[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 (NO) and methane (CH) 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 biochar (B1), nitrogen fertilizer combined with 40 t ·hm biochar (B2), and no nitrogen fertilizer, as the control (CK). The NO and CH 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 NO emission dynamics during the early rice season are closely related to the mineral nitrogen content of the soil. The NO is emitted at the rice seedling and tillering stages after fertilization. The cumulative NO emission during the early rice season was 0.18-0.76 kg ·hm. Compared with the CON treatment, the biochar treatments reduced NO by 18%-43%, and the B2 treatment resulted in a significant reduction. The addition of biochar may promote the reduction of NO at the early rice seedling stage and increase NO emissions by improving the soil NO-N content at the early rice tillering stage. During the late rice season, NO is emitted during the heading and maturity stages, and the cumulative NO emission was 0.17-0.34 kg ·hm. The B1 treatment reduced emissions by 37%, and B2 increased emission by only 3%, which is not a significant difference. The peak of CH 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 CH in the early rice season was 3.11-14.87 kg ·hm. Compared with CON, the CK treatment increased emission by 39%. The biochar treatment may increase soil aeration and limit the ability of CH production in the early rice season, as B1 and B2 treatments reduced CH emissions by 28% and 71%. The cumulative CH emission in late rice season was 53.1-146.3 kg ·hm, and the emission dynamics were significantly positively correlated with NH-N content. CK and B1 treatments increased CH emissions by 52% and 99%, respectively compared with CON, and the B2 treatment significantly increased CH 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.