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Scanning transmission electron microscopy and electron energy loss spectroscopy of organic coating on co-composted biochar. Micrographs were obtained from different ultra-thin sections of the same biochar particle. a, b STEM HAADF micrograph and EELS spectra of an ultra-thin section of cocomposted biochar revealing an organic coating. Position 1: biochar with N and O below detection limit of EELS; 2: epoxy resin; 3: empty hole (resin did not penetrate this pore); 4: gold that was sputtered onto the biochar particle before embedding to identify the sample surface; 5: organic coating, porous appearance, contains N and O according to EELS spectra shown in b; 6 and 7: Location of EELS sum spectra shown in b. b EELS spectra revealing only minor differences in C speciation between biochar (red) and organic coating (blue), but considerably increased content of N in the coating. Letters indicate absorption edge (K shell) of C, N and O. c Closeup on a region of thick (~120 nm) organic coating, probably located inside a biochar pore (no gold coating detectable). d C-K near edge EELS spectrum of biochar matrix and coating as marked in c showing a peak shift of the C = C 1s–π* transition (1) of aromatic carbon by ~0.5 eV (284.9–285.5 eV). C–C 2s-2pz σ* transition (2) was not altered (291.2 eV). e N-K near edge EELS spectrum of coating as marked in c showing (1) imine N 1s–π* transition at 399–400 eV; (2) amide N 1s–3p/π* transition at 401.3 eV; (3) nitro N 1s–π* transition at 403.6 eV; (4) corresponds to HC ≡ N* transition at 406.8 eV with σ* resonance position at 420.8 eV63. f Organic coating formed at a biochar surface that is rich in Ca hotspots of bright appearance in the HAADF micrograph. Coating is shearing off as an artefact of the mechanical force applied during sample preparation, most likely by the microtome, which indicates a rather plastic nature of the coating compared to the biochar that broke (lower part of the micrograph). Thickness of coating varies between ~20 and 50 nm and the presence of gold indicates a semi-exposed position in the original biochar particle. g EELS spectra from regions indicated in f showing the peak shift of the C = C 1s–π* transition and the presence of Ca in the region of the bright spot in the outermost region of the biochar
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Amending soil with biochar (pyrolized biomass) is suggested as a globally applicable approach to address climate change and soil degradation by carbon sequestration, reducing soil-borne greenhouse-gas emissions and increasing soil nutrient retention. Biochar was shown to promote plant growth, especially when combined with nutrient-rich organic matt...
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... Soil pH, TN, and AN content were highest in the BC5 treatment, suggesting that the addition of high concentrations of REE-rich biochar is more suitable for improving the soil environment than the addition of low concentrations of REE-rich biochar, which is in line with the results reported by Liu et al. [29]. The reason for this may be that biochar itself is rich in organic matter and mineral elements, which can directly increase soil nutrient levels when applied to the soil [30]. Simultaneously, because it has a complex void structure and strong adsorption capacity [27], biochar can help reduce soil nutrient loss and effectively conserve nutrients. ...
