Managing the 1.7 billion tons of pig manure produced globally each year presents a dual challenge for agriculture: preventing air and water pollution while retaining valuable nutrients for fertilizer. Aerobic composting is a common solution, but the process releases significant amounts of ammonia (NH₃) , an air pollutant, and nitrous oxide (N₂O) , a potent greenhouse gas. Researchers at the Chinese Academy of Agricultural Sciences have developed an effective and scalable solution by creating an iron-modified biochar (FeBC) that simultaneously cuts these emissions and improves compost quality.
The research team, led by Qingwen Zhang , prepared the additive by infusing biochar derived from corn stover with an iron solution. This simple modification produced a material with a 4.6-fold increase in specific surface area and a richer array of surface functional groups compared to untreated biochar. In a controlled composting experiment with pig manure, the addition of 5% FeBC dramatically reduced cumulative NH₃ emissions by 46.7% and N₂O emissions by 41.7% relative to the unamended control. The iron-fortified biochar also outperformed standard biochar, demonstrating its superior ability to lock nitrogen into the compost.
The enhanced physical and chemical properties of FeBC create a highly effective trap for nitrogen compounds. Its vast porous structure provides more sites for microbial colonization and direct chemical adsorption of nitrogenous gases. The iron component also plays an active role by helping to buffer the compost's pH, which prevents the conversion of stable ammonium into volatile ammonia gas. Furthermore, the FeBC-treated compost matured faster, maintained optimal temperatures for longer, and produced a final product with a higher germination index, indicating it was less toxic to plants and richer in nutrients.
To understand the biological drivers behind these improvements, the team used metagenomic analysis to map the genetic landscape of the microbial community. The analysis revealed that FeBC fundamentally alters the nitrogen cycle at the genetic level. It selectively enriched beneficial bacteria and upregulated genes responsible for nitrification (such as hao and nxrA), a process that converts volatile ammonia into stable nitrate. This locks nitrogen into the soil instead of allowing it to escape into the atmosphere.
Crucially, the additive also steered the denitrification pathway toward a more environmentally friendly outcome. FeBC suppressed the activity of genes (nirK and norB) that produce N₂O while boosting the abundance of the nosZ gene , which completes the final step of converting N₂O into harmless dinitrogen gas (N₂). This targeted microbial engineering explains the sharp drop in nitrous oxide emissions.
By integrating advanced material science with deep microbial analysis, this work provides a clear mechanistic roadmap for designing low-emission agricultural systems. The FeBC additive acts as both a physical sponge and a biological catalyst, creating a self-reinforcing system that stabilizes nitrogen. Structural equation modeling confirmed that FeBC strengthens the connections between the compost's physical environment and its microbial functions, leading to a more resilient and efficient process. This approach offers a practical way to transform agricultural waste into a high-value, sustainable fertilizer, supporting both food production and environmental health.
Corresponding Author:
Qingwen Zhang
Original Source:
https://doi.org/10.1007/s44246-026-00271-7
Contributions: All authors contributed to the study conception and design. Material preparation, data collection, and analysis were performed by Xinyuan Wei, Yu Liu, Yulong Shi, Xiaomei Xie, Chang Ma and Haoran Li. The first draft of the manuscript was written by Dong Wang. The review and editing of the manuscript were carried out by Qingwen Zhang and all authors commented on previous versions of the manuscript. All authors read and approved the final manuscript.
Carbon Research
Experimental study
Not applicable
Mitigating gaseous nitrogen emissions from pig manure composting via iron modified biochar: biotic and abiotic mechanisms
8-Jun-2026
The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper.