| Atmospheric concentrations of greenhouse gases (CH4, CO2and N2O) increased dramatically in recent decades, which are of concern due to their contributions to global warming. Thus, the research on greenhouse gases mitigation by agricultural management is becoming a hotspot. Winter flooded paddy field is widely distributed in southwestern China. However, to our knowledge, we failed to find research on mitigation of flooded paddy, though this kind of paddy has the potential of greenhouse gases mitigation. Therefore, we chose typical winter flooded paddy in Central Sichuan hilly area to investigate the effect of altering rice-flooded-fallow paddy (RF) to rice-wheat rotation (RW) on the emissions of greenhouse gases, and to provide reference for the greenhouse gases mitigation research.Field experiments were conducted in Yanting station (Chinese Academy of Sciences) from August30,2012to August30,2013. We measured fluxes of CH4, CO2and N2O from different treatments by the static opaque chamber and gas chromatography techniques, and estimated their global warming potentials (GWP). In order to analyze the relationship between gas fluxes and environmental factors, at the same time of gas sampling, soil moisture and temperature were recorded; we also collected soil samples to measure dissolved nitrogen and carbon concentration. The results are as follows:1. RF and RW showed obvious seasonal patterns in CH4and CO2fluxes:high in autumn and summer, while low in spring and winter season. N2O flux peaked following nitrogen fertilization in wheat season, but we did not observe high N2O flux after fertilization in flooded rice season. The decrease of water content tended to lead to pulse emission of N2O. Average fluxes of CH4, CO2(ecosystem respiration) and N2O from RF were4.35,133.92mg C m-2h-1and6.08μg N m-2h-1respectively, the corresponding fluxes for RW were2.56,173.04mg C m-2h-1and49.92μg N m-2h-1respectively. The conversion from RF to RW increased N2O flux and decreased CH4flux.2. N2O-N emission factor for RF and RW were0.14%and0.60%, the difference between them was resulting from nitrogen fertilizer application in the wheat season. Emission factor for RW was1.22%in the wheat season and the values in flooded rice season were very small for both RW and RF.3. GWPs for RF, RW were-3016.21and-14472.02kg CO2-eq ha-1yr-1, respectively. Carbon sequestration by photosynthesis offset the global warming effect of CH4and N2O, made them the sink of atmospheric CO2-eq. Although two treatments showed negative effect to global warming, but RW gained more CO2-eq benefits.4. Soil temperature and water content had important effect on gas fluxes. Soil temperature correlated significantly to CH4, CO2fluxes. Water depth during flooded period correlated extremely significant to CO2flux (p <0.01). There was a positive linear correlation between soil volumetric water content and N2O, CO2fluxes in non-flooded season.5. Dissolved organic carbon, dissolved total nitrogen, dissolved organic nitrogen and mineral nitrogen affected greenhouse gases fluxes with different magnitude. The relationship between N2O fluxes and soil mineral nitrogen or dissolved total nitrogen were significant (r were0.54,0.25respectively, p <0.01). Dissolved organic carbon and nitrogen were in significant negative relationship to CH4and CO2fluxes.6. Plants increased CH4and respiratory CO2fluxes when compared to no vegetation treatments, which was more remarkable in rice season than wheat season for CH4fluxes. As for CO2fluxes, the influence of plant were obvious in both rice and wheat season.7. At the first year of conversion, changes in soil organic carbon and total nitrogen were not obvious (p>0.05). The flooded paddy tended to increase soil organic carbon and total nitrogen, indicating that the conversion may decrease soil carbon and nitrogen.In a word, transforming winter-flooded paddy to rice-wheat rotation decreased global warming impact of greenhouse gases and increased carbon benefits as well as grain yields, which is beneficial to the environment and the farmer. |
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