Agricultural soils are a significant source of nitrous oxide (N₂O) emissions. The application of biochar to soil offers a synergistic approach to establishing stable organic carbon (C) storage while reducing greenhouse gas (GHG) emissions, particularly through effective reductions in N₂O emissions. However, current biochar application strategies often lack consideration of locally tailored application rates and biochar properties, limiting its N₂O mitigation potential. Here, we conduct a spatially explicit analysis to investigate the N₂O mitigation potential of straw-derived biochar in China’s croplands, exploring optimal application strategies under both ideal and realistic conditions. The key drivers that influence the spatial patterns of straw-derived biochar’s mitigation potential and application strategies are also revealed. We find that applying biochar with optimal strategies could avoid approximately 50% and 36% of nationwide cropland N₂O emissions under ideal and realistic conditions, respectively. The optimal biochar application rate and properties required to achieve the maximum N₂O reduction potential exhibit significant spatial variability, differing among biochar types. Key factors determining the optimal biochar application rate in various regions include N fertilizer application rates and soil organic carbon (SOC) content, while water input—including precipitation and irrigation water input—is the primary factor determining the optimal biochar properties. These findings may inform the development of site-specific biochar application strategies aimed at enhancing the N₂O mitigation efficacy in croplands across China.

Secretion and long-term accumulation of phenolic acid allelopathic substances are critical factors decreasing yield in continuous capsicum cropping systems. However, there are limited effective technologies and methods for removing these substances. In this study, biochar (BC) with ultrahigh specific surface area and pore volume was prepared via K₂CO₃ etching, called carbonate-modified biochar (CBC). Then, it was loaded with horseradish peroxidase (HRP) under glutaraldehyde crosslinking conditions to form HRP–CBC. The maximum loading capacity of HRP reached 311.46 U g⁻¹. Under various factors, the degradation efficiency of allelopathic substances such as ferulic acid followed the order HRP–CBC > HRP–BC > HRP, indicating that the combination of alkaline etching and enzyme immobilization enhances ferulic acid degradation. At a HRP–CBC dose of 2 U mL⁻¹ and pH 7, the degradation of 20 mg L⁻¹ ferulic acid was achieved within 6 h. Furthermore, this method demonstrated excellent degradation performance against multiple phenolic acid compounds responsible for yield reduction in continuous chili pepper cropping systems. HRP–CBC exhibited superior stability, enhanced stress resistance, and broad application potential. The inhibitory effect of ferulic acid on chili seed germination disappeared after degradation by immobilized HRP. Liquid chromatography–mass spectrometry and ecotoxicity analyses confirmed that HRP–CBC degraded ferulic acid into less toxic small organic molecules through a free radical-mediated mechanism. Therefore, a modified biochar immobilized with HRP offers a promising strategy for removing phenolic acid allelopathic substances from continuous cropping systems.

Engineered biochar has emerged as a versatile tool for purpose-specific rhizosphere engineering, offering tailored solutions for enhancing crop production, crop protection, and environmental remediation. Yet, its effectiveness depends on optimizing application for specific functional goals rather than adopting a one-size-fits-all approach. This review explores how engineered biochar shapes rhizosphere processes to support crop production, crop protection, and soil remediation. It examines key mechanisms including enhanced nutrient availability, stimulation of beneficial microbial communities, pathogen suppression, and soil contaminant immobilization, and how different biochar modifications, such as nutrient enrichment, antimicrobial functionalization, and surface engineering, drive these outcomes. The review highlights important trade-offs, such as the competing demands of nutrient availability for crop growth versus contaminant immobilization for remediation, and accounts for the spatial and temporal variability of biochar effects in the rhizosphere. While biochar presents clear synergistic benefits (e.g., improving soil structure, enhancing water retention, reducing greenhouse gas emissions, and enabling carbon sequestration), its practical application faces challenges related to competing objectives, rhizosphere complexity, and economic constraints. Emerging innovations such as nanocomposite biochars, bioprimed biochars, and biochar-microbe synergies offer new avenues for precision agriculture and sustainable land management. Finally, the review emphasizes the importance of long-term field studies to evaluate sustainability, and outlines opportunities for biochar in climate change mitigation, waste valorization, and agroecological resilience. By integrating the latest research on biochar’s mechanisms, challenges, and opportunities, this review provides a comprehensive framework for leveraging engineered biochar to address the pressing challenges of modern agriculture and environmental management.

As environmental pollution becomes an increasingly severe issue, the technology of enzyme immobilization on biochar has emerged as a promising solution for water and soil pollution remediation due to its efficiency, cost-effectiveness, and environmental friendliness. This review systematically examines the preparation methods, adaptation mechanisms, and applications of biochar-immobilized enzymes for pollutant removal. It focuses on the interaction between enzymes and biochar carriers, the selection of immobilization techniques, and the stability of immobilized enzymes. Biochar, as a carrier, offers advantages such as low cost, high specific surface area, and a variety of surface functional groups, which can be further enhanced through modification techniques to optimize its compatibility with enzymes. The review also discusses the strengths and weaknesses of various immobilization strategies, highlighting the high stability of covalent binding and the cost-effectiveness of adsorption methods. In the field of environmental remediation, biochar-enzyme composites have demonstrated synergistic effects in efficiently degrading organic pollutants, decoloring dyes, and remediating soil contaminants. While significant progress has been made in laboratory studies, the large-scale application of biochar-immobilized enzymes still faces numerous challenges, including raw material heterogeneity, enzyme deactivation, and ecological safety concerns. Future research should focus on developing intelligent design platforms, optimizing biochar-enzyme compatibility, overcoming the limitations of multifunctional synergistic remediation, and evaluating the long-term ecological impact. By integrating multiple technologies, biochar-immobilized enzymes hold great potential for widespread application in environmental remediation, advancing green and low-carbon technologies.

Soil organic carbon (SOC) decomposition is influenced by fluctuations in moisture levels, which play a crucial role in regulating global soil carbon balance. Biochar is widely used as an amendment to enhance carbon sequestration and soil health. However, the effects of biochar addition and moisture variability on SOC decomposition remain debated. Therefore, we conducted a microcosm incubation experiment to examine how moisture variability intensity and biochar addition affect SOC decomposition in an Alfisol topsoil from Northeast China. Our results show that increased soil moisture variability accelerates SOC decomposition by 0.5–17.2%, enhances total phospholipid fatty acid (PLFA) content by 29.9–39.6%, and raises the Gram-positive to Gram-negative (GP: GN) bacterial ratio by 2.1–11.0%. Additionally, moisture variability intensifies soil residual clay fraction particle content by 0.4–27.5%, contributing further to SOC decomposition. Biochar addition mitigates the impact of moisture fluctuations on SOC decomposition by stabilizing soil aggregates. These findings highlight the key roles of soil microbial communities and aggregate structure in governing SOC decomposition.

The design of phase-change renewable energy-harvesting materials has garnered increasing attention for achieving sustainable energy infrastructure and advanced applications. However, energy storage density that relies on the shape and crystallization of pristine phase-change materials (PCMs) usually lacks charge/discharge efficiency, and the inherent lattice defects in individual supporting scaffolds, further constrain their overall performance. In this study, lignocellulose-based biochar (obtained from spruce thermolysis at 600 °C) was assembled with an organically intercalated montmorillonite (MT) via modification and ultrasonication-assisted vacuum drying to produce engineered biomineral-based composite PCMs that simultaneously improve the latent heat and crystallinity of paraffin PCM. The biomineral hybrid was prepared using two preparation techniques: a conventional method of integrating biochar with clay mineral without intercalation, and a structural engineering approach involving the doping of cationic nanoclay into biochar. The engineered hybrid (EMB) achieved a 516.4% increase in surface area (9.9 m² g^–1 for bulk MT) and demonstrated a high PCM adsorption rate for hexadecane (C₁₆) with 223.3% enhancement in latent heat (15.7 to 121.3 J g^–1). The composite (EMB@C₁₆) also exhibited a 78% enhancement of thermal conductivity and charging/discharging efficiency. Moreover, EMB@C₁₆ retained over 95.9% of latent heat after 1000 cycles of heating (50 °C) and cooling (23 °C), with only a 4.1% reduction, providing continuous thermal energy supply during real-time temperature variation evaluations with thermal infrared imaging under both short and long cycle durations. This fabrication technique provides a rational approach for integrating naturally sourced and thermophysically reinforced biochar-based hybrids for advanced thermal regulation systems.

This study presents the development of a novel, disposable, and eco-friendly electrochemical device based on biochar-modified screen-printed electrodes (SPE/BC) for the detection of the antibiotic trimethoprim. Biochar, derived from sewage sludge, was applied as a nanomaterial to enhance the sensitivity of the sensor for trimethoprim quantification in environmental, biological, and pharmaceutical samples. Characterization techniques, including scanning electron microscopy, energy-dispersive X-ray spectroscopy, and Fourier transform infrared spectroscopy, were used to assess the properties of biochar. Surface area, pore volume, and pore diameter were measured using the Brunauer–Emmett–Teller method. The electrochemical sensor performance was analyzed using impedance spectroscopy, cyclic voltammetry, and differential pulse voltammetry, revealing a strong synergistic effect on the trimethoprim oxidation process. The device showed high sensitivity with a detection limit of 71.0 nmol L⁻¹ over a linear range of 1.75–231.43 μmol L⁻¹. Recovery studies in synthetic urine, tap water, and pharmaceutical tablets demonstrated recoveries of 92%–99%, with no sample pretreatment. The sensor exhibited selectivity towards common interferents such as sulfamethoxazole, urea, and ascorbic acid, making it a practical tool for detecting trimethoprim as an emerging pollutant.

Pyrolysis requires extensive experimentation to achieve optimum thermochemical conversion, which can be addressed by integrating machine learning (ML) predictive solutions. The abundant availability of algae with low volume footprint makes it viable green biomass to achieve thermochemical products. For optimum algal biochar (BC) yield production, the relation of ultimate, proximate analysis with process conditions is critical. This study’s objective is twofold: It aims to develop a robust ML model, trained on diverse literature data and optimized using particle swarm optimization and genetic algorithm, that predicts BC yield across various feedstocks and conditions. Secondly, the optimum process parameters are derived to maximize BC yield with the experimental validation for the collected samples at their respective chemical and structural compositions. Limited data points for algal biomass induce a comparative analysis of ML models, including Gaussian process regression, ensembled tree (ET), decision tree and support vector machine. The predictive capability of ET enhanced through optimization performed exceptionally well for BC yield prediction with testing R² = 0.77993 and RMSE = 6.9792. 2D and 3D partial dependence plots imply that BC yield is primarily influenced by pyrolysis temperature, volatile matter, and heating rate with SHAP values of 1.2785, 0.3972, and 0.2949, respectively. Monte Carlo simulation and Sobol sensitivity analysis substantiate statistically the impact of selected features on algal BC yield. Inverse optimization of ET model suggests that the maximum BC yield production is 76.33% at a temperature of 500 °C, a heating rate of 10 °C/min, a residence time of 60 min, a N₂ flow rate of 0.5 L/min, and particle size of 1.5mm.

Addressing the surging global energy demand while mitigating environmental degradation necessitates a paradigm shift from conventional energy systems to sustainable alternatives. However, the inherent intermittency of renewable energy sources mandates efficient harvesting mechanisms and advanced storage technologies to ensure uninterrupted energy availability. Thus, optimizing energy generation and storage systems is imperative for maximizing renewable energy utilization and advancing carbon neutrality. Biochar-based phase change materials (PCMs) emerge as a viable solution, simultaneously enhancing thermal energy storage efficiency and contributing to carbon sequestration. This study synthesizes biochar-based PCM composites using Neem (Azadirachta indica) seed-derived biochar, produced at two distinct pyrolysis temperatures (300 °C and 500 °C), and impregnated with lauric acid (LA). Comprehensive characterization through BET surface area analysis, FT-IR spectroscopy, SEM–EDS, DSC, and TGA evaluated the structural, chemical, and thermal properties of the composites. The biochar pyrolyzed at 500 °C exhibits a significantly higher surface area (668 m²/g), facilitating enhanced PCM loading. FT-IR analysis confirmed the successful impregnation of LA while preserving its molecular structure, while SEM analysis revealed a highly porous biochar network that optimizes PCM accommodation. DSC and TGA results demonstrated an impressive latent heat storage capacity up to 94.92 J/g, stable phase transition behavior, and improved thermal stability. Leakage tests and infrared thermal imaging further validated the composites’ shape-stabilizing efficiency, ensuring controlled heat absorption and dissipation without PCM leakage. By utilizing waste biomass, this study presents a sustainable and cost-effective approach to advanced thermal management, contributing to enhanced energy conservation and a reduced carbon footprint.

Living wall systems (LWSs) help to alleviate the climate and biodiversity harms associated with buildings and bring benefits to building occupants. Their performance can be variable and existing research points to the planting substrate as a key design factor. This study provides quantitative evidence on the physical, thermal and moisture performance of three planting substrates that vary according to the proportion of biochar added to green waste compost (GWC). Thermal conductivity (Wm⁻¹ K⁻¹), thermal resistivity (mK W⁻¹), volumetric moisture content (%) and mass (g) are measured for each fraction, replicated six times. Controlled drying procedures were employed, measuring these properties at a range of moisture levels. Data analysis finds that volumetric moisture content and biochar fraction have a statistically significant (p ≤ 0.05) effect on thermal conductivity. Added biochar is associated with non-linear reductions in thermal conductivity at low moisture levels. This suggests increasing the biochar fraction while reducing moisture in the substrate of a LWS will reduce its thermal conductivity, with a 100 mm planting substrate with 30% biochar and 30%vol moisture content providing 0.82 m² KW⁻¹ of thermal resistance, compared to 0.46 m² KW⁻¹ without added biochar. The methods build on previous work to assess the properties of different planting substrates for LWSs, providing a practical, lab-based assessment of biochar. The data produced are useful for researchers and professionals seeking to understand how biochar additions impact irrigation and thermal performance when specifying and designing LWSs and underline the potential value of biochar for improving the thermal performance of green infrastructure more widely.

