Global meta-analyses showed that biochar application can reduce N₂O emission. However, no relevant review study is available for East Asian countries which are responsible for 70% of gaseous N losses from croplands globally. This review analyzed data of the biochar-induced N₂O mitigation affected by experimental conditions, including experimental types, biochar types and application rates, soil properties, and chemical forms and application rates of N fertilizer for East Asian countries. The magnitude of biochar-induced N₂O mitigation was evaluated by calculating N₂O reduction index (R_index, percentage reduction of N₂O by biochar relative to control). The R_index was further standardized against biochar application rate by calculating R_index per unit of biochar application rate (ton ha⁻¹) (Unit R_index). The R_index averaged across different experimental types (n = 196) was −21.1 ± 2.4%. Incubation and pot experiments showed greater R_index than column and field experiments due to higher biochar application rate and shorter experiment duration. Feedstock type and pyrolysis temperature also affected R_index; either bamboo feedstock or pyrolysis at > 400 °C resulted in a greater R_index. The magnitude of R_index also increased with increasing biochar rate. Soil properties did not affect R_index when evaluated across all experimental types, but there was an indication that biochar decreased N₂O emission more at a lower soil moisture level in field experiments. The magnitude of R_index increased with increasing N fertilizer rate up to 500–600 kg N ha⁻¹, but it decreased thereafter. The Unit R_index averaged across experimental types was −1.2 ± 0.9%, and it was rarely affected by experimental type and conditions but diminished with increasing biochar rate. Our results highlight that since N₂O mitigation by biochar is affected by biochar application rate, R_index needs to be carefully evaluated by standardizing against biochar application rate to suggest the best conditions for biochar usage in East Asia.

全球荟萃分析表明，生物炭的应用可以减少 N ₂ O 排放。然而，东亚国家没有相关的审查研究，这些国家造成全球农田气态氮损失的 70%。该综述分析了受试验条件影响的生物炭诱导N ₂ O 减排数据，包括试验类型、生物炭类型和施用率、土壤性质以及东亚国家氮肥的化学形态和施用率。通过计算 N ₂ O 减少指数（R_指数，生物炭相对于对照的 N ₂ O减少百分比）来评估生物炭引起的 N ₂ O 减缓的幅度。R_指数通过计算针对ř生物炭应用率进一步标准化_索引每生物炭施用率（吨公顷的单位^-1）（单位r_索引）。不同实验类型（n = 196）的平均R_指数为 -21.1 ± 2.4%。由于更高的生物炭施用率和更短的实验持续时间，孵化和盆栽实验显示出比柱子和田间实验更大的 R_指数。原料类型和热解温度也影响R_指数；竹原料或 > 400 °C 的热解导致更大的 R_指数。R_指数的大小也随着 biochar 率的增加而增加。土壤性质不影响 R_指数，但有迹象表明，在田间试验中，生物炭在较低的土壤湿度水平下更多地减少了 N ₂ O 排放。R_指数的大小随着施氮量的增加而增加，直至 500-600 kg N ha ^-1，但此后下降。实验类型的平均单位 R_指数为 -1.2 ± 0.9%，它很少受实验类型和条件的影响，但随着生物炭率的增加而减少。我们的结果强调，由于生物炭对N ₂ O 的缓解受生物炭施用率的影响，R_指数 需要通过标准化生物炭应用率来仔细评估，以提出东亚生物炭使用的最佳条件。