Rare earth elements (REEs) are key resources of strategic importance, but pollution has increased due to uncontrolled mining. Although heavy metal hyperaccumulating plants are environmentally friendly, they require strict control during post-treatment, or they may cause secondary pollution. Therefore, their safe disposal plays a key role in the ecological restoration of REE mines. In this study, rare earth element (REE)-rich biochar was produced by pyrolyzing the REE hyperaccumulator Dicranopteris pedata. This biochar was then applied to the Citrus grandis (L.) Osbeck. cv. Guanximiyou soil amendment experiment to evaluate its effects on soil physicochemical properties and microbial indicators. Four treatments were established: CK (0% REE-rich biochar), BC1 (1% REE-rich biochar), BC3 (3% REE-rich biochar), and BC5 (5% REE-rich biochar). The BC5 treatment decreased soil REE bioavailability, thereby preventing REE pollution. The BC5 treatment also demonstrated the highest efficacy in improving soil total organic carbon (229.11%), total nitrogen (53.92%), total phosphorus (55.61%), total potassium (55.50%), available nitrogen (14.76%), available phosphorus (46.79%), and available potassium (159.42%) contents compared to CK. Furthermore, soil enzyme activities were significantly increased by BC5 treatment (p < 0.05). At the bacterial phylum level of classification, the bacterial diversity index (Chao1 and Shannon) exhibited elevated levels under BC5 conditions. Furthermore, the Chao1 index of fungal diversity exhibited a substantial augmentation of 55.67% (p < 0.05) in the BC5 treatment in comparison to the CK, and also significantly higher than the other treatments (p < 0.05). Our study showed that the composition of soil microorganisms was altered by REE-rich biochar. Proteobacteria, Acidobacteria, Actinobacteriota, and Chloroflexi are dominant among bacteria, while Ascomycota is dominant among fungi. Mantel and redundancy analyses showed that the most important environmental factor affecting the structure of soil microbial communities was pH, especially in the case of bacteria. In summary, this study showed that the application of 5% REE-rich biochar provided the best improvement in soil physicochemical properties and microbial diversity. These findings highlight its potential for soil remediation and provide new ideas for recycling heavy metal hyperaccumulating plant waste.
... On the other hand, the 7.5% BC(SD + Z) variant exhibited significantly decreased URE values as compared to variants amended with all other (7.5%) biochar types. Presumably, the BC(SD + Z)-mediated SOM stabilization and protection from decomposition (due to recalcitrancy) was coupled with rigid coating of pyrolyzed matter with more complex organic compounds [112] associated with zeolite. This verifies the hypothesis 4, which proposed increased SOM recalcitrance and stabilization of nutrients by BC(SD + Z) biochar, was done. ...
The thermal conversion of municipal sewage sludge (MSS) offers significant potential for sustainable waste management, particularly through the production of biochar. This study investigates the properties and soil application effects of three biochar types produced via pyrolysis: (i) pure sewage sludge (100%), (ii) sewage sludge blended with sawdust (50%+50%), and (iii) sewage sludge combined with sawdust and zeolite (50%+45%+5%). These biochars were applied at rates of 2.5% and 7.5% (w/w) to arable soil and assessed in an 8-week greenhouse experiment using lettuce (Lactuca sativa L. var. Brilant) as a model crop. The sewage sludge biochar was characterized by high nitrogen, phosphorus, and water-extractable calcium but exhibited low organic matter and organic carbon content. It enhanced soil enzyme activities related to carbon and nitrogen mineralization without affecting microbial respiration. However, at 7.5% application rate, this biochar caused the highest chlorophyll b content in lettuce, despite acidifying the soil. Adding sawdust to the pyrolysis feedstock significantly increased organic matter, organic carbon (with reduced recalcitrance), and the C: N ratio of biochar. This biochar formulation promoted microbial activity (as indicated by changes in soil respiration) and nutrient cycling, particularly through increased glucosidase activity. Conversely, addition of zeolite to the pyrolysis feedstock reduced the organic matter and organic carbon content while increasing biochar recalcitrance and nutrient immobilization, particularly of sulfur, ammonium, phosphorus, and calcium. At the 7.5% dose, the sawdust + zeolite-enriched biochar improved soil pH and potentially enhanced nutrient retention. However, it did not stimulate microbial enzyme activity or respiration, leading to lower photosynthetic pigment levels and reduced biomassin lettuce, especially at higher application rate. For short-term soil applications under the conditions of this pot trial, the sewage sludge-sawdust biochar demonstrated the most beneficial effects, rapidly stimulating microbial activity and nutrient transformation. In contrast, the sewage sludge-sawdust-zeolite biochar limited nutrient availability and plant growth, suggesting it may be less suitable for immediate soil and plant nutrition. Long-term studies are needed to fully assess the implications of these biochar types for sustainable agriculture. This study highlights the importance of feedstock composition and selection in tailoring biochar properties to meet specific soil and crop requirements.