Perfluorooctanoic acid (PFOA) has emerged as a new urgent pollutant in aquatic environments due to its high persistence and ecotoxicity. In photocatalytic degradation systems, challenges such as rapid recombination of electron–hole pairs (e⁻/h⁺), short lifespans of reactive oxygen species (ROS), and insufficient ROS generation hinder the efficient degradation of PFOA. This study presents a novel "scallop cage" architecture, constructed using Ulva biochar to create confined spaces that encapsulate the Fe₃O₄/ZnO heterojunction. This approach not only controls the crystal size of the Fe₃O₄/ZnO heterojunction but also confines the degradation reactions to a specific space, significantly shortening the mass transfer distance for ROS and effectively mitigating their rapid deactivation in aqueous-phase degradation processes. Furthermore, the confinement effect enhances the generation of multiple reactive species (·O₂⁻, ·OH, ¹O₂, and h⁺). The optimized FZS@UBC-2 composite photocatalyst achieved a PFOA removal efficiency of 97.53%. In practical applications, FZS@UBC-2 efficiently decomposes PFOA in complex aqueous matrices and can be easily recovered using an external magnetic field. This work not only expands the application of algae-derived biochar in advanced oxidation processes but also offers a sustainable strategy for addressing persistent organic pollutants in aquatic environments.

Engineered biochar with enhanced photochemical properties holds great potential for environmental remediation. However, natural humic substances, crucial players in environmental redox processes, are structurally complex and slow-forming, hindering mechanistic insights and practical applications. Here, we propose a co-engineering strategy that combines biochar with artificial humic substances synthesized from pine sawdust via controlled hydrothermal humification (180–340 °C). Modulating the hydrothermal temperature can yield artificial humic substances with diverse degradation degrees of lignin, yielding tailored phenolic architectures and electron-donating capacities (EDC). Using Ag⁺ photoreduction as a model reaction, we demonstrate that artificial humic substances produced at 340 °C exhibit optimal phenol content and the strongest reducing capacity (19.2-fold greater than that of substances synthesized at 180 °C). Notably, higher molecular weight fractions (> 5 kDa) of artificial humic substances were found to dominate Ag⁺ photoreduction due to their enriched phenolic content and superior EDC. Mechanistic investigations reveal that photo-excited phenolic groups generate superoxide radical (O₂^•−), initiating Ag⁺ reduction via a ligand-to-metal charge transfer (LMCT) pathway. Moreover, we discovered a previously overlooked phenomenon: hydrochar undergoes photo-induced dissolution, further enhancing photoreduction. This work provides new insights into the temperature-dependent lignin transformation into redox-active artificial humic substances and highlights the dynamic photochemical behavior of engineered biochar (hydrochar) under solar irradiation.

To address the urgent need to mitigate agricultural greenhouse gas emissions, research is investigating innovative strategies, including the application of biochar in various agricultural practices. Feeding biochar to cattle is an interesting strategy that not only aims to improve animal health and productivity, but can also have a cascading effect on soil improvement and CO₂ sequestration. Analysing the recovery efficiency of digested biochar and its structural integrity can provide insight into the potential of post-digestion biochar application. Here biochar quantification in dung is investigated for the first time using three different methodologies, namely thermal analysis, elemental analysis, and dichromate oxidation. Results indicate that a relative quantification within ± 1% biochar is possible. The majority of biochar (70–90%) fed to dairy cows survived digestion. The analysis further reveals selective preservation of the most stable condensed aromatic fractions of biochar during digestion, similar to short-term ageing in soil. The remaining digested biochar has an H/C ratio of 0.22 and an O/C ratio of 0.05, meeting the criteria for highly stable biochar. Our findings suggest that the digested biochar is highly suitable for long-term carbon sequestration when applied to soil via manure, offering a promising strategy for compensating agricultural greenhouse gas emissions.

Mounting global crisis including environmental degradation, resource depletion, and health threats, necessitates the exploration of various transformative, novel, and multifunctional materials with practical applications. Nanobiochar, a nanoscale biochar produced through pyrolysis and post-pyrolysis modifications, has emerged as a versatile and sustainable carbon-based nanomaterial with numerous applications. Biochar nanocomposites, engineered hybrid materials developed from biochar and nanomaterials, have further amplified the applications of biochar. Although the environmental applications of nanobiochar and biochar nanocomposites have been extensively studied, their potential applications in other critical sectors are less explored and not well understood. This review explores the potential applications of nanobiochar and biochar nanocomposites in the medical, energy, construction, polymer, and agriculture sectors. The unique properties of nanobiochar and biochar nanocomposites make them a promising candidate for healthcare applications, aligned with the One Health approach. In times of resource depletion and climate change, such composite materials show promise as a valuable resource for alternative energy storage solutions, sustainable construction, and climate-smart agriculture. However, further research is needed on the biocompatibility and extended ecotoxicity of these hybrid materials. The integration of nanobiochar and biochar nanocomposites in various domains and broadening their scope of application into underexplored sectors will address knowledge gaps and expand the use of emerging technologies for a sustainable and low-carbon future. This review underscores the need for more interdisciplinary research to fully leverage the potential of these composite resources and facilitate the transition to a more resilient and resource-efficient future.

Biochar is widely recognised as a carbon dioxide removal (CDR) technology, but its stability depends on feedstock, pyrolysis conditions, and the soil environment. Current CDR schemes prioritise highly stable biochars to ensure long-term permanence, requiring high pyrolysis temperatures that reduce carbon yield and intensify competition for biomass. This perspective explores potential synergies between two distinct CDR approaches, biochar application and peatland rewetting, where rewetted peatlands could enhance biochar permanence by suppressing microbial decomposition, offering a means to improve both carbon retention and resource efficiency. Using decomposition rate modifiers from biogeochemical models, we estimate biochar stability in rewetted peat and assess its CDR efficiency relative to a counterfactual of high-stability biochar application to dry soils. This perspective suggests that rewetted peatlands significantly reduce biochar carbon losses, particularly for lower-stability biochars, making them more viable for long-term CDR. By allowing greater flexibility in biochar selection, this approach could improve the scalability of biochar deployment while alleviating biomass supply constraints. While challenges such as land-use transitions and methane emissions must be addressed, integrating biochar with peatland rewetting presents a high-impact strategy to optimise the efficiency of biomass-based CDR.

A novel method for the preparation of a homogeneous Ni-doped microalgae-based biochar material Ni-f-BC was established by combining biological feed from marine microalgae with soluble nickel salts (at an optimized concentration of 40 mg/L NiCl₂) and successive carbonization with programmed temperature pyrolysis under N₂ flow. A uniform distribution of Ni with an average size of approximately 10 nm was identified by scanning electron microscopy (SEM), scanning transmission electron microscopy (STEM), and energy-dispersive X-ray spectroscopy (EDS) analyses. Successively, a biochar-coated electrode (Ni-f-BC/GCE) was prepared by the ultrasonic dispersion of the biochar in N-methyl-2-pyrrolidone (1 mg/mL) onto a glassy carbon electrode. A sensitive H₂O₂ sensor was developed based on our biochar materials with very good electrochemical performance, namely, with excellent electrocatalytic oxidation ability, a low detection limit of 0.39 μM in the physiological pH range (pH 7–8) and a rapid response time of 2.0 s. Notably, this sensor still exhibited good recovery rates of more than 90%, even in complex environments.

Phosphates are key contributors to eutrophication in water bodies. Lanthanum (La)-modified biochar (LaBC) offers notable advantages in achieving ultralow residual phosphate concentrations in water. However, the high cost of La limits its economic feasibility for practical use. This study applied machine learning (ML) models to optimize the design of La-based composite modified biochar, aiming to reduce application costs while maintaining effective phosphate removal to low residual levels. Eight ML models, namely random forest, gradient boosting regression (GBR), extreme gradient boosting (XGB), light gradient boosting, support vector machine, ridge regression, Bayesian ridge regression, and artificial neural network, were employed to predict the phosphate removal performance of La-based composite modified biochar. Results revealed that tree-based ensemble learning models (GBR and XGB: R²=0.98 and 0.99, respectively) outperformed other models. Feature importance analysis indicated that adsorption reaction conditions and metal loading were the primary factors influencing residual phosphate concentrations. Experimental validation demonstrated strong agreement between actual removal efficiencies and model predictions. Based on actual phosphate concentrations in various lakes, economic costs, and treatment effectiveness, targeted material remediation strategies were proposed. The phosphate removal costs for La–Fe-modified biochar and two types of La–Ca-modified biochar were reduced by 59.25%, 55.10%, and 76.54%, respectively, compared with that of LaBC, achieving dual optimization of treatment effectiveness and economic cost. Overall, this study provides insights into developing low-cost, high-efficiency biochar materials and offers robust technical support for controlling water eutrophication.

The development of metal-free catalysts for efficient selective catalytic oxidation of hydrogen sulfide (H₂S-SCO) to elemental sulfur represents a sustainable solution for toxic gas purification. Herein, we synthesized a regenerable metal-free catalyst through facile activation and pyrolysis of coffee grounds. The optimized catalyst demonstrated exceptional H₂S-SCO performance at 180 ℃, achieving>99% H₂S conversion with near-perfect sulfur selectivity (~100%) while maintaining remarkable stability under humid conditions and high CO₂ concentrations. These superior properties originate from the synergistic effects of elevated nitrogen doping (17.33 at.%), abundant defect edge sites, and hierarchical porosity. Density functional theory (DFT) calculations revealed that carbon atoms adjacent to pyridine-N configurations serve as dual-active sites, facilitating H₂S adsorption/dissociation and O₂ activation through optimized electron redistribution. A plausible reaction mechanism was established based on experimental and theoretical analyses. This work provides fundamental insights into designing cost-effective, biomass-derived carbon catalysts for industrial gas purification while addressing agricultural waste valorization.

Biochar is suggested to enhance the phytoremediation of cadmium (Cd) via regulating the rhizosphere environment and plant traits in contaminated soil. However, the effect of phosphorus (P)-modified biochar, the rhizosphere effect, and their interaction in improving phytoremediation efficiency of Salix for Cd remains unclear. Here, the effects of bamboo biochar, phytic acid-modified biochar, and sodium phytate-modified biochar on soil properties, the microbial community, plant traits, and Cd accumulation of Salix J1010 in Cd contaminated soil were comparatively and systematically studied. P-modified biochar significantly increased plant growth, Cd accumulation, and its translocation from roots to the aboveground parts of Salix. Cd concentration, root biomass, net photosynthetic rate, and rhizosphere microbial community variations were identified as critical predictors for phytoremediation efficiency using random forest models. Rhizosphere bacteria were more influenced by biochar amendment, while the fungi were more influenced by the rhizosphere effects. A key bacterial cluster, with a preference for high soil carbon and P, was further found to stimulate root growth and improve the bioavailability of soil Cd. Collectively, the study revealed differentiated responses of bacteria and fungi to biochar and rhizosphere effects of Salix, highlighting the importance of biochar modifications to optimize microbial interactions and enhance the phytoremediation efficiency of Salix in Cd-contaminated soils.

Biochar has emerged as an environmentally sustainable material for addressing agri-environmental issues owing to its porous structure, versatile surface chemistry, and stability. While pristine biochars have demonstrated effectiveness in various applications, ranging from agricultural soil enhancement to contaminant immobilization, their performance is often constrained by insufficient reactivity and limited selectivity. This review begins by outlining the biochar production process, emphasizing how key factors influence its physicochemical properties and overall performance. A major barrier to practical deployment is the difficulty of recovering fine biochar particles from treated media, often requiring energy-intensive methods, which limits the scalability for agri-environmental applications. To overcome these constraints, the review explores various biochar modification methods, focusing on magnetization and mineral impregnation techniques. As such, magnetic biochars (MBCs) not only retain the adsorptive benefits of carbonaceous materials but also enable facile recovery via external magnetic fields, addressing a major obstacle in post-treatment separation. In addition, the mineral doping of MBCs further enhances surface functionality and reactivity, improving removal efficiencies for a wide spectrum of pollutants. This review critically explores the synthesis routes, structural characteristics, and functional performance of magnetized and mineral-enriched biochars, with an emphasis on their applications in environmental remediation and soil enrichment. Mechanistic insights into adsorption pathways including pore-filling, electrostatic binding, and surface complexation are detailed, along with emerging approaches involving light-assisted degradation pathways. By synthesizing laboratory findings and field-scale observations, this review identifies current improvements and limitations, and outlines key directions for future research toward the practical and scalable use of engineered biochars for more sustainable agri-environmental applications.

Co-application of biochar with other amendments is generating interest as a means to increase biochar effectiveness for improving soil health. Yet, the extent to which such co-application improves soil health is unclear. This paper (i) synthesized the impact of biochar applied with or without organic and inorganic amendments on soil health indicators including soil physical, chemical, and biological properties using field studies, (ii) discussed potential factors that may affect the performance of the co-application, and (iii) summarized research needs. Based on 28 peer-reviewed publications up to September 30, 2024, biochar co-application improved 9 of 16 soil properties compared to biochar alone. It enhanced wet aggregate stability in 5 of 9 comparisons by 45%, saturated hydraulic conductivity in 5 of 6 by 17%, field water content in 8 of 14 by 20%, cation exchange capacity in 9 of 17 by 58%, and organic matter concentration in 5 of 9 by 37%. Also, co-application of biochar increased soil microbial biomass C, phosphatase activity, and N and P concentrations by 33% to 76% in most comparisons. However, it had mixed effects on bulk density, pH, electrical conductivity, C and K concentrations, as well as urease and dehydrogenase activities. Biochar co-application with organic amendments (compost/manure) improved soil physico-chemical properties (bulk density, C, N, P, K) more consistently than with inorganic amendments (NPK). The benefits of biochar co-application increased with higher application rates. These findings suggest that biochar co-application can improve selected soil properties more than biochar alone, with benefits for soil structure, water retention, nutrient availability, and microbial activity, though results for some properties remain inconsistent. Long-term studies (>5 years) across diverse soils and climates are needed to further elucidate these effects and optimize biochar co-application strategies for sustainable soil management.

