| Worldwide, more attention has been focused on global warming and the extreme weather events. Global climate change is considered as a result of greenhouse gases (GHGs) emissions, and GHGs emissions become as an important issue of political diplomacy. As one of the largest countries with a huge amount of CO2 emissions, China should play a leader role in rescuing the deteriorating environment. Paddy field ecosystem played an important role in ensuring food security and a great source of GHG (CO2, CH4, N2O) emissions as well. GHGs emissions from paddy fields are mainly affected by cropping rotation system, straw incorporation and N fertilization. In the current study, static opaque chamber-gas chromatograph method was employed to measure CO2, CH4 and N2O emissions simultaneously from two typical different rotation systems in South China.A field study was conducted from November,2008 to June,2010, containing two different rotation systems, i.e. double rice-oilseed rape and single rice-wheat cropping system. Four treatments were performed for each cropping system including control (ck), nitrogen fertilizer without straw incorporation (SO), nitrogen fertilizer with low level straw incorporation (S1) and nitrogen fertilizer with high straw incorporation (S2),. A fallow plot was also included for comparison.In the 2009-2010 annual flooding-drainage rotation, the global warming potentials (GWPs) of CH4 and N2O emissions from each treatment of double rice-oil rape rotation were higher than that from the corresponding treatment of single rice-wheat rotation, among which, CH4 contributed to 61.3% and 96.9% of GWPs. N fertilizer application promoted crop productions significantly, but induced different N2O emission factors between two rotation systems. In rice growing season, N fertilizations with straw amendment have higher greenhouse gas intensity (GHGI) than only N fertilizer treatments, suggesting that apply N fertilization without straw amendment in rice growing season could be effective management in paddy field in mitigation GHGs. There was no significant difference in grain yields among N treatments in each rotation, with higher yields from double rice system than that of single rice system, without obvious difference in GHGI, indicating that double rice cropping rotation be effective management in mitigating GHGs without reduction in yields.During the 2009-2010 annual flooding-drainage rotation paddy ecosystems, CH4 emissions mainly occurred during flooded rice growing season, accounting for more than 90% of annual cumulative emission from paddy fields. In contrast, N2O emissions mainly occurred during the off-rice season and drainage period. N2O emission peaks occurred during drainage period was dependent on the weather condition. Higher cumulative CH4 emission and emission intensity during the late rice growing season indicated a stronger potential for mitigating CH4 emissions from double rice paddy field. N2O emissions were mainly induced by N fertilization, indicating the importance of improving nitrogen use efficiency in mitigating N2O emission from paddy fields. Different rotation systems produced significant effect on CH4 and N2O emissions. Straw incorporation significantly enhanced CH4 emission while N fertilization significantly promoted N2O emission.During the 2009-2010 annual flooding-drainage rotations, N application significantly promoted ecosystem CO2 emission, while straw amendments didn't make difference. Treatments in double rice-oilseed rape rotation system produced higher CO2 emissions than the corresponding treatment in single rice-wheat rotation system.Analysis and comparison of GHGs emissions from paddy field during 2008-2009 and 2009-2010 winter drained crop growing seasons showed that N2O and CO2 have great inter-annual variations. N2O emissions were mainly depended on water condition in previons crop growing season, precipitation, N fertilization and crop growth while CO2 emissions were mainly depended on crop growing status and weather condition. N2O emissions were significantly influenced by N fertilization and soil moisture during 2008-2009 crop growing season, while cumulative N2O emissions mainly depended on corp growth duration without significant difference in N2O flux for different crops. N2O emissions from plots without N fertilization were slightly lower than that from fallow plot, suggesting that crop cultivation could reduce N2O emissions during winter drained crop growing season. |
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