... Biochar has a large specific surface area, a rich porous structure, and surface functional groups, which help inhibit the proliferation and diffusion of ARGs through absorption and decomposition; these characteristics also influence bacterial communities and horizontal gene transfer via MGEs, leading to a decrease in the level of ARGs (Fu et al., 2021;Fang et al., 2022). Composted biochar has high porosity, numerous pore structures, and small surface pores (Hagemann et al., 2017), which may further enhance its inhibitory effect on the proliferation of ARGs in soils. The decrease of ARGs in soils lays a strong basis for decreasing the accumulation of ARGs in vegetables. ...
... The small-sized biochar with numerous pore structures can inhibit the horizontal gene transfer of ARGs well (Tong et al., 2023b). Meanwhile, biochar showed increased pores and reduced pore size after being composted (Hagemann et al., 2017), enhancing the inhibitory effects described above. The intI1 and intI2 exhibited a significant positive correlation with most ARGs (Supplementary Figure S1). ...
The transfer of antibiotic resistance genes (ARGs) from soils to vegetables negatively impacts human health. This study explored the effects of the high-dose (18.73 t/ha) application of traditional compost (TC) and composts produced through the co-composting of traditional materials with large-sized (5–10 mm) biochar-amended compost (LBTC) or small-sized (< 0.074 mm) biochar-amended compost (SBTC) on the distribution of ARGs in a soil–cucumber system were explored. Results indicated that the SBTC group had the highest soil nitrogen, phosphorus, and potassium contents, followed by the LBTC, TC, and control treatment groups. These findings aligned with the quality and weight of harvested cucumbers. Bacterial community diversity decreased in compost-fertilized soils. Compared with their preexperimental values in soils, the total absolute abundances of ARGs and mobile genetic elements (MGEs) increased by 23.88 and 6.66 times, respectively, in the control treatment group; by 5.59 and 5.23 times, respectively, in the TC group; by 5.50 and 1.81 times, respectively, in the LBTC group; and by 5.49 and 0.47 times, respectively, in the SBTC group. Compared with those in the control treatment group, the absolute abundance of ermB, ermT, gyrA, qnrS, tetC, and intI1 decreased by 6–100% in the soil of the SBTC group. Compost application to soils significantly decreased ARG abundance in cucumbers; SBTC had the most significant effect and reduced the number of host bacteria at the phylum level from four to three. Nutrient levels in soils were important factors influencing the migration of ARGs from soils to cucumbers. In summary, when compared to other composts, the high-dose (18.73 t/ha) application of SBTC is more effective at reducing the risk of the accumulation and transfer of ARGs in the soil–cucumber system.
... A meta-analysis of biochar applications has reported increases in crop yields, particularly in degraded or nutrient-poor soils . The enhancement in crop yields resulting from biochar application can be attributed to several key mechanisms, including improved nutrient retention (Hagemann et al., 2017) and regulation of soil pH (Shetty and Prakash, 2020), both of which contribute to enhanced soil fertility and plant growth. Biochar's porous structure and high surface area enhance the adsorption of essential nutrients such as N and P, reducing nutrient losses through leaching (Gelardi et al., 2021;Lu et al., 2022). ...
This review critically evaluates biomass-derived chars produced via thermochemical processes, i.e., pyrolysis, gasification, and hydrothermal carbonization, as potential alternatives to synthetic fertilizers. Among the three biomass-derived chars, biochar stands out as the most viable option for soil amendment due to its high stability, nutrient retention capacity, and long-term carbon sequestration benefits.
... Biochar is a stable, carbon-rich organic material produced through pyrolysis-a process conducted at high temperature under oxygen-limited conditions (Shabir et al. 2024;Lu et al. 2025;Wang et al. 2025). While biochar is commonly used to enhance soil quality and increase carbon sequestration due to its porous structure, high adsorption capacity, and strong cation exchange capacity (Hagemann et al. 2017;Weng et al. 2017Weng et al. , 2022Cheng et al. 2024a), its role in reducing soil N 2 O emissions is gaining attention. Notably, biochar application is considered a promising approach for reducing N 2 O effluxes from soils (Kaur et al. 2022;Cheng et al. 2024b). ...