Highlights

The agricultural sector urgently requires scalable solutions to reduce greenhouse gas (GHG) emissions from residue management. Biochar offers a promising carbon removal pathway, but its adoption is limited by technical, regulatory, and economic barriers. A key constraint is the lack of system designs that can accommodate multiple feedstocks while complying with land application regulations. This study designs and evaluates an integrated biochar production system that enables the separate processing of straw and manure through parallel pyrolysis lines, while optimising internal energy use. Environmental and economic assessments were conducted using a case study of the University of Leeds Research Farm, under a cradle-to-grave system boundary. The results show that the system can produce 300 t of biochar annually, sequester 350 t CO₂e, and reduce manure management emissions by 75%, with an additional 30 t CO₂e avoided through surplus heat utilisation. The carbon abatement cost is estimated at £226 per t CO₂e, primarily driven by capital (38%), operational (32%), and electricity (30%) costs. Sensitivity analysis highlights that straw availability, determined by both yield and crop rotation, is the primary factor influencing system performance. Among the mitigation strategies for addressing heat shortfalls, procuring external straw is identified as the most effective option. This study presents a novel and adaptable system framework for on-farm biochar deployment, addressing key barriers to implementation. The findings provide quantitative insights into the trade-offs between cost, carbon removal, and design decisions, and offer a foundation for scaling biochar use across the agricultural sector.

This study developed phosphorus-modified biochar (BCP) and phosphorus-magnesium co-modified biochar (BCPM) to improve nitrogen retention and humification during composting. Systematically, this study elucidated the synergistic biotic-abiotic mechanisms by tracking nitrogen transformation, fluorescence spectral dynamics, functional genes and microbial succession. Results demonstrated that compared to conventional biochar (BC), the BCP/BCPM immobilized NH₄⁺ via an abiotic pathway (surface adsorption and struvite crystallization), mitigating NH₃ emissions by 21.29–27.99%, while upregulating nitrification genes (amoA, hao, nxrA) and enriching functional consortia (Bacillaceae) to enhance total nitrogen retention (by 3%) through a biotic pathway. The biotic-abiotic synergy elevated the humification index (P_V,n/P_III,n) by 24.01–33.61%. The potential mechanism might be that a nitrogen retention supplied nitrogen skeleton and nitrogenous precursors for aromatic condensation reactions. Moreover, the enriched functional microbiota (Thermobifida) drove lignin degradation and protein-like conversion, redirecting toward precursors to stable humic-like substances. The phosphorus mainly mediated and enhanced the humification process (+7.74% vs. BCPM), while magnesium synergistically reduced more NH₃ emissions (–8.51% vs. BCP). Therefore, based on the phosphorus-magnesium co-modified biochar, increasing the phosphorus content loaded on biochar offers greater potential for humification. The spatiotemporal coordination of abiotic mineral interactions and biotic microbial specialization enabled simultaneous nitrogen retention and humification in composting.

Biochar amendment impacts soil water movement through modifications of soil properties, yet the mechanisms linking these changes to hydrological dynamics in vegetable soils with phosphorus (P) surplus remain elusive. This study systematically compared the effects of two regionally prevalent biochars—rice husk biochar (RHB) and palm silk biochar (PSB)—on water infiltration and leakage in a P-enriched sandy loam vegetable soil from southern China using a soil column experiment. Biochars were incorporated into the topsoil (0–20 cm) at rates of 0%, 3%, and 6% (w/w). Results demonstrated that RHB, with a broader pore size distribution and significant macropores (>50 nm) despite an average pore diameter of 40.7 nm, inhibited water infiltration more effectively than the uniformly mesoporous PSB (average pore diameter: 4.40 nm), especially in the surface layer. At the 6% amendment rate, RHB increased saturated water content (θ_s) by 14% and reduced saturated hydraulic conductivity (K_s) by 52%, whereas PSB delayed water release through mesopore-dominated retention. Both biochars comparably suppressed water leakage at a given amendment rate. Structural equation modeling quantified a dual regulatory mechanism: total organic carbon (TOC) governed infiltration by enhancing θ_s, while pH controlled it by reducing K_s. This synergy intensified the trade-offs between water retention and infiltration suppression at higher amendment rates. Although 6% RHB amendment (theoretical scaling: 186 t ha⁻¹) maximized hydrological benefits, the 3% amendment rate (theoretical scaling: 93 t ha⁻¹) offers a more practical, cost-effective balance for reducing water and dissolved reactive P losses. We conclude that biochar’s feedstock-specific pore structure (macropore-dominated RHB vs. mesopore-dominated PSB) and induced physicochemical changes (TOC-driven θ_s increase and pH-mediated K_s reduction) synergistically dictate hydrological regulation. This mechanistic insight optimizes water-P coordination in subtropical vegetable soils (e.g., Olsen-P>40 mg kg⁻¹, a threshold far exceeding the agronomic requirement and indicating a high risk of P leaching).

Biochar, a carbon-rich material with a porous structure, holds significant potential for mitigating climate change through carbon sequestration. However, its widespread adoption has been hindered by high production costs, primarily associated with oxygen-restricted systems and energy-intensive production processes. This study introduced a cost-effective, field-adapted strategy to enhance carbon retention in biochar derived from Litchi branches through limewater coating and synergistic water-fire interaction. Litchi branches were pretreated with limewater to create a surface coating, then underwent in-situ carbonization via self-oxygen-limited pyrolysis to form a dark-red char which was then quenched with limewater to produce biochar. Calcium (Ca)-mediated carbon retention during pyrolysis was investigated through Fourier-transform infrared spectroscopy (FTIR) coupled with scanning electron microscopy and energy-dispersive spectroscopy (SEM–EDS). The limewater-treated biochar achieved a significantly improved carbon conversion rate (86%) compared to CK (52%), the untreated biochar sample, with an enhanced specific surface area of 280 m² g^–1. FTIR and SEM–EDS analyses revealed that the limewater treatment formed a calcium-enriched protective barrier that effectively suppressed the formation of CO_x during combustion. Additionally, mineral Ca-carbon composites formed during pyrolysis further improved carbon stabilization and retention. This study offers a practical and scalable solution for producing biochar under field conditions by addressing challenges related to cost-effectiveness and process efficiency, thereby promoting the application of biochar for carbon sequestration.

In the context of carbon neutrality targets, biochar is widely promoted as a soil amendment to sequester organic carbon in soils. Although a wealth of research has illustrated the benefits of biochar to plants, its potential toxicity to soil fauna and microbes requires serious consideration. The aim of this study was to perform a meta-analysis of experimental data on biochar effects (i.e. percentage change in endpoints after biochar application compared to the control group) on plants, animals, and microorganisms. The experimental data were extracted from 61 papers and consists of 1329 data points. In a next step, machine learning was used to develop a classifier to predict, whether biochar has positive or negative consequences on soil organisms based on biochar and soil properties. The meta-analysis shows that the effect of biochar is negatively correlated with the biochar application rate, biochar pH, pyrolysis temperature, and soil pH. A random forest classifier was then developed to classify whether biochar was “beneficial” or “hazardous” based on four types of descriptors: biochar properties, soil properties, test organism, and endpoint type. The accuracy of the best model achieved an R² of 0.79. In the next step, a quantitative model was developed to predict the effect with an R² of 0.48. The model is of great significance for understanding the role of biochar in soil and improving the quality control strategy for biochar production.

Pyrogenic carbon (PyC) possesses electron transfer and exchange capabilities that can facilitate redox reactions in various geochemical and biochemical processes. The long-term environmental persistence of PyC makes it susceptible to substantial alterations in its physical and chemical properties through aging. However, there is a lack of research on how aging impacts PyC’s electron transfer and exchange properties. This study investigated the effects of aging on PyC samples derived from four feedstocks and prepared at two different pyrolysis temperatures. Three aging methods, including chemical aging, freeze–thaw cycling, and natural aging over a year, were employed. The results indicate that aging significantly enhanced the conductivity of certain PyC samples produced at 350 °C by more than three orders of magnitude, potentially attributed to the enrichment of redox-active functional groups. Conversely, for PyC produced at 750 °C, aging damaged the polyaromatic carbon matrices, resulting in reduced conductivity. Aging was found to decrease the electron-donating capacity (EDC) while increasing the electron-accepting capacity (EAC) of PyC produced at 350 °C, primarily due to a reduction in electron-donating C–OH groups and an increase in electron-accepting O–C=O groups. These findings shed light on the aging effects on the electron transfer and exchange properties of PyC and offer valuable insights for assessing PyC’s role in biogeochemical processes.

Phosphorus-modified biochar (3K-BC) was prepared from Salvia miltiorrhiza dregs via phosphate modification and applied for lead (Pb) and cadmium (Cd) removal from aqueous solutions and soil. The successful incorporation of orthophosphate into the biochar was confirmed by ³¹P NMR and other analytical techniques. Solution-based experiments showed that 3K-BC followed pseudo-second-order kinetics and best fitted the Langmuir isotherm model, indicating multiple chemical adsorption processes. The maximum adsorption capacities for Pb and Cd were 361.82 and 123.03 mg g⁻¹, respectively. The adsorption mechanism involved physical adsorption, precipitation, complexation with oxygen-containing functional groups, and cation exchange. Soil experiments demonstrated that 3K-BC significantly reduced heavy metal (HM) bioavailability, with greater reductions at higher application rates. Speciation analysis revealed a decrease in the acid-soluble fraction of Pb and Cd, while their stable, residual forms increased, effectively reducing metal mobility. Further confirmation was obtained through pot experiments, which showed that the application of 3K-BC increased the yield of Ligusticum chuanxiong by 61% and promoted its growth. In addition, the concentration of ligustilide increased from 24.24 to 29.63 mg g⁻¹. Under the condition of HM pollution, the total effective components of Ligusticum chuanxiong in the experimental group increased by 22.1%. This study provides a simple and effective strategy for remediating Pb- and Cd-contaminated water and soil while simultaneously recycling agricultural waste, thereby serving a dual purpose.

Highlights

Photofermentative biohydrogen production (PFHP) is a promising route for sustainable biohydrogen production, but its efficiency is constrained by inefficient intra/extracellular electron transfer (IET/EET). Biochar (BC) provides unique characteristics to enhance IET/EET in biochemical systems; however, non-conductive polymer groups hinder its charge transfer efficiency. The present study proposes the engineering of the microbial-electrochemical interface through dual metal (Co and Fe) functionalization of BC to improve charge transfer within the fermentative medium, thus leading to an increase in hydrogen production. SEM, BET, XPS, and Raman spectroscopy demonstrated that Co-Fe/BC functionalization results in 22.83% higher porosity and surface area compared to pristine biochar (PBC) and single metal functionalization, suggesting increased electrons from surface defects like oxygen vacancies (OVs). The optimal loading concentration (20 mg/L) of Co-Fe/BC enhanced the biohydrogen production rate and yield by 101.61% and 103.11%, respectively, exceeding the control group (CG). Electrochemical studies showed that the lowest interfacial charge transfer resistance (1.74 Ω, 1.22 mA redox current) in Co-Fe/BC increases charge transfer capabilities by 106.77% compared to PBC (4.66 Ω, 0.59 mA redox current) thus serving as an electron shuttle to increase redox sites through flavin and c-cytochrome. IET/EET enhancement in a bioreactor loaded with Co-Fe/BC regulates butyric acid to acetic acid metabolism, as revealed by microbial community analysis, where Clostridium was 86.72% more prevalent than CG (79.77%). This work demonstrates that Co-Fe functionalized BC not only bridges electron transfer bottlenecks but also provides a conductive interface for sustained microbial-electrochemical interactions, offering a scalable strategy for optimizing renewable biohydrogen production.

An innovative approach to providing a sustainable functionalization of biochar via amidation by mechanochemical route in the presence of octadecylamine is presented in this study. The proposed procedure is an attractive, cost-saving, and scalable alternative to the conventional approach meeting environmental sustainability expectations. The material obtained is widely characterized through spectroscopic and morphological techniques, confirming the presence of amide functional groups and ruling out simple amine sorption onto the carbon surface. As the long alkyl chains are introduced onto the biochar, an increase in hydrophobicity is induced, attributed to the exposure of hydrophobic groups and the increase in surface roughness, resulting in a new material for water-repellent coatings on hemp fibers. As a result of dip coating, the coated hemp fiber becomes hydrophobic with an angle contact value of 126° after a single deposition layer of biochar. Moreover, the biochar-coated hemp fibers showed a noticeable capacity (up to 1400%) to absorb several oils (frying, motor, pump, and sunflower) from an emulsion solution.

Biochar is increasingly studied as a potentially carbon-negative material that can also capture and sequester carbon dioxide (CO₂) from air or from a CO₂ stream. Physisorption of CO₂ is identified as the dominant process of CO₂ capture in biochar; it is also widely accepted that micropores play the main role in capturing and storing CO₂ molecules, whereas mesopores and macropores play a secondary role of providing a passageway for CO₂ molecules. This study aims to critically revisit the roles of mesopores and macropores in CO₂ capture. The research objectives include proposing improved mathematical models for calculating fractal dimensions for micropores, mesopores and macrospores in sawdust and biochar samples produced at different temperatures (300 °C, 500 °C, 700 °C, and 1000 °C); the CO₂ capture capability of these sorbents was then correlated with and predicted from their fractal dimensions, pore volume, pore area, pore diameter/width, permeability, and porosity. For mesopores/macropores, the improved fractal dimension model expressed the mercury contact angle on the sorbent pore wall with respect to the surface area covered by mercury. For micropores, the improved model describes the CO₂ adsorption cross-section of the sorbent within the formulation of the Brunauer–Emmett–Teller (BET) theory. It was found that these two models provided more physically realistic values for fractal dimensions (between 2.81 and 3.00) for all the sorbents, compared to existing models. The correlation between CO₂ capture capability and mesopore/macropore permeability (R² = 0.7148) is lower than the correlations with total pore volume (R² = 0.7894) and fractal dimension (R² = 0.7433). Multiple linear regression analyses also showed that only total pore volume and porosity are statistically significant in affecting CO₂ capture by these pores. Scanning electron microscopy revealed “in-foldings” of pore wall in biochar samples produced under high temperature, which can help explain the relatively low correlation between CO₂ captured and pore permeability.

