Effects Of Sulfur-containing Industrial By-products On Greenhouse Gases Emissions From Yellow Paddy Fields

Paddy fields are important sources of man-made emissions of the greenhouse gases methane?CH₄?,carbon dioxide?CO₂?and nitrous oxide?N₂O?.China is a large country for rice cultivation,and its cultivation area and rice production account for 19%and28%of the global rice cultivation area and rice production,respectively.Therefore,it is of great importance to carry out researches on greenhouse gas emission patterns and emission reduction measures in rice fields for global greenhouse gas emission reduction.China's fuel combustion is still dominated by coal combustion.With the development of the flue gas desulfurization process,there are more and more sulfur-containing industrial by-products—flue gas desulphurized gypsum?FGDG?—produced in coal-fired power plants.The main component of FGDG is CaSO₄·2H₂O.After applied FGDG to paddy fields,it can provide a large amount of sulfate(SO₄^2-)and enhance the competition of sulfate-reducing bacterias for hydrogen,acetic acid and other substrates,thereby inhibiting the activity of methane-producing bacterias and then reducing CH₄ production.But it can increase the emissions of CO₂ at the sanme time.In addition,FGDG is rich in nutrients that may affect the growth and metabolism of nitrification and denitrifying bacterias,which can indirectly affects the emissions of N₂O.At present,the application of sulfur-containing industrial by-products in agriculture is still in the research stage,mainly focused on soil improvement,crop yield increase,soil phosphorus loss and heavy metal pollution,etc.There are few researches on farmland greenhouse gases emissions,and the study that simultaneously observe three greenhouse gases?CH₄,CO₂,and N₂O?is even rarer.Therefore,select the typical yellow paddy field in Chongqing as the research object and observe the CH₄,CO₂ and N₂O emission fluxes during the rice-growing season and leisure period by using static chamber-gas chromatography technique.Compare and analyze the CH₄,CO₂ and N₂O emissions from paddy field at different level of FGDG(the amount of FGDG applied for CK,T1,T2,T3 and T4 are 0,2,4,8 and 16 t·hm^-2respectively).Evaluate the net carbon budget and greenhouse gas revenue and expenditure in paddy ecosystems.Finally,put forwad the suggestion about greenhouse gas emission reduction and resource utilization of FGDG.The main findings are as follows:1.The seasonal dynamics of CH₄ emission from paddy fieldDuring the rice-growing season,the CH₄ average emission flux of CK?the control treatment?was 25.72±3.61 mgC·m^-2·h^-1.After applying FGDG,the average emission flux significantly decreased by 30.00%to 82.28%?P<0.05?.During the leisure period,the CH₄ average emission flux of CK was 108.39±10.40?gC·m^-2·h^-1.Compared with CK,there was no significant change in T1 and T4,but T2 and T3 increased by 75.39%and 167.59%,respectively.2.The cumulative CH₄ emission from paddy soilDuring the rice-growing season,the accumulated CH₄ emissions of CK was692.98 kgC·hm^-2.The application of FGDG resulted in an exponential decline in cumulative CH₄ emissions from paddy fields,which was 112.48⁴82.61 kgC·hm^-2.During the leisure period,there was no significant relationship between CH₄ emissions and the amount of FGDG.And the accumulated CH₄ emission of CK and FGDG treatments were 18.46 and 6.90³3.89 kgC·hm^-2,respectively.CH₄ emissions mainly occured in rice-growing season and its emissions can reach 89.95%to 99.27%of the total emissions during the entire monitoring period.3.The seasonal dynamic of CO₂ emission from paddy fieldDuring the rice-growing season,the CO₂ average emission flux of CK was33.61±8.71 mgC·m^-2·h^-1.Adding FGDG had no significant effect on CO₂ emissions and the average emission fluxes was 27.15±2.75 to 33.76±5.00 mgC·m^-2·h^-1.During the leisure period,the CO₂ average emission flux of CK was 31.70±3.63 mgC·m-²·h^-1,whcih was not significant different from the FGDG treatments(26.13±4.07 to34.79±6.52 mgC·m^-2·h^-1).4.The cumulative CO₂ emission from paddy soilThe cumulative CO₂ emissions of CK during the rice-growing season and leisure period were 914.63 and 2082.79 kgC·hm^-2,respectively.The application of FGDG had no significant effect on the CO₂ emission during the rice-growing season(734.61⁹36.20 kgC·hm^-2)and leisure period(1796.46²233.20 kgC·hm^-2)?P>0.05?.CO₂ emissions were mainly concentrated in the leisure period,accounting for 67.96%to74.15%of the total emissions during the entire monitoring period.5.The seasonal dynamic of N₂O emission from paddy fieldDuring the rice-growing period,the N₂O average emission flux of CK was5.07±1.54?gN·m^-2·h^-1.The application of FGDG significantly reduced the N₂O emission?P<0.05?,and its average flux was-7.11±1.40 to-1.04±0.16?gN·m^-2·h^-1.During the leisure period,the average emission flux of CK was 49.20±7.69?gN·m^-2·h^-1.After adding FGDG,there was no significant change in the N₂O emissions of T1(49.06±4.64?gN·m^-2·h^-1)and T2(47.51±9.35?gN·m^-2·h^-1)?P>0.05?.But it made the average emission flux of T3 and T4 decreased to 1.53±1.09 and 1.94±1.13?gN·m^-2·h^-1,respectively?P<0.05?.6.The cumulative N₂O emission from paddy soilDuring the rice-growing season,the cumulative N₂O emission of CK was 0.123kgN·hm^-2.Applying FGDG made the cumulative emission dropped to-0.260 to-0.046kgN·hm^-2?P<0.05?.During the leisure period,the cumulative emission of CK was3.137 kgN·hm^-2.After adding FGDG,there was no significant change in T1 and T2,and their cunulative enmissions were 3.059 and 2.846 kgN·hm^-2,respectively.But the cumulative emission of T3 and T4 clearly reduced to 0.326 and 0.026 kgN·hm^-2?P<0.05?,respectively.The N₂O emission from rice fields were mainly concentrated in the leisure period.7.Greenhouse gas budget in paddy fieldsDuring the rice-growing season,compared with CK,the application of FGDG contributed to the accumulation of carbon in paddy field ecosystems and its NECB increased by 2.05%to 74.56%.At the same time,it also weakened the net warming effect of greenhouse gases and made the NGWP reduce by 48.51%to 167.84%.During the leisure period,FGDG had no significant effect on the net carbon balance and the net warming effect of greenhouse gases in the paddy ecosystem.As for the entire monitoring period,the NGWP of CK was 24.92 tCO₂-eq hm^-2,which represented the source of greenhouse gases.After applying FGDG,its NGWP was significantly reduced by 35.53%to 108.68%.Among them,T1,T2 and T3 still appeared as the source of greenhouse gases,while T4 was the sink of greenhouse gases.