Subtropical forests are significant contributors to N2O emissions with consequences for climate regulation. Biochar application has emerged as a promising strategy to mitigate soil N2O emissions, yet its effects and the underlying mechanisms under nitrogen (N) deposition in subtropical forests remain poorly understood. A comprehensive 3-year field study within a subtropical forest reveals that N deposition led to a significant increase in soil N2O emissions by 14.6–25.1% annually. However, biochar application resulted in a substantial reduction of these emissions, ranging from 8.0–20.8% each year. Notably, the mitigation effect of biochar was particularly pronounced when N deposition was occurring, leading to an even greater reduction in N2O emissions by 14.2–22.0% annually. This mitigation effect is attributed to biochar’s capacity to lower the nitrification and denitrification rates of soil via reducing levels of ammonium N and water-soluble organic N. Additionally, biochar decreased the abundance of critical microbial genes, including AOAamoA, nirK and nirS, and reduced the activity of key enzymes such as nitrate and nitrite reductase. These findings highlight the potential of straw biochar to effectively mitigate soil N2O emissions in subtropical forests experiencing N deposition, offering important insights for supporting ecosystem sustainability under global climate change.
... This, in turn, leads to the consequent ability of the material to exchange matter and nutrients, after its application for soil conditioning, and to sequester potential pollutant species as well. Therefore, as a further development of our previous works [15,18,29,30], in the present study, we examined the oxidation of a poplar biochar (PB) obtained at a high pyrolysis temperature (1200 • C) with three different common oxidation systems. In particular, the "piranha mixture" (H 2 O 2 and conc. ...
... It is important to stress that the operational conditions have a significant influence on the reaction course, in terms of final yields and extent of functionalization. Reactions were carried out at various temperatures (0 • C, 27 • C, 60 • C, and 90 • C) and reaction times (10,30,60,90, and 180 min), with 60 • C for 30 min serving as the standard condition. The reaction conditions used and the corresponding yields are summarized in Table 1. ...
This study investigates the functionalization of a poplar biochar (PB), obtained by high-temperature pyrolysis, under oxidative conditions typically used in organic synthesis. In particular, concentrated nitric acid, a sulfonitric mixture and a piranha mixture were applied as oxidants at different temperatures and reaction times. In order to assess the outcome of the reaction conditions on the characteristics of the resultant products, these were characterized by a combination of imaging (SEM), spectroscopic (ATR-FTIR, RAMAN) and FFC-NMR relaxometric techniques. The latter techniques, rationalized in terms of the Kohlrausch-type stretched exponential kinetic model, were analyzed using a recently developed heuristic Monte Carlo method, providing insights into the water dynamics within material pore networks. Additionally, the water-holding capacity of the modified biochars and their abilities to adsorb some model dyes were evaluated. The results clarify the relationship between oxidative treatment conditions and biochar properties, highlighting their impact on both structural modifications and water dynamics within the porous network, and enabling us to identify the best reaction conditions for optimizing the features of the oxidized product.
... Biochar application improved the EC, OM, AP, and AK of RCA regardless of biochar types and application ratios (Table 1). Upon application, biochar improved nutrient retention by promoting the development of an organic layer which was enhanced by hydrophilicity and redox activity (Hagemann et al., 2017). The abundant carbon content in biochar was the reason for the significant increase in soil organic carbon (Gautam et al., 2021). ...