The global annual production of animal by-product (ABP)-derived bone, estimated at 95‒126 million tonnes, presents both an environmental challenge and an opportunity for sustainable resource utilization. We estimate that bone char (BC) could theoretically replace 13‒32% of the global phosphorus (P) fertilizer market. BC, produced through the pyrolysis of animal bones, has emerged as a promising material for use in a range of agricultural applications related to soil fertility and water quality. The conversion of ABP-derived bone into BC through pyrolysis not only eliminates potential human and animal pathogens (e.g., prions, viruses, bacteria), but also creates a valuable resource rich in P, calcium, and magnesium. This review synthesizes current research on the potential applications of BC in agriculture, focusing on its multifunctional role as a slow-release P fertilizer, a carbon (C) storage material, and an effective adsorbent for remediating contaminated soils. Field and laboratory studies demonstrate that BC’s performance is strongly influenced by pyrolysis conditions, with optimal temperatures between 300 and 500 °C for nutrient release applications and above 600–800 °C for enhanced surface area and contaminant remediation. Its hydroxyapatite structure enables gradual P release and potential toxic element (PTE) immobilization, while its porous nature can provide new habitat niches for soil microorganisms and improve soil water retention. In comparison to most conventional inorganic fertilisers, BC can enhance soil fertility by releasing P slowly, thereby improving plant growth and productivity, particularly in acidic soils. The low cost, renewable nature, and ease of regeneration of BC further enhance its appeal as a viable solution for mitigating environmental pollution and promoting sustainable resource management practices. Beyond its established applications, this review identifies critical knowledge gaps, including the need to investigate BC’s long-term impacts on soil health, microbial communities, and greenhouse gas emissions. We also discuss opportunities for optimizing production methods and expanding applications beyond agriculture. Given BC’s potential to address multiple agricultural and environmental challenges, we emphasize the importance of interdisciplinary research to evaluate implementation barriers, including economic viability, social acceptance, and regulatory frameworks.

The increasing generation of solid waste is recognized as one of the leading environmental and economic challenges. Optimal waste management, particularly in the agricultural and industrial sectors, necessitates innovative approaches for the efficient management of vital resources, including soil and water. One practical solution is the production of morpho-genetic porous carbon (MGPC) as a type of activated biochar, which has wide applications due to its porous structure, chemical and thermal stability, and high specific surface area. In this study, biochar was prepared with eight types of waste, including rice straw, vineyard prunings, palm prunings, sawdust, vinasse, poultry slaughterhouse waste, paper mill waste, and tissue paper production waste. Biochar production was carried out through a pyrolysis process under low-oxygen conditions and at a temperature of 400 °C. Biochar was converted into MGPC at a temperature of 800 °C using KOH and H₃PO₄ as activators at three different levels and CO₂ at a single level. Then, using data obtained from the Brunauer–Emmet–Teller (BET) test, the game theory approach, and the Condorcet algorithm for evaluation, 64 MGPC samples were analyzed. BET analysis was performed to measure the specific surface area and pore structure. The data obtained from this analysis were extensively reported, encompassing approximately 40 criteria. However, only 12 criteria were selected, while about 28 criteria were excluded from the Condorcet algorithm due to the incompleteness of some of their data. This study investigated the process of biochar and MGPC production using agricultural and industrial wastes, with an emphasis on the role of game theory in promoting environmentally sound decision-making and optimizing MGPC applications. From 64 prepared samples, by examining their physical properties and environmental impacts, five priority samples, i.e., rice straw-KOH-level 2, sawdust-KOH-level 2, palm tree pruning waste-KOH-level 2, vineyard pruning waste-KOH-level 2, and tissue factory waste-KOH-level 2, with respective surface areas of 1071.47, 672.04, 860.54, 667.49, and 133.45 m² g⁻¹ and t-plot micropore volumes of 0.29, 0.24, 0.17, 0.19, and 0.02 cm³ g⁻¹. were prioritized using the Condorcet algorithm. They were identified as suitable candidates for advanced applications in soil and water conservation due to their favorable porous structures and highly performed BET properties. The present study shows that innovative methods for producing MGPC can improve the performance and properties of porous materials for various applications.

This study successfully synthesized a BC/TiO₂/g-C₃N₄ composite photocatalyst using the sol–gel method, conducted an in-depth analysis of the influence mechanism of BC on charge transfer performance in heterojunction materials, and revealed its key role in regulating the charge transport process. The introduction of biochar significantly increased the specific surface area of BC/TiO₂/g-C₃N₄ compared to the TiO₂/g-C₃N₄ catalyst, broadening the visible light absorption range. Under simulated sunlight irradiation with a wavelength greater than 420 nm, the three-component material MBC-500, calcined at 500 °C, exhibits the best catalytic performance, with an adsorption photocatalytic degradation rate of 98.13% for sulfadiazine (SDZ) within 60 min, which is 3.46, 3.40, and 2.36 times that of TiO₂, g-C₃N₄, and TiO₂/g-C₃N₄, respectively. Characterization analysis and density functional theory (DFT) calculations revealed the energy band structure and electron transfer pathways of the composite photocatalyst, indicating the significant role of biochar in electron transfer and storage. Additionally, the calculated adsorption energies demonstrated the good adsorption performance of MBC-500 for O₂ and sulfadiazine. This composite photocatalyst exhibited good stability and reusability even after five cycles of use. During the degradation process of SDZ, ·O₂⁻, h⁺, ·OH play a major role.

Silicon-rich biochars (Si-chars) have demonstrated effectiveness in heavy metal remediation. However, the evolution of their functionality during environmental aging remains poorly understood. Here, we investigated the effects of artificial aging on rice husk-derived Si-chars pyrolysis at 300 ℃, 500 ℃, and 700 ℃, further evaluating their efficacy in mitigating cadmium (Cd) toxicity in soil-pakchoi systems. Aging induced a temperature-dependent response, which reduced the performance of high-temperature Si-chars but acted as an activation process for low-temperature variants. Notably, aged 300 ℃ Si-char exhibited the strongest suppression of Cd accumulation in pakchoi leaves, reducing concentrations by 27.1% and 15.6% compared to the control and non-aged 300 ℃ Si-char, respectively. This effect was attributed to the aging-induced release of bioavailable Si (ASi) and high-molecular-weight dissolved organic matter (DOM), both of which could interact with Cd to reduce its bioavailability in the amended soils. Meanwhile, ASi and DOM promoted the activities and enrichment of Cd-immobilizing bacteria. Furthermore, Si-char amendment enhanced Si deposition in pakchoi leaves, triggering a molecular defense network characterized by the down-regulation of Cd transporter genes and the up-regulation of stress-responsive pathways. Our findings establish a novel framework in which feedstock Si concentration and initial pyrolysis temperature jointly drive the functional evolution of biochar in the environment.

Biochar hydrophobicity is crucial for understanding its interaction with environmental substances (e.g., soil, water, pollutants). Contact angle (CA) and water droplet penetration time (WDPT) are commonly used methods for assessing biochar hydrophobicity. However, occasional inconsistencies between CA and WDPT measurements introduce uncertainties, emphasizing the need for more accurate evaluation. This study addressed these temporal inconsistencies by proposing a new method using the dynamic contact angle (DCA) to evaluate the hydrophobicity of 17 standard materials and 18 types of biochars. The DCA method, which considers droplet diffusion recorded CA changes over 90 s and compared the significance (p<0.05) between initial CA (CA_0) and CA after 90 s (CA_90). Based on this, a new classification of hydrophobicity was established, encompassing super-hydrophobic, strongly hydrophobic, ‘pseudo'-hydrophobic and hydrophilic categories. ‘Pseudo'-hydrophobic materials exhibited a significant decrease in CA within 90 s, where the CA transitioned from hydrophobic (CA>90°) to hydrophilic (CA<90°) within this period, revealing their hydrophilic nature. The combination of CA_0 and the rate of CA change over time (|k|) was considered as a new criterion for hydrophobicity evaluation. Through a 90-day incubation experiment of biochar and soil, most biochars significantly increased the water repellency of the biochar-amended soil, as evidenced by increases in both CA_0 and CA_90. Our DCA method, along with the definition ‘pseudo'-hydrophobicity, resolves contradictions between CA and WDPT measurements for both soil and biochar, enhancing the accuracy of hydrophobicity assessments.

Carrier-assisted delivery is a key step for the successful targeted oral delivery of bioactive molecules in functional diets in livestock. The aim is to protect the biomolecule during gastric transit, and ensure its efficient release in the intestine. Biochar is the by-product of the thermochemical conversion of residual biomass in an oxygen-limited environment and has suitable physico-chemical and morphological properties to be a carrier. Two types of biochar were tested as carriers of egg white lysozyme (LY), selected as a representative of bioactive molecules both in terms of molecular size (MW 14.3 kDa) and antibacterial activity, for application in weaned pig feed. One biochar was derived from chestnut shells (CB) and the other from vine pruning (VB). An efficient and environmentally-friendly procedure for LY adsorption was developed, based on a solid/liquid process in mild conditions. The effects of the operating conditions, such as initial LY content, reaction time, and pH were also studied. The optimal conditions were found to be a maximum LY loading of 21–23 mg_LY g_Carrier⁻¹. Both pristine and hybrid materials were extensively characterized by combining morphological and physico-chemical techniques to obtain information on LY allocation and interactions with the carriers. Preliminary experiments on lysozyme release were performed at pH=3 and pH=7, simulating the pH conditions of the stomach and intestine of the weaned pigs, respectively. The results showed a higher releasing capacity when the pH was increased from 3 to 7. Specifically, the release showed a slight increase from 0.8% to 1.2% as the pH shifted from 3 to 7 for CB, and from 1.5% to 2.3% for VB. These results confirmed that biochar can protect LY from the low pH, during the gastric transit, and that LY could be released in the gut. These two benefits are likely related to the homogeneous distribution of LY molecules at the carrier surface, which is facilitated by the interaction of charges of opposite signs.

Acidic soils are global hotspots of nitrous oxide (N₂O) emissions, and biochar has been proposed as a promising mitigation strategy. However, most current evidence comes from short-term studies, and the legacy effects and underlying mechanisms remain poorly understood. Here, we collected acidic soil samples from three sites with and without biochar application, representing short-term (3 and 5 years) and long-term (9 years) legacy effects. Using microcosm incubations, isotope-based source partitioning, and microbial analyses, we evaluated N₂O dynamics and their microbial drivers. The short-term legacy effects of biochar significantly reduced N₂O emissions by inhibiting gross N₂O production and enhancing N₂O reduction. This was primarily attributed to reduced nitrification-derived N₂O, increased nosZ gene abundance, and enrichment of taxa carrying the nosZ gene, such as Rhodanobacter and Gemmatimonas. In contrast, long-term legacy effects markedly increased N₂O emissions because biochar suppressed N₂O reduction more strongly than its production. This was linked to reduced nosZ abundance, increased fungal denitrification, and depletion of dissolved organic carbon and denitrifying bacteria. Together, these findings reveal that the legacy effects of biochar on N₂O emissions diverge over time, driven by changes in microbial nitrogen cycling pathways. These results underscore the importance of incorporating temporal and microbial perspectives when evaluating the long-term climate impacts of biochar and developing sustainable soil management strategies.

The sustained application of straw-derived biochar (BC) demonstrates considerable potential for enhancing soil organic carbon (SOC) sequestration in agricultural systems, though its efficacy is strongly influenced by soil properties, climate, and other environmental factors. We conducted an 11-year outdoor column experiment involving BC application (11.3 t ha⁻¹) under strictly controlled climatic and water–fertilizer conditions to examine the effects of successive seasonal BC application on SOC sequestration across three soil parent materials (Quaternary red clay, Tertiary red sandstone, and Yellow River alluvium) and two land-use types (paddy and upland) in China. Results showed that the joint effect of land use and parent material determines SOC sequestration efficiency of BC. Paddy soils exhibited significantly greater SOC storage, 66–323% higher than that in upland soils under identical parent material conditions. In paddy soils, recalcitrant carbon contributed a larger proportion to SOC changes than in upland soils following long-term BC application. Land use modulated microbial responses to BC: paddy soils showed higher ratios of Gram-positive to Gram-negative bacteria (G⁺/G⁻) and lower fungal-to-bacterial ratios (F/B), whereas upland soils displayed the opposite trend, particularly under Quaternary red clay and Tertiary red sandstone. G⁺/G⁻ and F/B ratios correlated positively with O-alkyl and alkyl carbon and negatively with aromatic carbon, underscoring their critical role in shaping SOC composition. Soil parent material markedly influenced microbial necromass carbon accumulation under BC amendment. Specifically, Quaternary red clay and Yellow River alluvium enhanced microbial necromass accumulation, particularly fungal-derived carbon, indicating that acidic clay loam and slightly alkaline silt loam soils are more conducive to long-term SOC stabilization. This study provides valuable insights for optimizing site-specific BC application strategies to enhance SOC sequestration.

Sewage sludge biochar (SSBC) emerges as a promising microbial inoculant (MI) carrier due to its rich organic carbon, bioavailable nitrogen species, and essential inorganic minerals. However, optimizing SSBC for MI loading and understanding its plant growth-promoting mechanisms remain challenging. Here, we developed a novel SSBC carrier, SSBC37, using a stepwise pyrolysis method: extracting dissolved matter (DM300) from the SSBC produced at 300 ℃, re-pyrolyzing the residual solid at 700 ℃, and reincorporating DM300 to preserve nutrients and create a microbial-friendly structure. DM300 enhanced the growth of Bacillus velezensis ZJ-11 by upregulating metabolic pathway genes, specifically those encoding ABC transporters. The metabolite trans-4-hydroxyproline (T-4-Hyp) produced by ZJ-11 may be involved in upregulating ABC transporter genes, thereby facilitating the uptake of DM300. SSBC37 loaded with ZJ-11 (BCZJ) significantly enhanced cabbage growth (P<0.05), increasing aboveground dry weight by 38.9±1.9% and 17.5±1.6% compared to ZJ-11 or SSBC37 alone. The loaded Bacillus increased nitrogen-related bacterial taxa Burkholderiales, through the suppression of unclassified Sordariales fungi. Furthermore, structural equation modeling (SEM) revealed that BCZJ enriched key bacterial taxa (Ramlibacter) that enhanced soil urease activity and ammonium nitrogen accumulation, thereby promoting plant nitrogen uptake and growth. This study provides a novel approach for engineering SSBC carriers to enhance MI efficacy, offering promising prospects for developing functional biofertilizer to regulate the rhizosphere microbiome for sustainable agricultural practices. Conceptual diagram illustrating the mechanism by which the growth-promoting effects of bacillus-functionalized sewage sludge biochar on cabbage. The SSBC37 prepared by stepwise method promoted the biomass and colonization of Bacillus. Bacillus-loaded SSBC37 enhance the absolute abundance of Burkholderiales by antagonizing Sordariales fungi. Finally, Bacillus and Burkholderiales collectively promote plant uptake of nitrogen.

Biochar is a promising soil amendment for controlling plant diseases, but the influence of its particle size on disease suppression remains unclear. This study focused on the differential mechanisms of fine and coarse biochars in controlling pepper Phytophthora blight, linking biochar-released compounds (BRCs) to soil microbial disease suppression. The pot experiment revealed that fine biochar provided a stronger initial suppression of disease severity and pathogen abundance, but these effects diminished over time, whereas coarse biochar provided a more durable control effect. Similar time-dependent effects were observed for the increase in total and biocontrol microbial abundances. The mesh-bag experiment confirmed that fine biochar rapidly released minerals and labile organic carbon (LOC) in the early stage. This initial release significantly increased the abundances of total bacteria, total fungi, Pseudomonas, Trichoderma, and Penicillium, as well as the antagonist percentages of total bacteria and fungi, while suppressing Phytophthora capsici. However, the reduced release of BRCs in the later stage markedly weakened these effects. In contrast, coarse biochar provided more durable suppression through a slower, more sustained release of BRCs, resulting in a greater improvement in microbial properties during the later stage. Mantel tests and PLS-PM analysis indicated that electrical conductivity (representing minerals) and LOC were the key drivers that enhanced microbial abundance and antagonism, which in turn effectively suppressed the pathogen. This study reveals that biochar particle size influences the release rate of BRCs, resulting in a time-dependent control effect. These findings provide new insights into developing precise and sustainable disease control strategies.

This work investigates the impact of micro-nanoscale bone char (MNBC) soil amendment on Cd-stressed rice over a full life cycle, aiming to develop a sustainable remediation strategy integrating yield improvement and soil health. MNBC was sourced from widely available pork bones in the waste stream, and was generated by pyrolysis at 400 °C and 600 °C, followed by ball-milling to reduce the particle size to micro-nanoscale. A 140-day full-life-cycle experiments was conducted under greenhouse conditions, and soil samples across all the treatments were collected at different growth periods for metagenomic analysis. At harvest, rice grains were sampled for metabolomic analysis. Results showed that treatment with 600 °C MNBC significantly increased grain yield by 49.72%, while 400 °C MNBC increased the effective tiller number by 23.08%, compared to Cd treatment. Both types of MNBCs reduced Cd accumulation in rice tissues, with reductions of 65.0–68.7% in polished rice relative to the Cd treatment. Metabolomic analysis highlights MNBC modulated the nutritional value of the grains, effectively slowing down the biochemical processes of carbohydrates and branched-chain amino acids into simple sugars or polyols in rice grains. In the aerobic phase of soil, the acid-soluble Cd with MNBC treatments decreased by 31.56–35.51% as compared to the Cd treatment. Metagenomic analyses show that MNBC had a significant impact on the microbial communities involved in soil carbon, nitrogen, and phosphorus cycling, such as Actinomycetota, Cyanobacteria, and Gemmatimonadota, as well as on related genes; particularly enhancing the complexity of the phosphorus gene network. Overall, these findings demonstrate the significant potential of MNBC-enabled agriculture practices as a sustainable crop strategy.

The recalcitrant antibiotics of enrofloxacin (ENT) and amoxicillin (AMT) were difficult to remove by conventional sonication. To address this challenge, a new type of carbon nanotube covalently bonded biochar@Fe₃C composite (BCM@Fe) was first designed by calcination and employed as a solid cavitation material (SCM) under low-frequency ultrasound (US) conditions to accelerate the removals of ENT and AMT. Compared to conventional carbon nanotube@Fe₃C composites, BCM@Fe demonstrated significantly improved removal performance, achieving 15.5-fold and 3.50-fold higher removal rates for ENT and AMT, respectively. The removal efficiencies increased by 32.1–32.3% compared with a conventional shake system. Mechanistic studies revealed a dual removal mechanism involving simultaneous adsorption and degradation. The coupling of low-frequency ultrasound with BCM@Fe had synergistic effects; the US promoted the dispersion of the composites and inhibited H₂O-induced oxidation by generating surface-localized cavitation bubbles. Notably, BC in BCM@Fe was found to amplify cavitation effect with performance strongly correlated with material characteristics such as pH, carbonization degree, aromaticity, hydrophobicity, and graphitization. Degradation differed between antibiotics: the degradation of ENT predominantly occurred at the material surface, while that of AMT took place in the liquid phase. Overall, the successful access to low-cost SCM integrating with low-frequency ultrasound made the possible for potential application in antibiotic wastewater.

Organic phosphorus can cause environmental pollution easily through leaching in natural systems. Here, calcium-modified biochar was prepared to adsorb inositol hexaphosphate (IHP), glycerophosphoric acid (GP), D-glucose 6-phosphate (G6P), and adenine nucleoside triphosphate (ATP), and the impacts of their molecular structures were explored via batch experiments, characterizations, and theoretical calculations. The adsorption of ATP occurred mainly through hydrogen bonding and electrostatic interactions, while that of the others took place through chemical precipitation, where calcium-based active sites functioned and maintained the adsorption stability in different environments. Further, the time-of-flight secondary ion mass spectrometry confirmed the roles of P groups and carbon chains through P-related and CN⁻ signals. With more reactive P groups (P1,3 and P4,6) and lower molecular electrostatic potentials, IHP achieved significantly higher adsorption (292.1 mg P g⁻¹) although its adsorption energy for a single P group was not optimized. As for GP, G6P, and ATP, the surface occupation by carbon chains became visually prominent. The desorption results showed that released OPs ranged from 20% to 80%, and the adsorption via multiple P groups reduced the desorption of IHP and ATP under different conditions. These results highlight the importance of biochar for OPs’ utilization, emphasize the necessity of multi-method sets, and elucidate the molecular mechanisms of interactions.

Efficient biomass biochar-supported metal catalysts are essential for the conversion of biomass-derived chemicals. However, there is a lack of in-depth research on the function of biochar support. This research describes the direct loading of untreated sunflower stem pith (SP) with metal–organic frameworks (MOFs) as precursors, which were carbonized in a single step to produce Co-atom-evenly-doped biomass biochar support (Co/SPC), subsequently loaded with a low concentration of Pd to create a bimetallic catalyst (Pd-Co/SPC). The catalyst demonstrated remarkable efficacy in the hydrogenation of furfural (FAL) to tetrahydrofurfuryl alcohol (THFA), achieving a 99.9% yield within 1 h at 100 °C. This performance significantly surpassed that of Pd/SPC (28.1%) and the inactive Co/SPC, with the 99.9% yield sustained even at the milder temperature of 40 °C. The excellent catalytic performance of the Pd-Co/SPC catalyst was attributed to three main aspects. First, controlled experiments and characterization results demonstrated that the acidic and basic nature of the sunflower pith-derived biochar support promoted the activation of FAL. Second, the interaction between the biochar support and the metal not only inhibited the agglomeration of metal particles but also augmented the electron density of the PdCo metal and facilitated the activation of H₂. Finally, the synergistic interaction between the highly dispersed Pd and Co facilitated the activation of H₂ and stabilized the intermediate furfuryl alcohol (FOL). Furthermore, this superior metal-support interaction contributed to the increased stability of the catalyst. This work presents a novel approach for the high-value utilization of biochar and highly efficient catalysis of biomass conversion.

Straw and biochar amendments markedly influence soil N₂O emissions in subtropical Moso bamboo forests, but the microbial mechanisms driving these responses remain elusive. This study aimed to assess the contrasting influences of maize straw and its derived biochar on soil N₂O emissions in a subtropical Moso bamboo forest. Straw amendment (5 t C ha⁻¹) stimulated N₂O emission by 16–27% (P<0.05). However, biochar addition (5 t C ha⁻¹) decreased the concentrations of NH₄⁺ by 11–14%, NO₃⁻ by 11–15% and water-soluble organic nitrogen for 14–17%, and decreased the abundances of ammonia-oxidising bacterial amoA by 40–45%, nirK by 30–36%, nirS by 24–32% and associated genera Nitrosospira, Mesorhizobium, Bradyrhizobium, Rhizobium, Pseudomonas, and Cupriavidus. Biochar also decreased the activities of enzymes related to organic N hydrolysis (protease and urease) and denitrification (nitrate reductase and nitrite reductase), and thus decreased N₂O emissions by 17–20% (P<0.05). Furthermore, biochar enhanced the abundance of nosZ gene (by 40–46%) and its dominant genera (Mesorhizobium, Bradyrhizobium, and Azospirillum), which facilitated N₂O reduction. In contrast, straw inhibited the growth of these dominant genera and lowered the abundance of nosZ gene (by 24–38%). These results highlight the varied responses of nitrification and denitrification processes and hence N₂O emission to the application of straw and biochar in soils of a subtropical Moso bamboo forest.

Heavy metal contamination in global agricultural soils has posed severe ecological and health risks. However, little is known about the long-term effects of soil management on the bioavailable concentration and the speciation of heavy metals, especially via physicochemical and microbial processes. Utilizing a 14-year field trial, we showed that high-dosage biochar (HBC) effectively reduced heavy metal bioavailability by 2–91%, outperforming low-dosage biochar (LBC) and straw amendments. Both HBC and LBC drove residual Cd, Zn, and Pb toward reducible fractions, whereas straw exhibited no significant impact. Partial least squares-structural equation modeling and variance partitioning analysis indicated that the concentration and speciation of metals were co-regulated by physicochemical and microbial properties, with microbial attributes dominating bioavailability (30% variance) and physicochemical governing speciation (12%). Specifically, biochar reduced bioavailability by increasing the cation exchange capacity (CEC), soil organic carbon (SOC), and free iron oxides, coupled with enriching Entomophthoromycota and Nitrospirae while suppressing Bacteroidetes and Verrucomicrobia. Conversely, straw increased bioavailability by decreasing CEC but enhancing enzyme activity alongside Bacteroidetes or Verrucomicrobia. For metal speciation, biochar drove the transformation of speciation by enhancing SOC, aromatic compound levels, and Zoopagomycota, but suppressing Ascomycota and Latescibacteria. By evaluating the coupling index of heavy metal immobilization and carbon sequestration, we showed that HBC had a higher score (0.703) than LBC (0.361) and straw (0.396). This indicated that HBC can more effectively immobilize heavy metals than LBC and straw, and achieve extra benefits in promoting carbon sequestration. Our results provided insights into adjusting soil management practices to achieve soil multi ecosystem functions and improve agricultural sustainability.

Red mud, a saline-alkaline and metal-contaminated byproduct, poses severe ecological risks. This study elucidates the synergistic remediation mechanisms of biochar (BC) combined with arbuscular mycorrhizal fungi (AMF) in an Arundo donax-soil system. We specifically investigated biochar loaded with Funneliformis mosseae (BC–FM) and that loaded with Rhizophagus intraradices (BC–RI). The BC–FM treatment significantly enhanced the plant antioxidant system and photosynthetic capacity while reducing the content of exchangeable arsenic (As) and soil pH, thereby inducing a “photosynthesis enhancement-As immobilization” synergy. In contrast, the BC–RI treatment markedly increased plant biomass and soil microbial α–diversity, while simultaneously reducing the contents of soil lead (Pb) and sodium ions (Na⁺) and enhancing alkaline phosphatase activity—thus demonstrating a “Pb fixation–microbial diversity–soil phosphorus (P) activation” cascade. Rhizosphere network analysis identified key bacterial genera, with Longimicrobiaceae driving soil organic carbon accumulation in the BC–FM treatment and Lechevalieria enhancing alkaline phosphatase (ALP) activity in the BC–RI treatment. These findings support a novel “fungal species–heavy metal valency matching” principle, where RI preferentially targets cationic Pb, while FM targets anionic As. This principle establishes a three-dimensional synergistic model: “Heavy metal transformation–concurrent salinity-alkalinity mitigation–microbial function activation”. The results provide a foundational strategy for zonal red mud remediation: applying BC–RI in Pb–dominated areas and BC–FM in As–contaminated areas.

