Effect Of Different Organic Material Additions On Greenhouse Gas Emissions From Saline Sites Effect Of Different Organic Material Additions On Greenhouse Gas Emissions From Saline Sites

Soil salinization is a global problem and saline soils severely restrict plant growth.Exogenous organic matter addition provides positive significance to increase organic matter of saline soil and improve soil fertility for increasing arable land resources,but soil is an important carrier of greenhouse gases such as CO₂,CH₄and N₂O production and emission,and it is more important to pay attention to emission reduction while increasing soil sink.In this study,we propose to use the abandoned saline soils in the western part of the Songnun Plain to return straw to the fields,and return straw and biochar to the fields after different treatments,including the following treatments:（1）CK:blank control group;（2）MSN:straw with nitrogen fertilizer treated with humicides;（3）ASN:straw with nitrogen fertilizer treated with ammonia;（4）SBN:biochar with nitrogen fertilizer（4）SBN:biochar with nitrogen fertilizer.Under the conditions of rationalizing the use of straw resources and improving the quality of degraded saline soils,the greenhouse gas emissions were observed in situ in the field by static dark box-gas chromatography,and the changes of soil hydrothermal environmental factors and soil physicochemical factors were measured,and their effects on greenhouse gas fluxes were analyzed using two years of data from October2020 to October 2022.The main research results are as follows（1）Through two years of field in situ observation of greenhouse gas flux data from saline soils in the western part of the Songnen Plain,it was observed that both time and treatment factors significantly affected greenhouse gas emissions,and the intervention of exogenous organic matter significantly increased CO₂and N₂O emissions,and MSN,ASN and SBN increased CO₂emissions by 152.25%,203.57%and 73.96%on average for two years,and increased 246.61%,450.52%and 188.62%of N₂O emissions,where the surge in CO₂and N₂O emissions was triggered by the follow-up application of N fertilizer.The effect of organic materials on CH₄emissions was uncertain,increasing CH₄uptake or emissions according to natural variations in soil properties.All three GHGs showed obvious seasonal variation characteristics,i.e.,higher respiration rates in the growing season than in the non-growing season,and soil temperature,moisture and microorganisms were the main reasons for seasonal differences in soil respiration rates.In addition,organic material addition significantly increased the GWP compared to CK control.（2）By regression analysis of soil moisture and GHG fluxes,soil temperature and GHG fluxes,it was observed that soil temperature and soil water content were two important components affecting soil CO₂,CH₄and N₂O fluxes,and soil hydrothermal environmental factors showed positive correlations with CO₂,CH₄and N₂O fluxes,respectively,except for CO₂and N₂O fluxes in the CK group,and GHG Except for CO₂and N₂O fluxes in CK group,the relationship between greenhouse gas fluxes and soil hydrothermal environmental factors was significant.Both straw and biochar have certain water and heat retention effects,therefore,higher soil temperature and moisture create good conditions for microorganisms,and frequent microbial activities promote CO₂,CH₄,and N₂O emissions.（3）Through the correlation analysis between soil physicochemical factors and greenhouse gas fluxes,it was observed that soil physicochemical properties such as SSS,p H,NH₄⁺-N,NO₃^--N,and EC could affect soil greenhouse gas emissions,with SSS,p H,and EC mainly playing a positive role.Organic material and nitrogen fertilizer have a catalytic effect on the increase of soil organic carbon content,which in turn plays a catalytic role in CO₂emission;DOC and NH₄⁺-N are important substrates for CH₄production,and the addition of nitrogen and organic matter will increase the substrate concentration,but the application of nitrogen fertilizer in the non-growing and growing seasons has different effects on nitrogen release and soil physicochemical properties,which in turn makes the uptake or emission of CH₄show uncertainty;nitrogen fertilizer will increase the soil nitrogen content and provide more substrate for nitrification and denitrification,thus increasing N₂O emissions.（4）Two years of data showed that among the three organic materials（MSN,ASN and SBN）,ASN caused the most GHG emissions,MSN was the second,while biochar with nitrogen fertilizer（SBN）was a better material for saline improvement in terms of emission reduction.