Effects Of Species And Density Of Lobster On Greenhouse Gas Emissions And Carbon Footprint Under Rice-shrimp Co-cropping

Paddy fields are important sources of atmospheric methane（CH₄）and nitrous oxide（N₂O）.Controlling greenhouse gas（GHG）emission from paddy field is of great significance to reduce agricultural emission and improve agricultural ecological and environmental benefits.The rice shrimp co-cropping model is an emerging paddy field comprehensive cultivation model,which can maintain soil fertility,reduce fertilizer and pesticide application,increase economic income and reduce GHG emissions.However,the relationship between lobster species and breeding density on GHG emissions,carbon footprint and ecological benefits of paddy field system is still unclear.Therefore,in this study,different lobster species and breeding density tests were set up,and a total of 4treatments were set up:rice monoculture（DZ）,rice co-cropping with Cherax quadricarinatus（DA）,rice co-cropping with low-density Procambarus clarkii（DD）,and rice co-cropping with high-density Procambarus clarkii（DG）were used to study the effects of rice shrimp co-cropping on GHG emissions,comprehensive warming potential（GWP）,carbon footprint and ecological benefits of paddy system by the closed static chamber method and life cycle assessment.The main results are as follows:（1）In the parameters of water quality and soil physicochemical properties of paddy fields:Compared with DZ,rice shrimp co-cropping treatment significantly increased the concentration of dissolved oxygen（DO）,soil Eh,soil DOC,soil nitrate nitrogen and soil ammonium nitrogen,and there were no significant differences among the treatments in water pH,nitrate nitrogen and ammonium nitrogen.Among the three rice shrimp co-cropping treatments,DG treatment significantly increased water DO,soil Eh and soil DOC.The main factors affecting GHG emissions in paddy fields were soil Eh,water DO,soil ammonium nitrogen and soil nitrate nitrogen.Soil Eh,water DO,soil ammonium nitrogen and soil nitrate nitrogen were significantly（P<0.05）negatively correlated with CH₄emission,and significantly（P<0.05）positively correlated with N₂O emission.（2）In terms of GHG emissions from paddy fields,the cumulative CH₄emissions from each treatment were as follows:DZ>DA>DD>DG;The cumulative emission the order of N₂O is:DG>DD>DA>DZ;The GWP the order is DZ>DA>DD>DG.Compared with DZ treatment,the cumulative CH₄emissions and GWP of rice shrimp co-cropping under DG,DD and DA were significantly reduced by 43.9%,35.6%and 21.0%,36.9%,30.7%and18.1%,respectively.Compared with DZ treatment,rice shrimp co-cropping significantly increased the cumulative N₂O emissions of paddy field by 43.1%,24.8%and 10.3%,respectively.DG treatment significantly reduced GWP in paddy fields,indicating that the increase of Procambarus clarkii varieties and breeding density in rice shrimp co-cropping could reduce GHG emission in paddy fields.（3）In terms of the comprehensive eco-economic benefits of the paddy system,compared with the DZ treatment,rice shrimp co-cropping treatments significantly reduced GHGI（greenhouse gas emission intensity）of the paddy system,and the trend of GHGI among the four treatments was DZ>DA>DD≈DG;Compared with DZ,DG,DD and DA treatments reduced CF_A（carbon footprint per unit area）by 20.57%,15.32 and 4.87%,respectively.Compared with DZ treatment,DA,DG and DD treatment significantly increased NEEB（net ecosystem economic budget）by 541.12%,526.44%and 356.39%,respectively.In conclusion,rice shrimp co-cropping model is a paddy field comprehensive cultivation model which can improve ecological environment,increase economic income,alleviate greenhouse effect of paddy field,ensure food security and green and low-carbon.Among them,the appropriate increase of breeding density in the rice shrimp co-cropping model can promote the economic,ecological and environmental benefits of the rice shrimp co-cropping model.