Engineered biochar materials are under development for a wide range of environmental applications. Many of these engineered materials combine biochar with minerals such as non-clay silicates, clay minerals, oxide minerals, and carbonates, or are manufactured through the co-pyrolysis of mineral additives with the biomass, both forming organo-mineral complexes. In this review, we provide an exploration of the mechanisms of organo-mineral interactions, physicochemical changes, and real-world practical applications. We first provide an overview of organo-mineral interactions between biochar and minerals in the natural environment to offer insights into organo-mineral interactions in engineered biochar composites. Secondly, we propose a classification of biochar composites with minerals. A quantitative analysis of physicochemical changes in engineered biochar composites is presented, revealing an increase in ash content and polarity, with either improved or degraded porous structure. Based on these physicochemical changes, enhancement mechanisms of the mineral components are assessed. These mechanisms primarily involve direct stabilization of biochar carbon (C) and indirect negative priming when applied to soil, nutrient delivery, introduction of functional groups for adsorption/immobilization, and reduced toxicity to support microbial colonization and improve soil health. In addition, evidence for the practical application of biochar-mineral composites is presented, including field studies for soil applications and pilot-scale non-soil applications such as in wastewater and stormwater treatment. Finally, challenges and future research directions are proposed, including examining the molecular binding mechanisms between minerals and the C matrix, investigating the reversibility of mineral attachment and the long-term effectiveness of composites, and exploring emerging non-soil applications of novel biochar composites with minerals.

The low fertilizer utilization efficiency and metal(loid) contamination have become dual challenges that constrain the production of rice and thus food security. To address these issues, a life-cycle greenhouse study was conducted with rice (Oryza sativa) grown in soil co-contaminated with cadmium (Cd) and arsenic (As) and treated with several synthetic fertilizers. These fertilizers included regular fertilizers (F), biochar-based fertilizers (BF) and nano-biochar-based fertilizers (NBF), each formulated with varying nitrogen:phosphorus:potassium (N:P:K) ratios (I, II, and III). The results revealed a differential suppression of Cd (strongest under F-I, followed by NBF-III) and As (strongest under F-II, followed by NBF-I) in rice grains, attributable to disparities in their environmental chemistry, bioavailability, and plant-mediated uptake and translocation mechanisms. While BF enhanced catalase and alkaline phosphatase activities, NBF more effectively stimulated urease activity throughout the 0–10 cm layer and sucrase activity in the deeper 5–10 cm zone. Notably, NBF increased soil metabolic diversity under Cd and As stress while strengthening the genetic regulatory capacity and environmental adaptability of microbial communities. Furthermore, NBF dynamically regulated the migration of Cd and As into porewater, resulting in more stable and effective immobilization compared to BF and F treatments. These findings highlight that the application of biochar, particularly nano-biochar, for paddy soil remediation necessitates a contaminant-specific and nutrient-managed strategy. Tailoring both the biochar type and the accompanying N:P:K ratio is crucial for targeting the biogeochemical behavior of the dominant contaminant, thereby ensuring grain safety and supporting sustainable rice production.

Acid-hydrolysable nitrogen (AHN), a crucial fraction of bioavailable soil organic nitrogen (N), is highly sensitive to soil acidification. Alkaline biochar (BC) has been shown to effectively mitigate acid rain (AR)-induced soil acidification. However, its regulatory effects and underlying mechanisms on AHN fractions remain largely unexplored. In this study, a field-scale simulated AR experiment was conducted in a Quercus acutissima plantation, utilizing BC derived from Q. acutissima litter to evaluate its impacts on AHN fractions and associated soil chemical-biological drivers. The results showed that after 2 years of simulated AR spraying, BC application elevated soil pH by 0.19 units under AR stress and increased total AHN content by 64.8%. Specifically, acid-ammonia N, acid-amino sugar N, acid-amino acid N, and acid-hydrolyzable unidentified N increased by 45.0%, 61.3%, 80.6%, and 60.7%, respectively. BC-amended soils under AR exhibited the highest bacterial network complexity (0.8), whereas fungal network connectivity was reduced. Soil chemo-biological interactions explained 23.1−39.7% of the variations in AHN fractions. Random forest modeling identified microbial N use efficiency as the primary factor influencing acid-ammonia N, and microbial biomass N as the key factor governing the accumulation of acid-amino acid N and acid-amino sugar N. Furthermore, the regulatory effects of BC on AHN fractions (0.77–0.98) surpassed those of AR stress. This study elucidates the mechanistic pathways through which BC modulates acid-induced N dynamics, providing insights for sustainable N management in plantation ecosystems affected by AR.

The aging mechanisms of modified biochar for arsenic (As) immobilization at micro/nano-interfacial scales in diverse soils remain poorly understood. Herein, we employed three aging treatments, including natural aging (NA), freeze–thaw cycles (FT), and dry–wet alternation (DW), to simulate the aging behavior of cerium-manganese modified biochar (CMBC) in two As-contaminated field soils. Results indicated that CMBC amendment significantly reduced soil pH by 7.5–16.7%, while simultaneously increasing dissolved organic carbon contents by 10–45%, available phosphorus levels by 11–43%, and the activities of four soil enzymes by 30–320% in comparison to unamended soils. These improvements proved to be most effective under FT-aging, followed by DW-aging and NA-aging. FT-aging also led to the most pronounced reduction in water-soluble As concentrations ranging from 94 to 99%, as well as a decrease in As mobilization coefficients of 38% to 59% in CMBC-amended soils when compared to DW-aging and NA-aging. The superior As immobilization under FT-aging can be attributed to adhesion mediated by Ce–Si crystal nano-bridge between soil microparticles and CMBC matrix, whereas such adhesion was not observed in NA/DW-aged samples. This unique interfacial configuration promoted Ca/Fe-oxide intercalation and amorphous Ce-oxides formation within CMBC, which facilitated the development of As–Fe/Ce crystalline phases. Meanwhile, the synergistic enrichment of metallic and oxygen-containing groups on FT-aged CMBC surface induced the formation of stable As–Ce/Fe–O species and triggered dual redox transformations: (1) Ce/Mn reduction drove bulk As(III) oxidation to As(V), and (2) Fe(0) oxidation mediated partial reduction of As(V)/As(III) to inert As(0). Notably, CMBC-amended red soil exhibited preferential As immobilization during aging due to the tighter adhesion between nano-CMBC and soil colloids. This enhanced adhesion strengthened the bonding of Ce/Fe-oxides with As and intensified the oxidation of As(III) to As(V) through increased Ce/Mn reduction. This study provides innovative microscale mechanistic insights into the aging behavior of modified biochar for remediating diverse soils contaminated with potentially toxic elements.

The application of biochar to agricultural soils is a promising strategy for reducing greenhouse gas emissions and enhancing carbon sequestration. However, the microbially mediated mechanisms by which biochar influences soil carbon cycling remain unclear. Through a meta-analysis, we evaluated the responses of soil organic carbon (SOC) and microbial communities to biochar application, aiming to elucidate microbial regulatory roles in biochar-induced carbon sequestration processes. Our results demonstrated that biochar significantly increased all SOC fractions (mean increase: 52.4%), along with concurrent increases in soil total nitrogen (17.6%) and pH (4.1%). Divergent ecological strategies among bacterial phyla drove different SOC responses. When broad-niche phyla functioned as the sensitive (Proteobacteria) or dominant (Actinobacteria) taxa under our sensitivity classification, they facilitated the greatest SOC increases (68.6% and 52.4%, respectively), exceeding the overall mean. Oligotrophic phyla (Acidobacteria and Chloroflexi) domination resulted in limited SOC gains (47.3% and 28.8%, respectively). Broad-niche phyla exhibited enhanced organic carbon decomposition and nutrient utilization, promoting SOC accumulation. In contrast, oligotrophic phyla, typically adapted to low-nutrient environments, demonstrated suboptimal carbon utilization, possibly even accelerating SOC decomposition, ultimately reducing the net carbon sequestration. Overall, we revealed the microbial regulatory mechanisms governing biochar-induced carbon sequestration, providing a basis for evaluating biochar carbon sequestration based on microbial communities.

To address the high environmental sensitivity of oxygen release from calcium peroxide (CaO₂) in practical applications, this study proposes and validates a synergistic regulatory strategy combining chemical anchoring and physical confinement. Three modified rice husk biochars were prepared via nitric acid oxidation, KOH activation, and phosphate loading, followed by CaO₂ loading. The biochar prepared via KOH activation (B_Si-) possessed an ultra-high specific surface area (2629.49 m² g⁻¹). Consequently, the CaO₂@B_Si- composite exhibited high loading capacity (15.74%) and rapid oxygen release. In contrast, nitric acid oxidation resulted in a biochar carrier (B_N) with a damaged pore structure and a strongly acidic surface, which led to the lowest CaO₂ loading (1.31%). The phosphate-modified biochar (B_P) enabled CaO₂@B_P to achieve both high loading capacity (10.49%) and sustained slow oxygen release, which was attributed to the formation of stable Ca−P bonds. The CaO₂@B_P exhibited superior environmental robustness, being largely independent of pH, ionic strength, and initial dissolved oxygen concentration. Partial least squares regression modeling quantitatively revealed that both phosphorus content and mesopore volume were core factors determining the loading capacity, whereas both H/C ratio and surface functional groups regulated the oxygen release kinetics. The phosphate modification may be an optimal strategy for preparing environmentally adaptive oxygen-releasing materials with both high loading and good stability.

Arid and semi-arid regions are increasingly vulnerable to desertification, soil degradation, and water scarcity, which severely threaten agricultural productivity, food security, and ecosystem stability. This review explores biochar as a climate-smart, integrative, nature-based solution to address these critical challenges, enhance water use efficiency, and build resilience in fragile dryland ecosystems. We hypothesize that strategically designed biochar systems aligned with consistent feedstock logistics, economic viability, and site-specific hydrological and biogeochemical needs can serve as scalable, multi-functional interventions to restore degraded soils and mitigate climate-driven desertification. To test this hypothesis, we critically synthesize interdisciplinary literature, uncovering underexplored synergistic roles of biochar in hydrological regulation, microbial ecology, and renewable energy integration. By consolidating data on biochar’s physicochemical properties, we examine its mechanisms for improving soil structure, boosting water retention, enhancing nutrient cycling, buffering pH, and supporting microbial communities in dryland soils. Field evidence further demonstrates biochar’s capacity to rehabilitate soils, increase crop yields, and reduce erosion risks. We also highlight emerging opportunities at the intersection of biochar and precision agriculture, such as drone-assisted applications, co-composting to produce nutrient-rich biochar, and integration with solar-powered irrigation. Given the accelerating trends of land degradation and climate variability, there is an urgent need to optimize biochar systems for specific soil–climate contexts, quantify long-term carbon sequestration, and assess ecosystem-level impacts. Overcoming challenges related to high production costs, feedstock variability, and ecological uncertainties will require coordinated, multidisciplinary efforts. In conclusion, this review emphasizes biochar’s multifaceted role as a transformative strategy for climate-resilient agriculture and sustainable land management in drylands.

The application of organic materials has a profound impact on CH₄ emissions from paddy fields. Biochar has been reported to mitigate CH₄ emissions, but this conclusion has recently been challenged and requires further investigation. This study aimed to determine the effect of biochar on paddy CH₄ emissions by integrating organic amendment emission data through network meta-analysis (NMA), and to identify the key moderators using multiple meta-regression (MR) approaches. Field experiments were conducted to verify the conclusions of MR. Based on 146 entries from 51 studies, a mixed-effects meta-analysis was conducted to evaluate the effects of organic material applications on soil CH₄ emissions. We focused on the biochar mitigation potential in rice systems and validated the conclusions through a field experiment. Biochar demonstrated the lowest methane emissions among all treatments. Carbon to nitrogen ratio of biochar (MC:N) and mineral nitrogen input (ICN) were identified as key moderators influencing the methane mitigation potential of biochar in rice cultivation. ICN was the most influential factor. When ICN exceeded 291.18 kg ha⁻¹, biochar tended to increase methane emissions, whereas at lower ICN levels, it contributed to emission reductions. Field experiments confirmed that at high mineral N levels (310 kg ha⁻¹), biochar significantly increased CH₄ flux and emission potential. Overall, this study highlights the potential of biochar to reduce methane emissions in rice systems and underscores the importance of regulating mineral nitrogen inputs to maximize its mitigation effectiveness.

The global prevalence of emerging pollutants (EPs) in aqueous systems presents a significant environmental threat that conventional treatments cannot adequately address. This review provides a comprehensive analysis of biochar-based systems as a sustainable solution, charting a path from foundational material science to advanced, data-driven engineering. We critically evaluate these solutions through a tiered framework: starting with Tier 1 (Pristine Biochar), which is highly reliant on physisorption mechanisms; moving to Tier 2 (Modified Biochar) with enhanced surface properties through activation and/or heteroatom doping; and culminating in Tier 3 (Advanced Composites) incorporating materials like nanoparticles and graphene, which offer superior removal mechanisms, including chemisorption and photocatalysis. A central focus is placed on the transformative role of Artificial Intelligence (AI), which enables predictive modelling and optimization to accelerate the design of tailored, high-performance adsorbents. Beyond performance, this review delves into the critical aspects of scalability, presenting a detailed analysis of the economic trade-offs and environmental/ecotoxicity considerations that govern real-world deployment. We demonstrate how this tiered approach leads to targeted solutions for challenging EPs, such as cationic composites for per- and polyfluoroalkyl substances and engineered surface porosity for the physical entrapment of micro- and nanoplastics. Ultimately, we advocate for an AI-guided strategy, prioritizing sustainable pristine biochar where effective and strategically deploying advanced composites as a last resort. This work concludes by outlining a roadmap for future research, emphasizing the need for standardized and robust datasets, green synthesis protocols, and rigorous safety assessments to ensure the responsible development of these next-generation water treatment technologies.

