Reducing greenhouse gas emissions from rice cultivation applied with melaleuca and rice husk biochar in the Vietnamese Mekong Delta

ABSTRACT

Biochar application is considered a potential approach to mitigating greenhouse gas emissions (GHGs) from the agricultural sector and improving soil physicochemical properties. Thus, we conducted a field experiment to examine the efficacy of biochar application rates in combination with water management practices on soil methane (CH₄) and nitrous oxide (N₂O) emissions and carbon increment in the Vietnamese Mekong Delta (VMD). Rice husk biochar (RB) and Melaleuca biochar (MB) were incorporated in the topsoil (0–20 cm) at 5 and 10 Mg ha⁻¹, followed by the water management regimes of continuous flooding (CF) and an alternative wetting and drying (AWD). The results identified that biochar application rates and water management measures were major factors in decreasing CH₄ and N₂O emissions. Compared with the conventional practice, the RB and MB amendment in the rice fields under CF practices reduced 12.9–21.3% of total GHGs (tGHGs), while biochar incorporation under the AWD management practice reduced from 22.3% to 30.5% tGHGs. Compared to CF treatments, biochar amendment concerning the AWD regime lowered from 25.4% to 31.6% tGHGs. Increasing biochar from 5 to 10 Mg ha⁻¹ did not reduce tGHGs considerably. We identified that biochar application significantly increased grain yields from 12.8% to 20.6% under the CF management practice, while the percentage varied from 2.5% to 3.8% for the AWD practice. Similarly, higher grain yields were achieved from 4.9% to 13.7% by applying AWD compared to the CF treatments. Our findings showed that although higher biochar application rates could reduce the tGHGs, the difference in biochar types and water management applications in connection with the tGHGs was neglectable. Incorporating biochar enhanced soil bulk density and porosity under AWD and CF practices. Going forward in further studies, we recommend a long-term biochar application in the VMD’s low-lying paddy fields with a broader range of biochar rates under different soil types.

KEY WORDS:

• Alternative wetting and drying
• continuous flooding
• greenhouse gas emissions
• melaleuca biochar
• rice husk biochar

Acknowledgments

We would like to thank Mr. Ho Minh Nhut (master student, K25, Can Tho University, Vietnam) for supporting this study. We also thank the Laboratory of Environmental Toxicology at Can Tho University for supporting the analysis. We thank Dr. Nigel Downes for proofreading the manuscript.

Disclosure statement

No potential conflict of interest was reported by the author(s).

Supplemental material

Supplemental data for this article can be accessed online at https://doi.org/10.1080/00380768.2024.2324823

Additional information

Funding

This study is funded in part by the Can Tho University Improvement Project VN14-P6, supported by a Japanese ODA loan.