不同施肥处理对土壤活性有机碳和甲烷排放的影响

通过采集田间试验区连续3a施入有机肥的稻田耕层土壤,分析土壤中微生物量碳(MBC)、水溶性有机碳(DOC)、易氧化有机碳(ROC)和可矿化有机碳(readily mineralizable carbon,RMC)等活性有机碳的含量,稻田甲烷(CH_4)的排放通量,探讨施用有机肥的土壤活性有机碳变化及与CH_4排放的关系。研究结果显示:(1)施有机肥对土壤中的活性有机碳均有一定的促进作用。3a不同施肥处理土壤中DOC、ROC、MBC和RMC的平均含量分别为383.6、2501.2、640.4 mg/kg和291.7 mg/kg。3a施猪粪(猪粪+化肥,PM)、鸡粪(鸡粪+化肥,CM)和稻草(稻草+化肥,RS)的DOC的含量分别比化肥(CF)处理增加5.6%、6.7%和19.3%,ROC的含量分别比CF增加6.6%、8.4%和9.8%;MBC含量分别比CF增加5.1%、14.8%和21.5%,RMC增加6.8%、22.0%和33.9%。不同施肥处理的稻田土壤活性有机碳为分蘖期高于成熟期。(2)施肥处理显著增加稻田CH_4排放,CH_4分蘖期的排放通量是成熟期的143倍,3a PM、CM和RS处理的CH_4排放分别比CF处理增加37.0%(P0.05)、92.7%(P0.05)和99.4%(P0.05)。(3)不同施肥处理的DOC、ROC、MBC和RMC含量与CH_4排放通量均存在显著正相关关系,ROC与CH_4排放的相关系数最高,为0.754(P0.01),且4种有机碳间关系密切。稻田分蘖期土壤中的活性有机碳与稻田CH_4排放呈显著正相关关系。(4)综合分析,在4种有机碳中,土壤中ROC和MBC的含量直接影响CH_4排放。

Effects of organic manure application on active soil organic carbon and methane emission in paddy soils

Active soil organic carbon (ASOC) is an important component of soil. It plays a critical role in soil organic carbon turnover processes, which potentially contribute to future climate change. The properties of ASOC and its effects on methane (CH₄) emission from paddy soils remain unclear, and were therefore investigated in the present study. We determined ASOC, including microbial biomass carbon (MBC), dissolved organic carbon (DOC), readily oxidized organic carbon (ROC), and readily mineralizable carbon (RMC), for 3 consecutive years after application of organic fertilizer. The treatments used were as follows: (1) no fertilizer (NF); (2) chemical fertilizer (CF); (3) pig manure +chemical fertilizer (PM); (4) chicken manure + chemical fertilizer (CM); and (5) rice straw + chemical fertilizer (RS). The results demonstrated that (1): ASOC increased upon application of organic manures. The 3-year average content of ASOC in DOC, ROC, MBC, and RMC was 383.6, 2501.2, 640.4, and 291.7 mg/kg, respectively. The content of soil DOC, ROC, MBC, and RMC under different treatments was in the following order: RS>CM>PM>CF>NF. The content of DOC was 5.6%, 6.7%, and 19.3% higher in PM, CM, and RS, respectively, than in CF. The content of ROC increased by 6.6%, 8.4%, and 9.8% with PM, CM, and RS, respectively, over that in the CF treatment. The PM, CM, and RS treatments showed 5.1%, 14.8%, and 21.5% higher MBC contents and 6.8%, 22.0%, and 33.9% higher RMC contents, respectively, than CF treatment. The ASOC content was higher at the tillering stage than at the maturity stage. (2): The CH₄ emissions significantly increased with application of organic manure. The CH₄ emissions under different treatments were in the following order: RS > CM > PM > CF > NF. The CH₄ emission in PM, CM, and RS treatments increased by 37.0% (P < 0.05), 92.7% (P < 0.05), and 99.4% (P < 0.05), respectively, over those in the CF treatment. The CH₄ emission was 142-fold higher at the tillering stage than at the maturity stage. (3): With the increasing duration of application, CH₄ emission at rice tillering stage increased in different treatments. Positive correlations were observed among DOC, ROC, MBC, and RMC in all treatments. DOC, ROC, MBC, and RMC contents were strongly correlated with CH₄ emission, (e.g., the highest correlation coefficient between ROC and CH₄ emission, r=0.754, P < 0.05). The contents in DOC, ROC, MBC, and RMC at the tillering stage had a significant correlation with CH₄ emission, with correlation coefficients of 0.537(P < 0.01), 0.754(P < 0.01), 0.728(P < 0.01), and 0.431(P < 0.01), respectively. However, no significant correlation was observed at the maturity stage. In conclusion, ASOC content showed a close correlation with CH₄ emission, especially ROC and MBC content, which might be directly associated with CH₄ emission. The results of the present study suggest that, among the treatments tested, pig manure is the best organic fertilizer because the soil has lower ROC and MBC contents.Application of pig manure could be an effective measure to improve the quality of the soil, render it suitable for sustainable development, and mitigate CH₄ emissions.