HIGHLIGHTS • Biochar application enhanced the nutrients of recycled concrete aggregates. • Higher salinity caused by biochar application inhibits urease and phosphatase activities. • Biochar addition improves certain bacterial species that promote plant growth. ABSTRACT: The substantial generation of building waste had precipitated significant environmental issues in China, attributable to urban expansion. Recycled concrete aggregate (RCA) produced from building waste had been used as an alternative material in green roofs as substrates. However, the biological dynamics of RCA are unknown. Thus, the column test was performed to investigate the effects of different biochar types and application ratios on the biochemical properties and bacterial communities of RCA. Results show that the nutrients of RCA have been improved by biochar addition regardless of biochar types and application ratios. This led to the increase in plant weight and height by at least 227% and 38% in biochar amended RCA. However, biochar application reduced bacterial richness and α-diversity, while enhancing plant growth. This indicated that biochar application directly improves certain bacterial species that promote plant growth and productivity. Biochar application reduced the Proteobacteria abundance and enhanced the percentage of Acidobacteriota in RCA, indicating that biochar application shaped the bacterial communities into raw soil composition. The outcome of this research suggests that biochar application improved RCA biochemical performance as a substrate for green roofs, which provides a potential method to consume substantial RCA.
... BC contains both micropores (<2 nm) and mesopores, stores dissolved substances, and retains moisture, thereby supporting microbial growth [50][51][52]. Its alkaline nature can enhance soil pH, creating favorable conditions for specific microbial populations [53,54]. Consistent with previous findings [51], BC application significantly increased soil MBC, MBN, and UA, highlighting its ability to enhance microbial biomass and enzyme activity compared to RS and CK treatments. ...
This study assessed the impact of planting techniques and short-term organic additions on soil quality, enzyme activity, and bacterial community composition. Biochar (BC) amendment substantially enhanced the ACE, Chao 1, and Shannon indices in direct-seeded rice (DS). Principal coordinate analysis (PCoA) and dissimilarity distances confirmed significant differences in the rhizosphere bacterial community composition associated with planting methods and organic applications. At the phylum level, transplanting (TT) significantly increased the abundance of Proteobacteria, Planctomycetes, Bacteroidetes, Firmicutes, and Verrucomicrobia, whereas DS significantly reduced the abundance of Acidobacteria, Chloroflexi, Actinobacteria, Gemmatimonadetes, and WPS-2. Rice straw (RS) application was associated with increased Proteobacteria, Acidobacteria, Chloroflexi, and Gammaproteobacteria, while BC application improved Bacteroidetes, Firmicutes, and Verrucomicrobia. Planting methods and organic amendments were also observed to affect soil enzyme activities and physicochemical properties. DS was associated with an increase in microbial biomass nitrogen (MBN) and carbon (MBC), cellulase activities (CA), total phosphorus (TP), available nitrogen (AN), and available potassium (AK), while TT significantly increased urease activities (UA). Compared to BC and the control (CK), RS significantly increased CA, AN, and available phosphorus (AP). RDA ordination plots were used to examine the interactions between soil bacterial communities and soil physicochemical properties; planting techniques and organic additions had different effects on soil bacterial communities. Compared to RS and CK, BC enhanced MBN, MBC, UA, and AK. According to Pearson’s correlation analysis, Chloroflexi levels were positively associated with those of organic carbon (OC), MBN, and MBC. OC, TP, MBN, and CA positively correlated with gemmatimonadetes. In conclusion, these data reveal that planting practices and short-term organic inputs alter soil’s physicochemical parameters, enzyme activity, and microbial community composition.
... The changes in pH before and after composting were small, and biochar addition imposed a negligible effect on the overall pH in the composting. The pH of the compost first decreased temporarily, possibly as a result of the large amount of volatile fatty acids produced in the early period of composting [27], with a subsequent overall increase in pH followed by a decrease at the middle and late periods. At the middle and late periods, with the reduction of ammonia volatilization, nitrification under the CK and BC treatments was greatly enhanced, which led to a gradual decrease in the pH [28]. ...
