This study investigated the impacts of biochar addition on N conversion, humification, and bacterial community during Flammulina velutipes waste composting. The mixture of chicken manure and Flammulina velutipes waste was 4:6 (dry weight basis). The biochar was added into the mixture and mixed thoroughly at ratios of 0, 2.5, 5, and 7.5% (w/w) and labeled as CK, T1, T2, and T3, respectively. The results showed that the biochar treatment significantly improved the compost maturity by increasing humic substances and the conversion of NH₄⁺-N to NO₃⁻-N. With the increase in biochar supplemental level, the abundance, diversity, and uniformity of the microbial community were improved. The dominant taxa were Firmicutes, Bacteroidota, Actinobacteriota, Proteobacteria, and Gemmatimonadota, especially the Firmicutes and Bacteroidota. Biochar addition facilitated the proliferation of thermophilic bacteria such as Bacillus, Actinobacteriota, Parapedobacter, and Sphingobacterium, leading to enhanced organic decomposition to increase humus. The findings of this study highlighted the positive effects of biochar addition on the composting mixture of chicken manure and Flammulina velutipes waste. These results can help to produce high-quality biochar composting products by balancing organic decomposition and humification based on the bacterial community.

The rapid expansion of aquaculture generates vast quantities of hyperhydrated organic waste (e.g., eel feces), posing a severe waste management challenge due to its recalcitrance and high disposal costs. This study presents a circular bio-strategy using black soldier fly (BSF, Hermetia illucens) larvae to synergistically convert aquaculture waste and agro-industrial residue (Flammulina velutipes substrate) within a closed-loop system. The process achieved 92.6 % waste utilization efficiency, yielding two valuable co-products: First, BSF larvae accumulated nutrient-rich biomass (17.9 % crude protein, 8.03 % lauric acid). As a 1.0 % supplement in broiler diets, it significantly enhanced feed efficiency by 2.6 % and increased 42-day body weight by 7.5 % (P < 0.01), demonstrating a viable fishmeal alternative. Second, BSF frass was composted into a superior organic fertilizer, which outperformed conventional composting by reducing NH₃ emissions by 34 % (P < 0.001) and increasing total nitrogen retention by 15.3 %, attributed to pH modulation and chitin-NH₄⁺ complexation. The frass also enhanced phosphorus (7.05 %) and potassium (2.76 %) bioavailability. Metagenomics analysis revealed that frass inoculation enriched functional microbes (Azoarcus, LDA > 2.5; Roseisolibacter) driving synchronized nitrogen fixation and phosphate solubilization. Field application of the compost boosted tomato yields by 12.1 % (P < 0.05) and improved fruit quality (vitamin C + 18.6 %, soluble sugars + 20 %). This work establishes a scalable waste-to-resource paradigm that concurrently addresses waste management, livestock feed security, and sustainable crop intensification.

This study elucidates the synergistic regulatory mechanisms of biochar-amended chicken manure and mushroom residue compost (BCM) on soil microbial communities and nutrient cycling in the extra-rhizosphere, while evaluating its potential for sustainable agricultural waste recycling. Methods: We conducted a 50-day composting trial using five biochar application rates (0–7%). Assessed parameters included compost maturity (C/N ratio), nutrient content (NO ₃ ⁻ -N, available phosphorus [AP], soil organic matter [SOM]), phosphatase and catalase activities, microbial community composition, and metabolic pathways. We performed Redundancy analysis (RDA) to correlate SOM/AP dynamics with microbial diversity and functional pathways. Results: At 5–7% biochar, compost maturity improved significantly, with C/N ratios of 15.6–18.2 and 2.2-4.0-fold increases in NO ₃ ⁻ -N (1.41 mg/g), AP (50.09 mg/kg), and SOM (166.11 g/kg). Enzymatic activities (phosphatase: 9.81 mg/g·24 h; catalase: 83.08 µmol/g·24 h) correlated strongly with SOM/AP (R ² = 0.71–0.82). Biochar enriched Proteobacteria (34.1%) and Actinobacteriota (15.2%), suppressed Halophiles ( Halomonas reduced by 52%), and enhanced carbon metabolism and oxidative phosphorylation pathways. RDA identified SOM/AP as a key driver of microbial diversity (R ² = 0.91). The 5% biochar dose optimized nutrient retention (37–59% increases in AP, Available potassium [AK], NO ₃ ⁻ -N) while maintaining microbial diversity, outperforming higher doses. Conclusions: This study demonstrates biochar’s dual role in reshaping extra-rhizosphere microbial ecology and nutrient dynamics, offering a precision agriculture strategy for sustainable waste recycling and circular economy practices. The 5% biochar dosage proved optimal, enhancing nutrient cycling and microbial activity while mitigating halophilic microbial suppression. Graphical Abstract