不同灌溉模式和施氮量条件下稻田甲烷排放及其与有机碳组分关系

通过田间试验,研究不同灌溉模式和施氮量下早晚稻不同生育期土壤有机碳(SOC)和易氧化有机碳(LOC)含量、微生物量碳(MBC)和甲烷氧化菌(MOB)数量的变化,以及水稻生育期内稻田甲烷排放通量变化情况,并分析当日稻田甲烷排放通量与土壤SOC、LOC、MBC和MOB的关系,以期获得稻田甲烷减排的灌溉模式和施氮量。两季试验均设3种灌溉模式,即常规灌溉(C)、"薄浅湿晒"灌溉(T)和干湿交替灌溉(D);2种施氮量,即120 kg·hm~(-2)(N1)和150 kg·hm~(-2)(N2)。结果表明,N1时D模式土壤SOC含量在晚稻乳熟期和早稻孕穗期较高,N2时早、晚稻4个时期SOC含量均以D模式最高;早晚稻土壤LOC含量以D模式较低,土壤MOB数量均以C模式较低,而MBC则以C模式较高。N2处理稻田MOB、SOC、LOC和MBC含量均高于N1处理。稻田甲烷排放量在分蘖期和乳熟期较高,而在孕穗期和成熟期较低。D模式早、晚稻全生育期甲烷排放通量和累计排放量均显著低于T和C模式,而N2处理这些指标均高于N1。稻田甲烷排放通量受土壤MOB、LOC和MBC的直接影响和SOC含量的间接影响,在干湿交替模式和施氮量120 kg·hm~(-2)下稻田甲烷排放量最低。

Soil CH4 emission and its relationship with organic carbon fraction under different irrigation methods and nitrogen rates

The readily decomposed organic matter in the paddy ecosystem increase soil methane(CH4)emission under anaerobic environ-ment, while methane oxidizing bacteria(MOB)oxidation of methane reduces soil CH4 emission under better aeration environment. Field ex-periments with different irrigation methods and nitrogen(N)rates were carried out to measure the contents of organic carbon(SOC)and eas-ily oxidized organic carbon(LOC), microbial biomass carbon(MBC)and the number of MOB at different growth stages, and CH4 emission fluxes from paddy field during the growth stage, and then the relationships between the CH4 emission flux and the contents of SOC and LOC, MBC and MOB in soils at the sampling days were analyzed, so as to obtain the rational irrigation mode and N rate for CH4 reduction. Two-season field experiments included three irrigation methods, i.e. conventional irrigation(C),"thin-shallow-wet-dry"irrigation(T)and alter-nate drying and wetting irrigation(D), and two N rates(N1120 kg·hm-2 and N2150 kg·hm-2). Results show that D mode had lower SOC content at the booting stage of late rice and tillering stage of early rice under N1, and D mode had the highest SOC content at the four growth stages of early rice and late rice under N2. When planting early rice and late rice, D mode had lower LOC content, and C mode had lower MOB and higher MBC. The contents of SOC, LOC, MBC and MOB in N2 were higher than those of N1. Accumulative CH4 emissions over the whole growth stage of early rice or late rice and the total of both seasons in D mode were significantly lower than those of T and C modes, but these indices in N2 were higher than those of N1. CH4 emission flux was directly influenced by the soil MOB, LOC and MBC and indirectly affected by the SOC. CH4 emission from paddy soil was the lowest under alternate drying and wetting irrigation and N rate of 120 kg·hm-2.