Effects Of Mixed Application Of Desulfurized Gypsum And Biochar On N₂O Emissions From Paddy Fields

N₂O is closely related to the three major global environmental issues-global warming,ozone layer destruction and acid deposition.In recent years,it has attracted attention from researchers.Rice fields are an important source of atmospheric N₂O emissions,accounting for approximately 25%of global nitrous oxide emissions.Therefore,the reduction of N₂O gas emissions from rice fields is of great significance for improving global climate change.Desulfurized gypsum is the main by-product of flue gas desulfurization of coal-fired power plants.It is still listed as a key solid waste in the relevant report issued by the Environmental Development Department of the National Development and Reform Commission in 2019,which shows that it has a lot of room for utilization.Because it is rich in a large amount of sulfur,it can inhibit the methane emission of rice fields by enhancing the activity of sulfate-reducing bacteria after being applied to farmland.More and more researchers suggest that it should be applied to agriculture to reduce CH₄ emissions from farmland.After the farmland,the impact on other gas emissions is gradually paid attention.The rich nutrients in desulfurized gypsum may affect the growth and metabolic activities of nitrifying and denitrifying bacteria,thus indirectly affecting the emission of N₂O.As a new type of material,biochar has a loose and porous structure and special physical and chemical properties,and its research on soil greenhouse gas emission reduction has attracted the attention of relevant scholars.Biochar is rich in organic carbon,which may affect the N₂O emission of farmland by changing the absorption of soil nutrients by plants.At present,most of the researches on N₂O gas emission from desulfurized gypsum and biochar in farmland have focused on the effects of the two materials applied separately on N₂O gas emission from farmland.There are relatively few studies on the mixed application of the two materials.Is rare.In this paper,a yellow soil paddy field in Chongqing was used as the research object,and static dark-box-gas chromatography was used to observe the in situ fluxes of N₂O during rice growth and leisure periods from May 2017 to January 2020.Set B(no rice,no desulfurized gypsum and biochar),CK(no rice,no desulfurized gypsum and biochar),T1(no rice,4 t·hm^-2 biochar),T2(no rice,Application of 4 t·hm^-2 biochar+4 t·hm^-2 desulfurized gypsum),T3(planting rice,application of 4 t·hm^-2 biochar+8 t·hm^-2 desulfurization gypsum),and T4(planting rice,application of 4 t·hm^-2 biochar+16 t·hm^-2 desulfurized gypsum)6treatments.Analyze the N₂O emission laws and emissions of each treated paddy field,analyze the effects of different soil properties on N₂O emissions,and combine rice yield characteristics to provide directions for greenhouse gas emission reduction in farmland and resource utilization of desulfurized gypsum and biochar.The main findings are as follows:1.Dynamic changes of paddy soil propertiesDuring the whole monitoring period,planting rice,single application of biochar,mixed application of desulfurized gypsum and biochar had no significant effect on soil surface temperature,Eh,p H,soil weight moisture content and flooding height(P>0.05),but had no effect on soil The volumetric water content has a significant effect.Compared with treatment B,planting rice had no significant effect on soil volumetric water content during the rice growing season,but it could increase the soil volumetric water content of rice fields during the off-season period by 1.4%to 2.7%.Compared with CK,single application of biochar can increase soil moisture content by 2.5%during the first year off-field period,and has no significant effect on the soil volumetric water content during the rice growth period and the second and third year off-field periods.Mixed application of desulfurized gypsum and biochar will significantly increase soil volumetric moisture content and enhance soil water retention,and the higher the amount of desulfurized gypsum added to the mixed material,the greater the volumetric soil moisture content.2.Impact of rice cultivation on N₂O emissions from paddy soilThe average N₂O emission fluxes of B treatment during rice growth and leisure were 245.5?g N·m^-2·h^-1 and 760.2?g N·m^-2·h^-1,respectively.Compared with CK treatment,rice planting reduced the average N₂O emission flux during rice growth and leisure periods by 94.00%and 80.90%,respectively.The average N₂O cumulative emissions of B treatment during rice growth and leisure periods were 0.52 kg N·hm^-2and 2.25 kg N·hm^-2,respectively.Compared with CK treatment,planting rice can reduce the cumulative N₂O emissions of yellow soil paddy soil during the growth and leisure periods of rice by 94.23%and 75.56%respectively.Planting rice can significantly reduce 77.37%?89.45%of N₂O emissions from yellow soil paddy soil.3.Effect of mixed application of biochar and desulfurized gypsum on N₂O emissions from paddy soilThe average emission fluxes of N₂O from CK treatment during rice growth and leisure were 14.72?g N·m^-2·h^-1and 145.2?g N·m^-2·h^-1,respectively.Compared with the T1,T2,T3 and T4 treatments,the mixed application of desulfurized gypsum and biochar and the single application of biochar had no significant effect on the instantaneous N₂O emissions from the yellow soil paddy soil,either during rice growth or leisure.The average N₂O cumulative emissions of CK treatment during rice growth and leisure were 0.029 kg N·hm^-2 and 0.553 kg N·hm^-2,respectively.During the monitoring period,compared with the T1,T2,T3 and T4 treatments,the mixed application of desulfurized gypsum and biochar and the single application of biochar had no significant effect on the cumulative N₂O emissions from the yellow soil paddy soil.The leisure period of each treatment is the main emission period of rice field N₂O,and the emission amount accounts for about 95%of the whole year.4.Relationship between N₂O release in paddy fields and environmental factorsSoil moisture is an important environmental factor affecting N₂O gas emissions from acid yellow paddy soils.The amount of N₂O release increases exponentially with the volumetric water content of the soil until it reaches a maximum at about 35%water content and then decreases.The optimum soil volumetric water content for N₂O emission from rice fields is between 30%and 40%.Planting rice,single application of biochar,mixed application of desulfurized gypsum and biochar did not change the optimal water conditions for N₂O emissions from rice fields.The maximum N₂O emissions from each treatment occurred between 200 and 400 m V of soil Eh.When the soil Eh was less than 0 m V,N₂O emissions from rice fields were relatively low.The effect of temperature on N₂O gas emission from acid yellow paddy soil was not significant.N₂O emissions from bare land are positively correlated with air temperature and soil surface temperature,while the rice CK,T1,T2,T3,and T4 treatments have no significant relationship between N₂O release and air temperature.5.Effects of Mixed Application of Biochar and Desulfurized Gypsum on Rice YieldCompared with CK treatment,the combined application of biochar,biochar and desulfurized gypsum could significantly increase the plant height of rice from 5.94 to22.00 cm;the effect on the effective panicle number of rice was not significant.Single application of biochar,biochar and mixed desulfurization gypsum can significantly increase the grain yield and biological yield of rice,with yield increases ranging from7.3%to 15.9%and 2.8%to 24.2%,of which 4 t·hm^-2 biochar.The effect of increasing grain yield was the most obvious with 16 t·hm^-2 desulfurized gypsum;mixed application of 4 t·hm^-2 biochar and 16 t·hm^-2 desulfurized gypsum,mixed application of4 t·hm^-2 biochar and 8 t·hm^-2 desulfurization gypsum biological yield increase effect is the most obvious.