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A new study by researchers from Sichuan Agricultural University and international collaborators provides the most comprehensive evidence to date that biochar, a charcoal-like substance made from organic materials, plays a crucial role in faster, cleaner composting.

By analyzing data from 125 studies across the world, the research team showed that adding biochar to composting systems significantly boosts compost quality while slashing harmful greenhouse gas emissions. The findings, in Biochar X, could help scale up sustainable waste management and climate-friendly agriculture.

"Biochar doesn't just make compost richer; it also makes the process cleaner," said lead author Jianmei Zou. "We found that the right kind of biochar can speed up decomposition, reduce harmful gases, and produce a more stable, mature product for farmers."

The meta-analysis combined 269 observations to pinpoint the factors that matter most. On average, biochar-amended compost improved the germination index—a measure of compost safety and nutrient balance—by over 25%.

It also reduced key pollutants: ammonia (NH₃) fell by nearly 48%, methane (CH₄) by 51%, and nitrous oxide (N₂O) by 43%. These gases are major contributors to global warming when released from organic waste.

Importantly, the study identified optimal conditions for composting success. The most effective biochar came from straw heated to about 400°C, with moderate porosity and a carbon-to-nitrogen ratio between 100 and 200.

When used at an application rate of 12% and combined with compost made from sewage sludge at about 55–60% moisture, these conditions yielded the best results.

Biochar's microscopic pores improve aeration, hold nutrients, and create a favorable habitat for beneficial microbes. These interactions accelerate the composting process, limit nitrogen loss, and convert waste into nutrient-rich organic fertilizer.

The researchers also ranked which factors exerted the greatest influence on compost success. Pore volume, biochar source, and amendment rate topped the list.

"This ranking framework helps producers make smarter choices when designing composting systems," said co-author Fei Shen. "It turns a complex biological process into something predictable and scalable."

The study adds to growing evidence that biochar can help meet global sustainability goals by cutting waste emissions and improving soil fertility.

By translating laboratory science into practical composting strategies, these findings could support greener agriculture and more efficient recycling of organic waste worldwide.