Researchers investigated the role of biochar conductivity in regulating methane (CH4) emissions from paddy soils. Their study, published in the journal Biochar, highlights that biochar with higher electrical conductivity significantly increases CH4 production by enhancing electron transfer mediated by dissolved organic matter (DOM).
Image Credit: Rene Notenbomer/Shutterstock.com
The findings clearly explain how conductive biochar drives methanogenesis, offering practical insights for sustainable soil management and greenhouse gas mitigation strategies in agriculture, mainly in rice cultivation.
The Role of Biochar in Agricultural Sustainability
Biochar is a carbon-rich material produced through the pyrolysis of biomass under limited oxygen conditions. Its high surface area, porosity, and conductivity make it valuable for improving soil fertility, retaining water, sequestering carbon, and mitigating greenhouse gas emissions. Paddy soils contribute nearly 30% of global agricultural CH4 emissions, a greenhouse gas that is 27.5 times more effective than carbon dioxide (CO2) at trapping heat.
CH4 production in these soils occurs through various mechanisms: hydrogenotrophic, acetoclastic, methylotrophic, and electron-mediated methanogenesis. In this context, previous studies have shown mixed results regarding biochar’s effects on CH4 emissions, highlighting the need to clarify how conductivity influences these processes.
Investigating Biochar Conductivity Effects
Researchers focused on how biochar conductivity affects CH4 generation in paddy soils, emphasizing electron transfer processes mediated by DOM. They synthesized model biochar (Mb) samples with varying conductivity levels by incorporating 0, 10, 20, and 40 mg of graphene into sodium alginate solutions, resulting in samples named Mb-G0, Mb-G10, Mb-G20, and Mb-G40. The mixtures were gelled with calcium chloride (CaCl2), washed, dried, and pyrolyzed at 400 °C under nitrogen (N2). After pyrolysis, DOM was removed to ensure that the observed effects were solely due to the conductivity of biochar.
For the soil incubation experiment, 90 mg of each Mb sample was added to 6 g of paddy soil collected from Jianshui, Yunnan, China. Ethanol (6 mmol) served as the carbon source, and samples were incubated anaerobically at 30 °C.
CH4 and CO2 concentrations were measured over 16 days using gas chromatography. The study then analyzed DOM concentrations using total organic carbon (TOC) analysis, and the composition of DOM was assessed using excitation-emission matrix (EEM) fluorescence spectroscopy.
The electron transfer rate (ETR) was quantified using cyclic voltammetry (CV) with a three-electrode system. Microbial community composition was analyzed through 16S ribonucleic acid (rRNA) sequencing on an Illumina NovaSeq platform. To confirm DOM’s role in electron transfer, experiments used anthraquinone-2,6-disulfonate (AQDS), a quinone analogue representing electroactive DOM, and CV curves were assessed.
Key Outcomes on Methane Production
The study demonstrated a strong link between biochar conductivity and CH4 production in paddy soils. The most conductive biochar, Mb-G40 (0.43 S cm-1), produced 3.45 ± 0.12 mmol CH4, which was 69% higher than the control (2.04 ± 0.06 mmol). Other Mb variants (Mb-G10, Mb-G20) led to 18-26% increases due to faster electron transfer mediated by DOM, rather than changes in the microbial community.
Electrochemical analysis found distinct redox peaks in Mb-treated soils, confirming that DOM played a key role in electron transfer. The ETR in Mb-G40-treated soil reached (7.22 ± 0.61) × 10-4 μmol e- s-1, closely matching the increase in CH4 production (r = 0.85, p < 0.05).
Interestingly, the electron-donating and accepting capacities of biochar decreased with higher graphene content, indicating that conductivity, rather than redox activity, was the main factor boosting ETR. In AQDS experiments, Mb-G40 showed the highest adsorption capacity, supporting its role in enhancing DOM-mediated electron transfer.
Microbial analysis indicated a shift in methanogenic pathways. Acetoclastic methanogens (Methanosaeta, Methanothrix) decreased, while hydrogenotrophic and electron-driven methanogens increased. This suggests a transition from acetate-driven to electron-driven methanogenesis, aligning with the observed increase in CH4 production.
Applications for Sustainable Agriculture
This research has significant implications for sustainable agriculture, particularly in rice cultivation. Farmers could potentially increase CH4 production in paddy soils by enhancing biochar conductivity, supporting bioenergy generation while addressing greenhouse gas emissions. Incorporating graphene into biochar improves conductivity and overall effectiveness, allowing for tailored applications that optimize soil health and nutrient cycling.
Conductive biochar can thus support anaerobic digestion, reduce reliance on chemical fertilizers, and contribute to carbon sequestration. Understanding the underlying electron transfer mechanisms also opens opportunities for broader applications in climate-smart agriculture, bioremediation, microbial fuel cells, and circular bioeconomy models.
Conclusion and Future Directions
The study demonstrates that biochar conductivity plays a crucial role in enhancing CH4 generation in paddy soils by facilitating electron transfer through DOM. It shows that increased CH4 production results from improved electron transfer rather than changes in microbial abundance.
Future work should explore long-term field applications, interactions with different soil types and amendments, and the broader environmental impacts of biochar use. Investigating the scalability of conductive biochar production and its effect on greenhouse gas emissions will be crucial for developing sustainable agricultural strategies. As the demand for climate-smart farm solutions grows, conductive biochar offers a promising way to improve soil health, enhance biogas production, and mitigate greenhouse gas emissions.
Disclaimer: The views expressed here are those of the author expressed in their private capacity and do not necessarily represent the views of AZoM.com Limited T/A AZoNetwork the owner and operator of this website. This disclaimer forms part of the Terms and conditions of use of this website.
Source:
Wu, Y., & et al. (2025). Biochar conductivity enhances methane generation in paddy soil by facilitating electron transfer mediated by dissolved organic matter. Biochar, 7(85). DOI: 10.1007/s42773-025-00478-8, https://link.springer.com/article/10.1007/s42773-025-00478-8