In a recent study published in Soil & Environmental Health, Keiji Jindo, Tomonori Sonoki, and Miguel A. Sánchez-Monedero explored the effectiveness of biocharBiochar is a carbon-rich material created from biomass decomposition in low-oxygen conditions. It has important applications in environmental remediation, soil improvement, agriculture, carbon sequestration, energy storage, and sustainable materials, promoting efficiency and reducing waste in various contexts while addressing climate change challenges. More in improving composting processes, specifically focusing on its ability to stabilize organic matter and reduce methane emissions. Their findings highlight biochar as a promising additive that offers dual benefits: environmental protection through greenhouse gas reduction and enhanced compost quality for sustainable agriculture.

Methane (CH4​) is a potent greenhouse gas, and its emission during composting is a significant concern. The research demonstrated that biochar dramatically reduces CH4​ emissions. In poultry manure (PM) composting, biochar addition led to a 4.6-fold decrease in CH4​ emissions compared to PM without biochar. Similarly, in cattle manure (CM) composting, CH4​ emissions were reduced by approximately 3.7 times with biochar. This reduction is primarily attributed to biochar’s porous structure, which improves aeration within the compost piles, thereby hindering the anaerobic conditions that favor CH4​ production by methanogenic archaea. The study also noted a secondary phase of CH4​ emission around day 42, which was also mitigated by biochar.

Beyond methane mitigation, biochar positively influences organic matter stabilization, particularly the degradation of lignin. Lignin is a complex, recalcitrant carbon compound that is difficult to break down. The study revealed that biochar-amended composts showed approximately 1.5 times greater lignin degradation than control groups. Specifically, 29.0% of lignin was degraded in poultry manure with biochar (PM+B) and 10.8% in cattle manure with biochar (CM+B). This enhanced degradation is linked to improved aerobic conditions and the proliferation of lignin-degrading microorganisms like actinomycetes and white-rot fungi, which produce necessary oxidative enzymes. The presence of biochar also increased the thermal stability of the compost, with the W2​/W1​ ratio indicating an increase in stability by 2.8-fold in PM+B and 4.4-fold in CM+B at the initial stage, and even more pronounced effects at the final stage (2.6-fold for PM+B and 4.7-fold for CM+B). The researchers also investigated changes in other carbon fractions and microbial activity. While biochar enhanced overall carbon transformation, composts without biochar retained higher levels of easily degradable compounds like total dissolved carbon, carbohydrates, and water-soluble polyphenols. This is because biochar promotes the rapid decomposition and humification of these labile carbons into more stable forms. Additionally, ATP and dehydrogenase activity, indicators of microbial activity, were generally higher in composts without biochar, likely due to the greater availability of easily degradable substrates. However, alkaline phosphatase activity, an enzyme involved in phosphorus cycling, was higher in biochar-amended composts, possibly due to biochar’s influence on microbial communities and pHpH is a measure of how acidic or alkaline a substance is. A pH of 7 is neutral, while lower pH values indicate acidity and higher values indicate alkalinity. Biochars are normally alkaline and can influence soil pH, often increasing it, which can be beneficial More conditions favorable for this enzyme.

Redundancy analysis (RDA) further elucidated the complex interactions within the composting environment. During the thermophilic stage, CH4​ emissions were strongly associated with the methanogenesis gene (mcrA), fungi, and total nitrogen, while carbon dioxide (CO2​) correlated with bulk density and Gram-negative bacteria. Biochar’s ability to reduce bulk density improved aeration, thereby suppressing CH4​ production and promoting CO2​ release. In the final composting stage, maturity indices like humification index (HI) and polymerization index (PZ) were linked to physicochemical traits (e.g., total nitrogen, ammonium, bulk density) and microbial variables, underscoring the combined role of these factors in achieving stable compost.

This study provides compelling evidence that biochar serves as a valuable amendment in composting, not only for significantly reducing harmful methane emissions but also for enhancing the quality and stability of the final compost product. These improvements hold great promise for bolstering soil health and contributing to more sustainable agricultural practices.

Source: Jindo, K., Sonoki, T., & Sánchez-Monedero, M. A. (2025). Stabilizing organic matter and reducing methane emissions in composting with biochar to strengthen the role of compost in soil health. Soil & Environmental Health.