Biochar enhances soil nutrient availability and promotes flowering. Biochar nanoparticles (BCNPs), a key biochar component, migrate into plant tissues to regulate flowering; however, the mechanisms remain unclear. We investigated the impact of biochar on Gentiana szechenyii Kanitz. (G. szechenyii) flowering under nutrient-rich conditions. Biochar (18 g) application increased flower number by 24.2%, with no significant changes in soil N, P, K, Mg, S, Si, Zn, and Mn. Transmission electron microscopy showed increased BCNPs accumulation in chloroplasts and higher starch concentration in leaves, while sucrose levels remained unchanged. ¹³CO₂ isotope tracing revealed reduced ¹³C in leaves and flower branches. Transcriptomic analysis revealed the upregulation of genes involved in sucrose-starch metabolism, flowering regulation, floral meristem development, and hormone. The study shows that BCNPs, after detaching from biochar, migrate into plant tissues and regulate carbon allocation, as well as the expression of flowering- and hormone-related genes, synergistically promoting flowering. BCNPs enhance source activity and sink capacity, with a preferential increase in sink strength, thereby increasing flower number. This study advances the understanding of biochar nanomaterial applications in agriculture.

Soil microorganisms are central to nutrient cycling and soil fertility, and their dynamics are strongly influenced by agricultural management practices. Peanut shell biochar has been widely applied to enhance soil fertility and reduce nutrient loss. However, its long-term effects on soil microbial communities under large-scale field conditions remain poorly understood. To address this knowledge gap, we conducted multi-year field experiments across five major tobacco-growing regions in China. Compared with the control group, long-term addition of peanut shell biochar significantly improved various soil chemical properties in Mudanjiang, Shangluo, Yichun, and Yanshan Town, including pH, available potassium, available phosphorus, organic matter, carbon-to-nitrogen ratio, alkaline hydrolyzable nitrogen, sucrase activity, catalase activity, and urease activity, while reducing the available phosphorus and catalase activity in Xuchang. Soil microbial diversity and community composition exhibited significant variation across sites, primarily shaped by differences in soil chemical properties. Although overall microbial diversity was not significantly altered by biochar addition, specific taxa, such as Firmicutes, Zoopagomycota, and Blastocladiomycota, were enriched, with Bacilli representing 70% of the significantly enriched bacterial taxa. Co-occurrence network analysis revealed that biochar amendment enhanced the complexity and stability of bacterial networks but reduced those of fungal networks. Furthermore, long-term biochar application enhanced soluble sugar content through pathways involving soil organic matter, bacterial community diversity, and specific enriched bacterial taxa. Collectively, these findings underscore the important role of peanut shell biochar in promoting the stability of bacterial networks and enhancing crop quality, providing a sustainable strategy for improving soil health and agricultural productivity.

Estuarine wetlands serve as essential carbon sinks; however, their sequestration capacity is increasingly threatened by anthropogenic activities and climate change. While biochar incorporation shows promise for restoration, its role and mechanism in estuarine wetlands remain poorly understood. Most research has focused on terrestrial ecosystems without considering the unique conditions of estuaries, including strong hydrodynamics and persistent sediment deposition. To bridge this gap, we conducted a 1-year in-situ experiment in the Chongming Dongtan wetland to assess the carbon sequestration potential of reed straw-derived biochar under tidal influence. Compared to the control and straw return treatment, biochar incorporation significantly suppressed sediment respiration by 49.01% and 61.53% (p < 0.05), respectively. Consequently, biochar achieved an average 31.37% increase in soil organic carbon content relative to the control, outperforming its application in comparable agricultural ecosystems. Furthermore, biochar significantly decreased the ratios of dissolved and easily oxidizable organic carbon (p < 0.05), indicating improved soil organic carbon stability. Mechanistically, tidal dynamics and sediment deposition altered the impact of biochar on sediment properties, specifically by decreasing NH₄⁺-N, maintaining bulk density, and increasing sand/clay ratio, which were identified as key factors affecting microbial activity by redundancy analysis and structural equation modeling. These shifts inhibited microbial carbon mineralization by reducing functional genes (e.g., chiA, FAEB, and pel) and associated genera (Anaeromyxobacter and Geobacter), while enriching genes and microbial taxa related to carbon stabilization, such as aspB and Anaerolinea. Thus, the carbon sequestration potential of biochar in estuarine wetlands was amplified. These findings offer valuable insights into biochar incorporation in wetland restoration and enrich our understanding of its role across diverse ecosystems, suggesting that it may yield greater carbon benefits in estuaries than in terrestrial ecosystems.

Urbanization generates vast quantities of excavated soils, yet their carbon emissions remain poorly quantified. This study presents the first field-based quantification of CO₂ and CH₄ fluxes from excavated urban soils stockpiled at a vacant site in South Korea, and evaluates the effectiveness of biochar amendment and soil capping as carbon mitigation strategies. Surface-exposed excavated soils emitted 12.78 ton C ha⁻¹ yr⁻¹ (CO₂: 12.54, CH₄: 0.24), corresponding to an annual SOC decomposition rate of 1.45%. When excavated soils amended with 2% (w/w) biochar were deeply buried (40–60 cm), annual CO₂ and CH₄ fluxes were significantly reduced by 42.5% and 95.8%, respectively. Separately, under surface-exposed conditions, biochar amendment alone reduced annual CO₂ and CH₄ fluxes by 8.9% and 25%, respectively. At the national scale, unused excavated soils are estimated to have emitted 0.14 ± 0.44 Mt C between 2019 and 2023, of which around 0.06 Mt C could have been mitigated through deep burial combined with biochar amendment. Furthermore, biochar contributes an additional 3.78 Mt C of long-term carbon sequestration, resulting in a total mitigation potential of 3.84 Mt C, equivalent to 15% of South Korea’s waste sector emissions over the same five-year period. These findings establish excavated soils as an overlooked but substantial carbon emission source and demonstrate that biochar amendment and soil capping offer scalable, nature-based solutions with relevance to urban planning and national carbon mitigation efforts.

Mobilizing legacy phosphorus (P) in greenhouse soils offers a strategy to alleviate P limitation and enhance crop productivity. This study applied biochar-Bacillus consortium as a bio-organic soil amendment. By altering the soil bacterial community, it improved P availability and plant P uptake, promoted root and inflorescence development, and ultimately increased cherry tomato yield. Specifically, soil application of biochar-Bacillus consortium (BM) significantly enhanced soil available phosphorus by 10.16%, microbial biomass phosphorus by 174.76%, and alkaline phosphatase activity by 68.52% in the rhizosphere relative to the control (CK). This enhancement in P bioavailability was significantly correlated with shifts in the soil bacterial community. Compared to treatments with biochar alone (B) or Bacillus liquid culture (M) alone, the enhanced P availability promoted plant P uptake and improved root architecture, as reflected by significant increases in root length, surface area, volume, and tip number. In addition, the improvement of inflorescence development was reflected in a substantial increase in the proportion of effective fruit branches, thereby contributing to a significant yield enhancement of 23.53%. Collectively, this work demonstrates that amending soils with a biochar-Bacillus consortium effectively enhances P bioavailability and cherry tomato productivity, thus emphasizing its potential for sustainable intensification in controlled agricultural systems.

The valorization of agricultural waste into functional materials offers a sustainable route for developing advanced water treatment technologies. In this study, microalgae biomass was converted into biochar and subsequently functionalized with amine groups via a one-step mussel-inspired polymerization and Schiff-base addition reaction. The resulting novel amine-functionalized biochar (AFBC) was incorporated into cellulose acetate (CA) membranes using the nonsolvent-induced phase separation (NIPS) method to fabricate hybrid ultrafiltration membranes. Comprehensive structural and physicochemical analyses confirmed the successful functionalization of the biochar and its uniform distribution within the CA matrix. AFBC incorporation significantly enhanced the membrane's hydrophilicity, porosity, and surface charge, leading to improved rejection of natural organic matter (NOM). The membrane containing 4 wt.% AFBC achieved a flux of 169.1 LMH and 64.1% NOM removal efficacy during municipal wastewater filtration, outperforming the pristine CA membrane (81.8 LMH, 31.1% removal). Moreover, the modified membrane demonstrated complete bacterial removal, partial elimination of other contaminants, and a high flux recovery ratio (82.7%), indicating excellent antifouling properties. These findings establish AFBC as a promising sustainable filler for the development of high-performance hybrid membranes for eco-friendly municipal wastewater treatment.

Enhancing soil organic carbon (SOC) and aggregate stability is pivotal for maintaining soil health and ensuring agricultural sustainability. However, conventional organic amendments often exhibit suboptimal efficiency in achieving these goals. Hydrochar, synthesized via hydrothermal carbonization (HTC), offers a promising solution by integrating labile and recalcitrant carbon fractions to synergistically address these challenges. However, its mechanisms of action remain not fully understood. In the present study, a microcosmic incubation experiment was conducted to evaluate the short-term impacts of hydrochar on SOC sequestration and soil aggregation in comparison with biochar and straw in a purple soil (Entisol). Hydrochars derived from maize straw (SH), pig manure (PH), and Zanthoxylum stalks (HH) were also compared to assess feedstock-driven variability. The results demonstrated the superior performance of hydrochars, particularly those derived from Zanthoxylum stalks, which significantly increased the mean weight diameter (MWD) by 70–100% and SOC content by 143–149%, outperforming biochar and straw. Specifically, hydrochar-originated carbon persisted primarily as particulate organic matter (POM) and accumulated in macro-aggregate, while shifts in microbial communities contributed to SOC stabilization. In comparison, soil aggregation was driven by labile carbon fractions (e.g., dissolved organic carbon, DOC) and soil microorganisms, specifically Actinobacteria and Ascomycota. Feedstock properties, such as the C/N ratio and lignin content, modulated the effectiveness of hydrochar as a soil amendment. Notably, stalk-derived hydrochar exhibited superior carbon retention (12% total carbon loss vs. 30–44% for other amendments) and aggregate stability due to its recalcitrant lignin structure. Nutrient content and ratio further influenced these outcomes, with manure-derived hydrochar promoting microbial biomass carbon (845 mg kg⁻¹ vs. 350 mg kg⁻¹ in control), while stalk-derived hydrochar was more effective at optimizing carbon sequestration. These findings highlighted the dual role of hydrochar in enhancing soil structure and SOC sequestration, with feedstock selection critically determining functional priorities. Such insights could provide valuable guidance for tailoring hydrochar production and application to improve agricultural sustainability through soil quality improvement.

Biochar amendment is an effective strategy for mitigating methane (CH₄) emissions in paddy fields. However, the long-term efficacy of different biochar amendment strategies for mitigating CH₄ emissions remains unclear, particularly under different water management regimes. To address this knowledge gap, a 5-year (2018–2022) field experiment was conducted to determine CH₄ production potential, CH₄ oxidation potential, and CH₄ emissions in paddy fields under six treatments: flooded irrigation (F) without biochar amendment (FB0), F with once biochar amendment (12.5 t ha⁻¹, FB1), F with continuous biochar amendment (2.5 t ha⁻¹ year⁻¹, FB5), controlled irrigation (C) without biochar amendment (CB0), C with once biochar amendment (12.5 t ha⁻¹, CB1), and C with continuous biochar amendment (2.5 t ha⁻¹ year⁻¹, CB5). Additionally, random forest analysis and structural equation modeling (SEM) were used to elucidate interaction pathways among biochar amendment, water management, CH₄ production and oxidation potentials, and key soil properties affecting CH₄ emissions. In the first year, once biochar amendment demonstrated optimal CH₄ mitigation efficacy under different water management regimes, reducing cumulative CH₄ emissions by 18.87–36.32% compared to other treatments. However, this mitigation effect diminished progressively over 5 years under different water management regimes, with the most rapid decline occurring under C. Consequently, there was no significant difference in the 5-year cumulative CH₄ emissions between FB1 and FB5, while CB5 achieved a significant 29.32% reduction in 5-year cumulative CH₄ emissions compared to CB1. Random forest analysis and SEM identified soil redox potential (Eh), dissolved organic carbon (DOC), and ammonium nitrogen (

Highlights

Biochar is widely recognized as a green and sustainable amendment for saline-alkali soils. However, the aging process can alter its properties and compromise its long-term effectiveness in improving soil quality. Despite its significance, limited information is available on biochar aging in saline soils. This study investigated the mechanisms by which soil salinization influences biochar aging and microbial colonization characteristics. Biochar samples collected from agricultural fields with different salinity levels were subjected to repeated wet–dry cycles simulating approximately 8 years of natural aging and analyzed for changes in chemical and microbial properties. The results revealed that increased soil salinization slowed the aging process of biochar. Biochar aged in high-salinity soils retained significantly higher total carbon, aromaticity, and surface C–C/C = C carbon contents than those in low-salinity soils, whereas its total oxygen content, degree of oxidation, and surface C–O content were markedly lower. In the final cycle, the O/C ratio of biochar aged in high-salinity soil was 9.82% lower than that in low-salinity soil. Soil salinity also suppressed microbial community activity and diversity in the biochar, particularly fungi, likely contributing to the retardation of biochar aging. In addition, the barrier formed by soil mineral salts on the biochar surface further slowed the aging process. Additionally, temporal analysis revealed that over time, the oxidability of biochar increased due to the loss of labile carbon and the mineralization of organic matter, whereas the total carbon content decreased by approximately 20%. These findings enhance our understanding of biochar aging in saline soils and provide insights into its long-term environmental performance as a sustainable amendment.

Food waste digestate (FWD) composting is hindered by severe nitrogen loss, primarily through ammonia (NH₃) and nitrous oxide (N₂O) emissions. While biochar amendment is known to mitigate this loss, the optimal pyrolysis temperature to maximize conservation remains unclear. This study decouples the distinct influence of pyrolysis temperature (300, 400, and 800 °C) of hardwood biochar on nitrogen conservation by linking biochar properties to microbial community dynamics. A critical trade-off is revealed: 300 °C biochar maximized NH₃ reduction (39.2% vs. control, n = 2, p < 0.05) but was coincided with the enrichment of nirK/S-harboring denitrifiers (e.g., Luteimonas), posing a potential challenge from increased N₂O emissions. Conversely, 800 °C biochar achieved the greatest N₂O reduction (47.5% vs. control, n = 2, p < 0.05), an outcome consistent with suppressed microbial denitrification. Critically, biochar produced at 400 °C achieved an optimal balance, likely through enhanced NH₃ adsorption and the fostering of a microbial community correlated with lower N₂O emissions, which ultimately led to a 46.3% reduction in total nitrogen loss (vs. control, n = 2, p < 0.05), the highest performance among all treatments. This work guides the selection of biochar pyrolysis temperature toward targeted nitrogen conservation and sustainable FWD valorization.

