Study On The Effects Of Different Amendments On Ammonia Volatilization And Greenhouse Gas Emissions From Soda-saline Rice Paddy Fields

Due to a combination of geological formations,geographical location（coastal）,climate and irrational agricultural activities,the global salinization of land is increasing in size and severity,which seriously threatens the security of agricultural production and the sustainable development of regional agriculture.Dryland farming on large areas of soda-saline soils in the Northeastern Plains of China has low productivity;the development of a"rice for alkali"ecological agriculture model,with the application of specific saline soil amendments,is a realistic and successful option for the soda-saline lands of the region.However,research has shown that rice fields are also an important source of greenhouse gas emissions and ammonia volatilisation.Therefore,it is particularly important to understand the characteristics of greenhouse gas emissions,ammonia volatilisation and their possible driving mechanisms under soil amendment application conditions in rice field ecosystems in the sodic saline soil distribution area of Northeast China.In this study,based on existing studies at home and abroad and integrating and analysing the practical results obtained,we propose to apply desulphurized gypsum(G,20 ton ha^-1)and organic fertilizer(OF,30 ton ha^-1)amendments to soda-saline paddy soils and carry out pot simulations to investigate the effects of applying different types of amendments on the main greenhouse gas emissions and ammonia volatilization from paddy saline soils.This study provides a scientific basis for the analysis and screening of sodic saline soil amendments to improve soil fertility,rice yield and nitrogen fixation and emission reduction,as well as the comprehensive management of sodic saline soils.The main findings from the thesis are as follows:（1）Compared with the control group,both desulphurized gypsum and organic fertilizer measures can reduce the cumulative emission fluxes of methane and carbon dioxide.Among them,desulphurized gypsum and organic fertilizer treatment reduced the emission flux of CO₂by 26.18%and 11.62%respectively;desulphurized gypsum and organic fertilizer treatment reduced the emission flux of CH₄ by 78.05%and 65.84%,respectively.However,desulphurized gypsum and organic fertiliser treatment increased the cumulative emissions of N₂O and NH₃.For GWP,the two treatment groups were able to reduce them by 26.21%and11.91%,respectively.（2）Both desulphurized gypsum and organic fertilizers were able to influence mineralisation,GHG emissions and ammonia volatilisation processes in sodic soils by changing soil properties.desulphurized gypsum significantly reduced soil p H,and after the calcium ions in desulphurized gypsum were replaced,the remaining sulphate played a role in neutralising the alkali;organic fertiliser treatment reduced soil conductivity to a certain extent,and the application of amendments increased soil nutrients,promoted the mineralisation and humification of organic matter in the ground,increased the content of organic carbon,total phosphorus and alkaline decomposed nitrogen,and promoted the transformation of NH₄⁺-N to NO₃^--N,thus affecting greenhouse gas emissions and ammonia volatilisation.（3）The application of soil amendments may affect greenhouse gas emissions and ammonia volatilisation in rice fields by influencing the quality of water on the field surface.The desulphurized gypsum had a significant effect on the conductivity of paddy water（P<0.05）,while the salinity,moisture and temperature of field water all affected the conductivity to varying degrees;the NH₄⁺-N content of field water in the desulphurized gypsum and organic fertiliser treatments tended to decrease gradually,while the NO₃^--N content gradually increased until the end of the maturity period;the NH₄⁺-N content of the organic fertiliser treatment was significantly higher than that of the control.N content of organic fertilizer treatment was significantly higher than that of the control;the application of desulphurized gypsum and organic fertilizer significantly increased the total N and total phosphorus content of field surface water,affecting nitrification and denitrification,thus affecting greenhouse gas emissions and ammonia volatilization.（4）Microbial and functional genetic evidence of greenhouse gas emissions and ammonia volatilization in soda-saline rice fields showed that the levels of amo A,nif H genes and nir K genes were significantly reduced by desulphurized gypsum treatment,while organic fertilizer OF treatment increased the relative expression of m RNA of nif H genes in saline soils;the change pattern of nif H in each treatment was consistent with that of soil organic carbon,total nitrogen,alkaline digested nitrogen and total phosphorus The nos Z-encoded nitrous oxide reductase plays an important role in denitrification,which fundamentally affects greenhouse gas emissions and ammonia volatilisation.In summary,desulphurized and organic fertilizers can effectively improve soil physicochemical properties,improve all physiological indicators of rice and increase yields,while reducing greenhouse gas emissions from farmland.Therefore,the application of amendments in soda-saline soils has a profound impact on saline land improvement and management,agricultural economic development and ecological environmental protection.Among them,the comprehensive improvement effect and carbon and nitrogen gas emission reduction effect of soda saline rice fields show that the application of organic fertilizers can better achieve the goals of saline soil improvement and carbon sequestration and emission reduction.