Biochar helps composting go greener by cutting greenhouse gas emissions

A global study has found that adding biochar to organic waste composting can significantly reduce emissions of potent greenhouse gases, offering a promising pathway for sustainable waste recycling and climate change mitigation.

Researchers from Nanjing Agricultural University and Sichuan University of Arts and Science analyzed data from 123 published studies covering more than 1,000 composting experiments worldwide. Their meta-analysis revealed that biochar reduced methane emissions by an average of 54 percent, nitrous oxide by 50 percent, and ammonia by 36 percent, while showing no significant effect on carbon dioxide release.

“Biochar acts like a sponge that improves aeration, absorbs harmful gases, and stabilizes nutrients,” said lead author Jingfan Xu. “This not only helps the environment but also produces higher-quality compost.”

Biochar is a carbon-rich material created by heating organic matter such as crop residues or wood in limited oxygen. When mixed into compost, it can alter microbial activity, enhance oxygen flow, and adsorb reactive nitrogen compounds that would otherwise be lost as ammonia or nitrous oxide. The new study is the first to quantitatively compare how different composting conditions and biochar characteristics influence these gas emissions.

The researchers found that the amount of biochar added is critical. Using 10 to 20 percent biochar by dry weight achieved the strongest reductions in methane, nitrous oxide, and ammonia. However, too little or too much biochar reduced the benefits. The compost’s physical and chemical properties also played a role: neutral to slightly alkaline pH (7.5–8.5), moderate moisture (55–65 percent), and low electrical conductivity favored optimal performance.

“By fine-tuning composting conditions, we can make organic waste recycling much more climate-friendly,” said senior author Professor Zhengqin Xiong. “Our analysis provides practical guidelines for farmers and waste managers to maximize the environmental benefits of biochar.”

Beyond emission reductions, biochar-enriched compost conserved nitrogen, improved pH balance, and helped stabilize carbon in the final product. These findings suggest that integrating biochar into composting systems could support both waste management and agricultural sustainability.

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Journal Reference: Xu J, Xiong Z. 2025. Biochar amendments mitigate trace gas emissions in organic waste composting: a meta-analysis. Nitrogen Cycling 1: e005  https://www.maxapress.com/article/doi/10.48130/nc-0025-0003  

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Nitrogen Cycling is a multidisciplinary platform for communicating advances in fundamental and applied research on the nitrogen cycle. It is dedicated to serving as an innovative, efficient, and professional platform for researchers in the field of nitrogen cycling worldwide to deliver findings from this rapidly expanding field of science.

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