Soil fauna activity is crucial for soil ecosystem functioning and health, but soil remediation techniques, such as biochar application, are seldom examined for their influence on soil fauna activity. This study systematically evaluated the effects of rice straw biochar application on the social behaviors of ants, Formica japonica, and elucidated how these behavioral changes enhance ant ecological functional traits. At moderate concentrations (2.5–5%), biochar significantly enhanced several ant colony functions: nest site selection specificity increased by 73.4%, nest architecture complexity improved by 2.8-fold, foraging efficiency accelerated by 2 fold, and social recognition accuracy enhanced by 3.5-fold. The improved colony performance was manifested through sophisticated behavioral responses, including strengthened territorial defense (3.5-fold increase in aggressive behavior duration) and enhanced intraspecific cooperation (4 fold increase in peaceful touch frequency). These behavioral enhancements coincided with specific soil physicochemical conditions at the application rate of 5% biochar. However, higher biochar doses (10%) reduced colony-level survival to 60 ± 5.44% and diminished functional enhancement of behavioral performance, in part due to the presence of persistent free radicals and high pH. Our results indicate that ant social behavior may be altered during soil remediation, which should be carefully considered prior to engineering practices.

Current rice production faces a critical trilemma of ensuring food security while conserving water and mitigating climate impacts. Conventional irrigation and nitrogen application sustain yields but simultaneously exacerbate water scarcity and environmental burden. Addressing this challenge requires urgently reconciling trade-offs among food security, water conservation, and climate regulation through optimized water and nitrogen management. Here, a two-year field experiment was conducted to evaluate the effects of alternate wetting and drying irrigation (AWD) and nitrogen-loaded biochar (NLB, 20 t ha⁻¹) on rice yield, water consumption, ammonia volatilization, and nitrogen distribution along the “soil–rice–plant” continuum. We found that AWD significantly reduced water consumption by 14.17–15.56% and increased rice yields by 2.23–5.11% compared to continuous flooding irrigation (CF). Notably, NLB addition under AWD further enhanced yields by 6.70–12.55% and reduced water use by 6.81–12.37% relative to the non-NLB control. Although NLB alone increased ammonia volatilization, this effect was mitigated by 11.38% when combined with AWD compared with CF. PLS-PM revealed that both NLB and AWD significantly and directly increased rice nitrogen accumulation and optimized water consumption, jointly contributing to yield gains. In conclusion, the AWD and NLB synergy is a next-generation strategy with the promise to simultaneously safeguard food security, lower environmental burden, and minimize water use—a triple win unattainable with conventional practices. These findings offer a scalable and replicable framework for sustainable rice production aligned with Sustainable Development Goals (SDGs) 2 (Zero Hunger), 6 (Clean Water), and 13 (Climate Action).

The escalating demand for sustainable agriculture necessitates innovative slow-release fertilizers (SRFs) that enhance nutrient efficiency while mitigating environmental impacts. This study presents a new green-synthesized nano-iron (tea extract iron nanoparticles, T-FeNPs) reinforced carboxymethyl cellulose/polyvinyl alcohol (CMC/PVA) composite coating for zeolite–biochar hybrid SRFs. T-FeNPs were synthesized using tea extract as a reducing agent and incorporated into CMC/PVA matrices. The nanocomposite coatings were applied to fertilizer cores comprising zeolite, nitrogen-phosphorus-potassium (NPK) compound fertilizer, and rice straw biochar (RSBC). Soil leaching tests demonstrated superior nutrient retention: CMC/PVA/0.5Fe-SRF reduced cumulative N and P release to 58.47% and 15.82%, respectively, outperforming unmodified CMC/PVA-SRF and compound NPK fertilizers. Mechanistic investigation uncovered that physical barrier enhancement via pore obstruction by T-FeNPs significantly impedes water ingress and nutrient ion diffusion. In tomato cultivation, the CMC/PVA/0.5Fe-SRF treatment maximized plant height, biomass, and water retention, attributed to sustained nutrient release. Soil analysis revealed enhanced total N, P, K, cation exchange capacity, and organic matter content. Economic analysis indicated a production cost of $562.02/ton for CMC/PVA/0.5Fe-SRF, with potential global GHG reductions of 35.69 Mt CO₂e in East Asia alone via improved nitrogen use efficiency. Overall, this work presents a scalable, eco-friendly strategy for enhancing fertilizer efficiency and soil health.

Biochar is increasingly promoted as a strategy for mitigating soil nitrous oxide (N₂O) emissions, yet its effect on the temperature sensitivity (Q₁₀) of N₂O emissions remains poorly understood. In this study, short-term incubation experiments were conducted using two contrasting soils (agricultural and forest soils) amended with two biochar types (wood- and rice husk-derived) at three application rates (0, 1%, and 3%) under three temperatures (10 °C, 20 °C, 30 °C). We investigated how biochar alters Q₁₀ of N₂O emissions and explored the underlying mechanisms. Results showed that cumulative N₂O emissions increased with temperature in both soils, with higher Q₁₀ values in forest soils (1.63–2.84) than in agricultural soils (1.13–1.63). Only high-rate wood biochar (WH) significantly changed Q₁₀, decreasing it in agricultural soils but increasing it in forest soils. In agricultural soils, WH strongly reduced NO₃⁻–N availability and minimized its temperature response, intensifying substrate limitation and lowering Q₁₀. In forest soils, biochar accelerated the decline of NH₄⁺–N and slowed the increase of NO₃⁻–N with temperature, suggesting tighter coupling between nitrification and nitrate-consuming processes. Although WH and high rate rice-husk biochar showed the smallest NO₃⁻-temperature slopes, the unique properties of WH (e.g., low ash content, higher aromaticity, and larger pore size) may have promoted short-term NO₃⁻ retention, thereby strengthening temperature-coupled nitrification–denitrification turnover, which likely contributed to the higher Q₁₀ observed under WH. Partial least squares path modeling (PLS-PM) confirmed that temperature exerted stronger total effects on N₂O emissions than biochar through changes in substrate availability, pH, and functional genes, while biochar acted as a secondary modulator. Overall, biochar regulated N₂O Q₁₀ through soil-specific pathways, highlighting the need for soil-specific biochar application strategies under future climate change scenarios.

Soil salinization severely limits crop productivity and ecosystem sustainability, particularly in arid and semi-arid regions. Here, we investigated the potential of targeted biochar amendments to rehabilitate saline-alkali soils and promote alfalfa (Medicago sativa) performance through integrative analyses of soil, plant, and rhizosphere microbiome. Two contrasting biochars—acid-modified biochar (AC-biochar, pH 2.3) and alkaline biochar (AL-biochar, pH 8.8)—were applied at 1%, 2%, and 5% (w/w) in controlled pot experiments. Our findings identified low-dose AC-biochar (1%) and high-dose AL-biochar (5%) as the most effective treatments for ameliorating soil geochemical constraints, including enhancing nutrient levels, reducing electrical conductivity, and modulating pH. These amendments significantly promoted alfalfa biomass and forage quality. A closer examination showed that AL-biochar primarily stimulated plant growth by enhancing amino acid metabolism, reactive oxygen species detoxification, and nitrogen assimilation, coupled with increased bacterial diversity and enrichment of beneficial taxa linked to nutrient cycling (e.g., Rhizobium and Firmicutes). In contrast, AC-biochar enhanced root development via activation of secondary metabolite biosynthesis (e.g., flavonoids and alkaloids) and recruitment of Actinobacteria known for pathogen suppression and organic matter decomposition. Integrative metabolic and microbiome analyses reveal that biochar-induced plant benefits transcend soil amelioration, exerting targeted regulation on plant physiology and rhizosphere ecology. These findings uncovered a previously underappreciated functional dichotomy in biochar effects and demonstrated the potential of precision biochar application as a scalable, sustainable approach for rehabilitating saline-alkali soils and improving crop resilience under environmental stress.

Biochar is increasingly recognized for its capacity to remediate acidifying soils, but the mechanisms through which it achieves long-term effects remain poorly understood. This five-year field study examined how biochar’s effects on soil chemistry propagate through biological systems to reshape soil function. We conducted a randomized field experiment comparing three biochar application rates (4.5, 11.25, and 22.5 t ha^–1) with lime and swine manure in an acidic paddy soil. Integrated soil microbiome, metagenomic, metaviromic, and metabolomic analyses assessed how amendments altered soil properties and their associations with microbial communities and metabolic functions. All amendments alleviated acidification (pH increased from 5.5 to 6.4) and reduced exchangeable aluminum (from 12.5 to 3.5 mg kg^–1). High-dose biochar (22.5 t ha⁻¹) initiated a mechanistic cascade absent under traditional amendments: improved soil chemistry drove restructuring of prokaryotic and viral communities toward nutrient-cycling phenotypes (enriching Chloroflexi, Planctomycetota, Algavirales, and Crassvirales), which in turn reshaped metagenomic functions and soil metabolite profiles. Specifically, biochar elevated genes related to nutrient exchange and cell–cell interactions while enriching lipids and terpenoids that support plant growth and long-term carbon stabilization. This coordinated restructuring of soil chemistry, microbial communities, and metabolic function did not occur under lime or manure. The findings demonstrate that biochar’s long-term superiority emerges from orchestrating sequential changes across the soil-microbe-metabolite system as an integrated whole. This mechanistic understanding provides novel insights for deploying biochar as an ecosystem restoration tool in acidifying agricultural systems.

Based on the concept of resource utilization, this study successfully prepared a green and highly efficient nitrogen-doped biochar catalyst (N-BC-800) using agricultural waste cotton hulls as a raw material. This catalyst was then applied to the ozone-catalyzed degradation of N,N-diethyl-meta-toluamide (DEET), a typical insect repellent in water bodies. The apparent second-order rate constant reached 2358 M⁻¹ s⁻¹, representing a 106-fold increase compared to the O₃ system alone, and a 25-fold increase compared to the O₃/BC system. Experimental characterization and theoretical analysis indicate that C=O groups and pyridinic N structures on the material surface serve as primary catalytic active sites. These synergistically promote ozone decomposition and generate highly reactive intermediates which are further converted into reactive oxygen species (ROS), significantly enhancing DEET degradation performance. This catalyst exhibits excellent stability and applicability in real aquatic environments. It demonstrates broad-spectrum degradation effects on multiple pollutants while significantly reducing the ecotoxicity of reaction byproducts. This study provides theoretical support and practical pathways for developing highly efficient, green ozone-catalyzed materials.

Urban greenspaces provide critical ecosystem and recreational services but are increasingly threatened by organic matter depletion, fertility decline, and nutrient cycle disruptions under rapid urbanization. Although protective measures like biochar and compost amendments are being widely implemented, their effectiveness across heterogenous urban greenspaces, and the underlying mechanisms governing these responses, remain poorly understood. In a manipulated field experiment across three urban greenspaces with contrasting intrinsic soil nutrient levels, we found that biochar and compost amendments enhanced soil carbon and nitrogen contents, with effects up to 14.4-fold stronger in nutrient-poor greenspace soils compared to nutrient-rich soils. Mechanistically, amendments in nutrient-poor sites elevated fungal diversity and the fungal-to-bacterial richness ratio, driving significant gains in soil carbon and nitrogen. In contrast, nutrient-rich sites exhibited declines in fungal diversity, network connectivity (< − 30%) and stability (− 2% to − 8%), but increased bacterial growth (> 4%) that accelerated carbon consumption, ultimately destabilizing soil carbon pools. These findings demonstrate that baseline soil nutrient status modulates amendment outcomes: in nutrient-poor soils, fungal dominance enhances carbon storage and soil fertility, whereas in nutrient-rich soils, nutrient surplus favors bacterial-driven carbon mineralization. Our study highlights fungi as pivotal drivers of soil restoration in urban greenspaces and underscores the need to prioritize nutrient-poor sites for biochar and compost interventions to maximize ecological benefits.

Biochar amendments show promise for mitigating accelerated antibiotic transport caused by macropore flow in soil, yet their effectiveness in such systems is poorly understood, lacking direct evidence differentiating biochar's role across macropore flow versus soil matrix infiltration. Using a novel macropore and matrix domains (dual-domain) separation apparatus, this study quantified the effect of biochar addition on the transport of weakly hydrophobic antibiotics, sulfadiazine (SDZ) and florfenicol (FFC), in soils under hydraulically isolated and connected domain conditions. Results suggested that biochar's efficacy is significantly amplified when hydraulic connectivity between the dual domains is present. In this state, it actively diverts antibiotics from macropore flow into the soil matrix infiltration, significantly reducing the total cumulative mass fluxes (CMFs) of SDZ from 0.72 ± 0.01 to 0.61 ± 0.00 and FFC from 0.81 ± 0.04 to 0.72 ± 0.02 (p < 0.05). Partial least squares structural equation modeling (PLS-SEM) subsequently revealed that biochar rewires the system’s causal pathways. The model showed that it leverages mobile carriers (dissolved organic matter and colloids) to create a powerful immobilizing sink in the matrix, while counteracting the advective flux traced by Br^–. These findings support the new hypothesis that biochar functions as a dynamic “biochar sorption pump” (BSP). This framework reframes biochar from a passive sink to an active flux regulator, providing a basis for designing precision remediation strategies based on soil hydraulic properties to protect vulnerable aquatic ecosystems.