) and other soil health indicators. The results indicate that PMC was 31% more and LON was 23% more in NT than in CT, whilst ST resulted in lower pH and had only 10%, 9%, and 24% more SON, STN, and LON, respectively, than CT in 0–60 cm profile. The SIC stock was negatively correlated with MBC, PMC, SON, STN, LON, TLN, and SIN, whilst positively correlated with depth, STC, and pH. After 9 years of conservation tillage, whilst depth‐wise distribution varied among tillage systems, soil C sequestration rate was negative in the 0–60 cm profile under both NT and ST compared with CT, mainly owing to more SIC accumulation in deeper depth of conventional system. These results show the complexity of soil C and N allocation under different tillage systems, with NT and ST supporting greater C and N storage in the surface soil and CT supporting more C and N storage in the deeper depth. Soil biological activity indicators appear to drive surface SOC accumulation, whilst soil pH and N availability influenced SIC accumulation in lower depths.

Effects of pyrolysis temperature on the photooxidation of water-soluble fraction of wheat straw biochar based on 21 ​T FT-ICR mass spectrometry

Biochar, formed through the pyrolysis or burning of organic wastes, has a complex chemical composition influenced by feedstock, pyrolysis temperature, and reaction conditions. Water-soluble, dissolved black carbon species released from biochar comprise one of the most photoreactive organic matter fractions. Photodegradation of these water-soluble species from wheat straw biochar, produced at different pyrolysis temperatures in laboratory microcosms, resulted in noticeable compositional differences. This study characterized water-soluble transformation products formed through the photodegradation of wheat straw biochar pyrolyzed at 300, 400, 500, or 600°C by electrospray ionization 21 ​T Fourier transform ion cyclotron resonance mass spectrometry (21T FT-ICR MS). We also evaluated global trends in the toxicity of these water-soluble fractions using MicroTox™ to assess the impacts of pyrolysis temperature. Additionally, we examined biochar surface morphology after photodegradation and observed minimal change after irradiation for 48 ​h, though the total yield of water-soluble biochar species varied with pyrolysis temperature. Trends in toxicity observed from MicroTox® analysis reveal that water-soluble photoproducts from biochar produced at 300°C and 900°C are nearly three times as toxic compared to dark controls. The ultrahigh resolving power of 21T FT-ICR MS allows for the separation of tens of thousands of highly oxidized, low-molecular-weight (<1 ​kDa) species, showing that photoproducts span a wider range of H/C and O/C ratios compared to their dark analogs. This study highlights the impacts of photodegradation on the molecular composition of water-soluble biochar species and underscores the influence of pyrolysis temperature on the quantity and composition of dissolved organic species.

Influence of soil organic carbon fractions on the soil priming effect under different vegetation restoration modes

AbstractThe soil priming effect is a key mechanism influencing carbon (C) cycling processes between the forest soil organic carbon (SOC) pool and the atmosphere. Different vegetation restoration modes have different SOC pool compositions, and it is not clear whether such differences affect the soil priming effect. Therefore, we selected soil from six typical vegetation restoration modes Platycladus orientalis (PO), Pinus sylvestris (PS), Quercus acutissima (QA), shrub (SH) and wasteland (WL) in the soil and rocky mountainous areas of northern China and measured the soil properties, microbial communities, microbial necromass carbon (MNC), SOC fractions and the soil priming effect. The SOC content decreased in the order of PO (21.33 g kg−1), PS (22.00 g kg−1), QA (13.67 g kg−1), SH (13.33 g kg−1) and WL (10.33 g kg−1), and the trends of the mineral‐associated organic carbon (MAOC) and fungal necromass carbon (FNC) content were the same as those of the SOC content. The soil priming effect was greater in both forests and shrublands than in wastelands, with the greatest effect occurring in PO forests, where the soil priming effect reached 159.91 mg CO2‐C kg−1 soil after 30 days of incubation, which was 1.4 times greater than that in WL. The soil priming effect was mainly determined by the difference in MAOC content. In addition, the soil C/N ratio and bacterial community diversity also indirectly affected the soil priming effect by influencing the soil MNC and SOC fractions. Overall, afforestation increased the SOC content, fungal necromass contribution and mineral conservation, increasing the soil priming effect. This theoretical foundation supports the enhancement of SOC sequestration capacity by implementing various modes of vegetation restoration in the future.

Cow dung compost and vermicompost amendments promote soil carbon stock by enhancing labile organic carbon and residual oxidizable carbon fractions in maize field soil

AbstractEnhancing soil quality and promoting the accumulation of soil organic carbon through economically and environmentally sustainable practices are essential for modern agriculture. This study aimed to investigate the effects of various organic amendments and rotation systems on soil properties and sweet corn growth in sandy loam soil. A split‐plot field experiment was conducted over 2 years, including rotations with or without Sesbania sesban as the main plot and six fertilizer treatments: a no fertilizer control, chemical fertilizer and four organic amendments as subplots. The cropping system did not significantly influence soil properties and sweet corn growth. However, the application of soybean meal, castor meal, cow dung compost and vermicompost resulted in sweet corn yields comparable to those achieved with the chemical fertilizer treatment. Notably, the soil organic matter (SOM) content was significantly higher in the cow dung compost and vermicompost treatments compared with both the no fertilizer and chemical fertilizer treatments. Moreover, these two amendments significantly increased soil carbon stock because of significant increases in labile organic carbon (TOC400) and residual oxidizable carbon (ROC) fractions in the maize field soil. A significant positive correlation was observed between fresh ear weight with husks and several soil parameters, including electrical conductivity, available P, exchangeable K and Zn, NO3–N, NH4–N, inorganic C and N, TOC400, ROC and SOM. In conclusion, cow dung compost and vermicompost not only result in sweet corn yields comparable to those from chemical fertilizer but also significantly enhance soil carbon stock by increasing TOC400 and ROC. Therefore, they can partially substitute for chemical fertilizers in promoting sustainable agricultural production of sweet corn.