椰糠生物炭对热区双季稻田N2O和CH4排放的影响

基于稻菜轮作模式，选择海南双季稻田为对象进行氧化亚氮（N₂O）和甲烷（CH₄）排放的原位监测，探究椰糠生物炭对该系统稻田温室气体排放的影响.试验设当地常规施肥对照（CON）、氮肥配施20 t·hm^-2生物炭（B1）、氮肥配施40 t·hm^-2生物炭（B2）及不施氮对照（CK）4个处理，采用静态箱-气相色谱法监测整个水稻种植季稻田N₂O和CH₄排放，并估算增温潜势（GWP）和温室气体排放强度（GHGI）.结果表明，早稻季N₂O排放动态与土壤矿质氮含量密切相关，排放集中在水稻苗期与分蘖期施肥后，各处理早稻季N₂O累积排放量为0.18~0.76 kg·hm^-2，相较于CON处理，生物炭处理减排18%~43%，其中B2处理达显著水平；生物炭可能通过促进N₂O的还原减少早稻苗期N₂O排放；提高土壤硝态氮含量而增加了早稻分蘖期N₂O排放.晚稻季N₂O排放集中在抽穗期和成熟期，累积排放量为0.17~0.34 kg·hm^-2，B1处理减排37%，B2增加3%，差异均不显著.稻田CH₄排放高峰出现在早稻季后期与晚稻季前期.各处理早稻季CH₄累积排放量为3.11~14.87 kg·hm^-2，CK较CON处理增排39%，生物炭处理可能提高土壤通气性限制早稻季产CH₄能力，B1和B2处理分别较CON减排28%和71%；晚稻季CH₄累积排放量为53.1~146.3 kg·hm^-2，排放动态与NH₄⁺-N含量极显著正相关，CK和B1分别较CON处理增加52%和99%，B2处理显著增加176% CH₄排放.早稻季B1和B2处理较CON分别增产12.0%和14.3%，晚稻季分别增产7.6%和0.4%.由于晚稻季甲烷排放的增加，施用生物炭增加了双季稻田总增温潜势（GWP），其中高量生物炭达显著水平；不同施用量生物炭对双季稻田温室气体排放强度（GHGI）无显著影响.椰糠生物炭在热区稻田温室气体减排方面的应用仍需进一步研究.

Effects of Coconut Chaff Biochar Amendment on Methane and Nitrous Oxide Emissions from Paddy Fields in Hot Areas

Based on the rice-vegetable crop rotation model, in-situ measurements of nitrous oxide (N₂O) and methane (CH₄) emissions were conducted in double-cropping rice fields in Hainan to determine the impact of coconut chaff biochar on greenhouse gas emissions. The experiment involved four treatments:conventional farming fertilization (CON), nitrogen fertilizer combined with 20 t ·hm^-2 biochar (B1), nitrogen fertilizer combined with 40 t ·hm^-2 biochar (B2), and no nitrogen fertilizer, as the control (CK). The N₂O and CH₄ emissions were measured using static chamber-gas chromatography during the two paddy seasons, and the global warming potential (GWP) and greenhouse gas intensity (GHGI) were also estimated. The results show that N₂O emission dynamics during the early rice season are closely related to the mineral nitrogen content of the soil. The N₂O is emitted at the rice seedling and tillering stages after fertilization. The cumulative N₂O emission during the early rice season was 0.18-0.76 kg ·hm^-2. Compared with the CON treatment, the biochar treatments reduced N₂O by 18%-43%, and the B2 treatment resulted in a significant reduction. The addition of biochar may promote the reduction of N₂O at the early rice seedling stage and increase N₂O emissions by improving the soil NO₃^--N content at the early rice tillering stage. During the late rice season, N₂O is emitted during the heading and maturity stages, and the cumulative N₂O emission was 0.17-0.34 kg ·hm^-2. The B1 treatment reduced emissions by 37%, and B2 increased emission by only 3%, which is not a significant difference. The peak of CH₄ emissions from rice fields appeared in the late phase of the early rice season and prophase of the late rice season. The cumulative emission of CH₄ in the early rice season was 3.11-14.87 kg ·hm^-2. Compared with CON, the CK treatment increased emission by 39%. The biochar treatment may increase soil aeration and limit the ability of CH₄ production in the early rice season, as B1 and B2 treatments reduced CH₄ emissions by 28% and 71%. The cumulative CH₄ emission in late rice season was 53.1-146.3 kg ·hm^-2, and the emission dynamics were significantly positively correlated with NH₄⁺-N content. CK and B1 treatments increased CH₄ emissions by 52% and 99%, respectively compared with CON, and the B2 treatment significantly increased CH₄ emissions by 176%. Compared with CON, the B1 and B2 treatments increased the yield by 12.0% and 14.3% when applied in the early rice season and by 7.6% and 0.4% when applied in the late rice season, respectively. Due to the increased methane emissions in the late rice season, biochar amendment increased the GWP of the double-cropping rice field, in which the high amount of biochar reached a significant level; different amounts of biochar had no significant effect on the GHGI of the double-cropping rice field. Thus, the application of coconut chaff biochar for the reduction of greenhouse gas emission, from rice fields in hot areas, requires further research.