Biochar emerged as a potential solution to mitigating greenhouse gas emissions, though previous studies obtained variable results regarding its effects on methane (CH₄) emissions and crop yields. Global meta-analyses were conducted regarding the effectiveness of biochar, though regional meta-analyses are still needed. We performed a meta-analysis of 43 published papers to obtain the central tendency of the response to biochar application in East Asian rice paddies. Biochar application significantly reduced methane emissions while increasing the soil organic carbon (SOC) content and crop yield. We identified the most significant influencing factors on the CH₄ emissions, SOC content, and crop yield. Our findings provide a scientific basis for the application of biochar to East Asian rice paddies, as well as to study the effects of biochar application in East Asian rice paddies. The numbers in parentheses represent the sample sizes.

Biochar application has been considered as a promising solution to address the effects of modern agriculture on climate change. However, there is a lack of research on the biochar application of greenhouse gas emissions based on poor soils in Korean agricultural land. Therefore, this study aimed to evaluate the effects of biochar application according to different soil characteristics on soil organic carbon (SOC) improvement and greenhouse gas reduction. The incubation experiments were conducted for 49 days and used different feedstock (barley straw and poultry manure) and biochar application rates (0, 5, 10, and 20-ton ha⁻¹) in four soil characteristics (upland, U; greenhouse, G; converted land, C; reclaimed land, R). The results of this study showed that the SOC increased significantly in all soils after biochar application. The increasing SOC rate was the highest in poor soil. Biochar 20-ton ha⁻¹ treatment significantly reduced N₂O emissions by 33.2% compared with the control. Barley straw biochar significantly reduced N₂O emissions from all soils. Barley straw biochar decreased approximately 74.5% of N₂O emissions compared with poultry manure biochar. Poultry manure biochar improved SOC and reduced N₂O emissions in poor soil. However, in poultry manure biochar treatment in U and G soil, N₂O emissions increased. In conclusion, barley straw biochar application was found to suppress N₂O emissions and improve the SOC in all soil characteristics of agricultural land. In addition, the soil carbon storage effect and N₂O reduction effect of biochar were the highest in poor soil. Thus, the biochar application can be a potential agricultural practice for improving soil quality and decreasing N₂O emissions in domestic agricultural soil.

우리나라에서 배출되는 메탄의 22%는 벼를 재배하는 논에서 발생하고 있다. 이와 관련하여 국내에서도 논에서 배출되는 메탄에 대하여 다양한 연구를 수행해 왔다. 그러나 연구 사례에 대해 전반적으로 정리된 바가 없어 연구 현황 및 필요한 연구 부분에 대한 파악이 어렵다. 본 리뷰에서는 국내에서 실시한 논에서의 메탄 관련 연구 사례에 대한 정리를 통해 앞으로 필요한 연구 부분에 대한 방향성을 제시하고자 하였다. 동시에 논이라는 특이적 환경에서 메탄 배출에 대한 이해를 돕기 위해 관련 배경 지식에 대한 정보도 함께 제공하고자 하였다. 물을 가둔 논은 혐기적 환경이 발달하여 산화환원전위가 음의 값을 나타내며, -100 ~ -200 mV에 이르면 메탄생성균의 활성이 촉진되어 메탄이 배출된다. 또한 균의 최적 조건인 토양 온도 20 ~ 40℃에서 유기물의 분해산물인 아세트산과 수소/이산화탄소와 같은 기질이 공급되면 메탄 배출이 더욱 가속화된다. 이후, 토양 내에서 발생한 메탄의 80 ~ 90%는 식물체 기공을 통해, 그 외 일부는 분출 및 확산 과정을 통해 대기 중으로 방출된다. 그동안 국내에서는 메탄생성균의 활성에 영향을 주는 여러 영농활동 별 메탄 배출에 관한 연구가 이루어져 왔다. 상당수의 연구들이 메탄 배출 증감과 관련하여 논물 및 유기물 관리에 초점을 두고 수행되었다. 그 외에도 토양 관리, 식물체(벼 품종), 메탄 배출 저해제 영향 등에 대한 메탄 배출량이 조사된 바 있다. 그러나 대부분의 연구들은 단기적인 메탄 배출량 평가 위주로 수행된 것들로 장기적인 영농활동에 의한 메탄 배출 영향에 대한 조사는 다소 미흡했다. 또한 메탄 발생량에 한정된 결과 중심으로 조사되어 메탄 배출에 영향을 미치는 인자에 대한 세부적인 분석이 다소 부족하기도 했다. 따라서 앞으로의 연구는 장기적인 토양 관리 등에 의해 변화하는 메탄배출을 포함하여 메탄 배출에 영향을 미치는 각각의 요인에 대한 세부적 연구가 필요할 것으로 판단된다. 이로부터 얻는 연구 결과를 활용하여 차후 전략적으로 메탄 배출을 줄이는 방법에 대한 구체적 방안 제시를 통해 국가 메탄 배출 저감에 기여할 수 있을 것이다.

Methane emissions from flooded rice paddies are a major source of atmospheric methane and represent a significant greenhouse gas with high climate-forcing potential due to anthropogenic activities globally. For sustainable agriculture, it is necessary to find effective methods for mitigating greenhouse gas emissions without reducing crop productivity. We investigated mechanisms to reduce methane emissions during rice cultivation by applying rice straw, rice husk biochar, humic acid, and a humic acid–iron complex, assessing greenhouse gases and rice yield over a single season. The results demonstrated that the treatment plots with rice straw and the humic acid–iron complex significantly reduced methane emissions (563 ± 113.9 kg ha⁻¹) by 34.4% compared to plots treated with rice straw alone (859 ± 126.4 kg ha⁻¹). Rice yield was not compromised compared to the control group treated with only NPK fertilizer, and growth in terms of plant height and tiller number was enhanced in the plots treated with rice straw and the humic acid–iron complex. Conversely, the plots treated solely with rice husk biochar and humic acid did not show a methane reduction effect when compared to the NPK treatment. The humic acid–iron complex has demonstrated potential as a methane mitigation agent with practical applicability in the field, warranting further long-term studies to validate its effectiveness.

Paddy fields are considered one of the most important sources of anthropogenic methane (CH 4) emissions. Drainage of the flooded soils can reduce CH 4 substantially, but rice yields can be variable depending on soil drainage. Therefore, to reduce this variability, water management effects on CH 4 emissions and rice yields were comprehensively analyzed in paddy fields of countries similar to Korea. Here, we selected 161 observations of water management and 174 observations of rice yields from 28 articles and conducted a regional-scale meta-analysis of the effects of water management practices on CH 4 emissions and rice yields in paddy fields. As a result of the analysis, we found that water management practices in East Asian paddy fields reduced methane by 60.5%. Water management practices in paddy fields decreased rice yield by 5.8% but there was no significant. The water management practices of the paddy fields with a high CH 4 emission reduction effect and no impact on rice yields were alternating wet and dry (AWD), flooding-drainage-reflooding (FDF), and moist irrigation (MI) practices. Therefore, it is considered that the above three practices can be applied in Korea. The results of this study are expected to predict CH 4 emissions and rice yields generated by water management practices in East Asian rice paddies in the future and be used as basic data for the development of national unique coefficients.