Abstract:

Replacing chemical fertilizers with organic fertilizers from livestock and poultry manure is an important measure to reduce fertilizer application and recycle nutrients. A field experiment was conducted to study the effects of the combined application of cow manure and chemical fertilizers on CH₄ and N₂O emissions and related factors in a double-rice cropping system in Hunan Province. Gas fluxes were measured using the static chamber/gas chromatography method, and the dynamics of the soil chemical, physical, and biological properties were determined. The findings showed that compared to traditional fertilizer application, the combined application of manure had a significant impact on cumulative CH₄ and N₂O emissions. Specifically, throughout the two rice-growing seasons, the total CH₄ emissions of 50% chemical nitrogen fertilizer replaced with cow dung (CM) increased dramatically by 43.2% compared with the conventional nitrogen fertilizer (CON) treatment. When comparing the CM and CON treatments, the cumulative N₂O emissions were reduced by 45.2%. Soil pH, ammonium nitrogen, nitrate nitrogen, organic carbon, total nitrogen, and soluble organic carbon were all significantly improved by the CM treatment; however, soil Eh was significantly decreased. Owing to changes in soil properties, the mean copy numbers of genes that produce and oxidize methane increased by 79.1% and 13.0% in the early and late rice seasons, respectively. There was a significant increase of 35.8%, 50.8%, and 7.1% in the average gene copy numbers of the fully ammonia-oxidizing amoA, denitrifying nirS, and denitrifying nosZ functional genes, respectively. In contrast, the gene copy numbers of the functional genes nosZⅡ and nirK decreased by 17.5% and 46.5%, respectively. Redundancy analysis revealed that the average emission flux of CH₄, copy number of the gene that produces methane, and copy number of the gene that oxidizes methane were most influenced by soil organic carbon and soil total nitrogen content. In addition, soil organic carbon, soil ammonium nitrogen, and soil total nitrogen had significant impacts on the average emission flux of N₂O, copy numbers of completely ammonia-oxidizing amoA functional genes, denitrifying nirS functional genes, denitrifying nosZ functional genes, denitrifying nirK functional genes, and denitrifying nosZⅡ functional genes of bacteria. Considering the total greenhouse effect of CH₄ and N₂O emissions, greenhouse gas emissions (in CO₂ terms) from the CM treatment significantly increased by 41.0% compared to the CON treatment. In conclusion, the combined application of organic and inorganic fertilizers in paddy fields changes the physicochemical and biological properties of the soil and increases greenhouse gas emissions, which should be considered when assessing the greenhouse effects in paddy fields.

Key words: paddy field, cow manure, methane, nitrous oxide, soil microbe

摘要：

畜禽粪便有机肥替代化肥是实现农田化肥减施和养分循环利用的重要措施。以湖南典型红壤双季稻田系统为研究对象，采用静态箱-气相色谱法结合土壤理化和生物学性质测定，研究了水稻生长季基肥配施牛粪条件下CH₄和N₂O的排放特征及其主要影响因素。结果表明，与常规施用化肥处理相比，牛粪化肥配施显著影响CH₄和N₂O累积排放量。具体而言，两个稻季生长期内牛粪替代50%化学氮肥处理（CM）的CH₄累积排放量较常规氮肥处理（CON）显著提高43.2%；而CM处理N₂O累积排放量较CON处理显著降低45.2%。同时CM处理显著增加了土壤有机碳、土壤总氮、土壤可溶性有机碳、土壤铵态氮和硝态氮质量分数和土壤pH，但显著降低了土壤Eh。受土壤性质改变的影响，早晚稻季土壤中甲烷产生功能基因、甲烷氧化功能基因的基因拷贝数平均分别显著增加79.1%、13.0%；同时完全氨氧化细菌amoA功能基因、反硝化nirS功能基因、反硝化nosZ功能基因的基因拷贝数平均分别显著增加35.8%、50.8%、7.1%，但反硝化nirK功能基因和反硝化nosZⅡ功能基因的基因拷贝数平均分别显著降低了46.5%和17.5%。通过冗余分析发现，土壤有机碳和土壤总氮质量分数对CH₄平均排放通量、甲烷产生功能基因拷贝数、甲烷氧化功能基因拷贝数的影响作用最大。另外土壤有机碳、土壤铵态氮和土壤总氮质量分数对N₂O平均排放通量、完全氨氧化细菌amoA功能基因拷贝数、反硝化nirS功能基因拷贝数、反硝化nosZ功能基因拷贝数、反硝化nirK功能基因和反硝化nosZⅡ功能基因的基因拷贝数的影响作用最大。考虑CH₄和N₂O的总的温室效应，与CON处理相比CM处理的温室气体排放（以CO₂计）显著增加了41.0%。综上所述，稻田有机无机肥配施改变土壤理化和生物学性质而增加了温室气体排放，需要在稻田温室效应评估中加以考虑。

关键词: 稻田, 牛粪, 甲烷, 氧化亚氮, 土壤微生物