Food waste digestate (FWD), as a low-polluting and high-nutrient waste, has a great potential for resource utilization. Aerobic fermentation composting technology is very suitable for the disposal of FWD, due to its reduction and hygienization characteristics. Biochar can reduce odor emissions and enhance compost quality with its suitable spatial structure and porosity. In this study, the basic physicochemical indexes and microbial abundance of compost were monitored using the windrow composting method, and PICRUSt2 and FAPROTAX were applied to analyze the changes in metabolic functions of microorganisms. The results indicated that biochar prolonged the high-temperature period and improved organic matter degradation. The dominant bacteria in compost were Proteobacteria, Actinobacteriota, Firmicutes and Bacteroidota. Pseudofulvimonas and Burkholderiales are unique to biochar composting and are related to the degradation of composted organic matter and nitrogen cycling. Acidobacteriota positively affected compost decomposition. Gemmatimonadota and Chloroflexi promoted compost decomposition only after biochar addition. Metabolic functional analysis revealed that biochar promoted metabolic pathways and biosynthesis of secondary metabolites. Biochar enhanced the interaction among temperature, electrical conductivity (EC) and pH during FWD composting, which synergistically caused changes in the bacterial community and C/N ratio, further increasing the compost decomposition efficiency. Among these factors, the C/N was the main driver of biochar influence on FWD compost maturation.
... In contrast, BCH exhibited a comparatively lower GreyW contribution. Its reduced nitrogen concentration-adequate for olive cultivation given the application rates-combined with its ability to improve soil structure and nutrient retention [60], effectively limited nitrogen leaching losses and thus reduced the GreyW parameter. ...
This modeling study evaluates the combined effects of organic fertilization and irrigation regimes on olive productivity and environmental sustainability in southern Italy. Field experiments were conducted in an organic olive grove (cv. Leccino) under Mediterranean conditions, testing four organic fertilization treatments—biochar (BCH), compost (CMP), dried blood (DB), and a commercial organic fertilizer (CTR)—and two irrigation strategies. The CropWat model was employed to simulate additional irrigation scenarios, ranging from full irrigation (Full; 100% ETc) to rainfed conditions. Results showed that biochar-treated olive groves achieved the highest yields (up to 3756 kg ha⁻¹ under full irrigation), outperforming other treatments, with yields of 3191 kg ha⁻¹ (CMP), 2590 kg ha⁻¹ (DB), and 2110 kg ha⁻¹ (CTR). Deficit irrigation strategies, such as ceasing irrigation during the pit-hardening stage (Red_Farm; 1160 m³ ha⁻¹), reduced water use by 67% compared to Full (3600 m³ ha⁻¹) while maintaining satisfactory yields (3070 kg ha⁻¹ vs. 2035 kg ha⁻¹ on average across all fertilization treatments). Water footprint (WFP) analysis revealed that BCH consistently achieved the lowest WFP values (e.g., 1220 m³ t⁻¹ under Full and 687 m³ t⁻¹ under rainfed conditions), outperforming CTR (1605 m³ t⁻¹), CMP (1645 m³ t⁻¹), and DB (1846 m³ t⁻¹) under full irrigation and 810 m³ t⁻¹, 1219 m³ t⁻¹, and 1147 m³ t⁻¹ with no irrigation water supply. Incremental water productivity (IRincr) and marginal water footprint efficiency (WFPincr) further demonstrated that BCH optimized both productivity and environmental sustainability, with IRincr values of 0.55 kg m⁻³ and WFPincr values of 1.58 m³ kg⁻¹ (averaged for all water regimes), better than CTR (0.40 kg m⁻³ and 2.14 m³ kg⁻¹), CMP (0.46 kg m⁻³ and 1.93 m³ kg⁻¹), and DB (0.38 kg m⁻³ and 2.32 m³ kg⁻¹). An aggregated scoring system, based on standardized and normalized data, ranked BCH under the Red_Farm irrigation strategy as the most effective management approach, achieving the highest overall score compared to the other fertilizer treatments in combination with the different irrigation strategies, thereby balancing high yields with significant water savings.
