Effects Of Pig Manure On Greenhouse Gas Emission In Farmland Under Rice-wheat Rotation For 5 Years

In recent years,with the rapid development of intensive agriculture,a large number of chemical nitrogen fertilizer input has brought high crop yield,but also led to farmland non-point source pollution and greenhouse gas emissions have become increasingly prominent.It is of great significance to explore fertilization models that meet the needs of high crop yield,efficient utilization of agricultural resources and low environmental negative effects.Therefore,this study carried out field trials under the rice-wheat rotation system in the Chengdu Plain,setting control(T0),conventional fertilizer N(T1),25%pig manure+75%fertilizer N(T2),50%pig manure+50%Chemical fertilizer N(T3),100%pig manure N(T4),150%pig manure N(T5),200%pig manure N(T6),a total of 7treatments,through continuous field in situ monitoring for 5 years to explore the Chengdu Plain annual variation characteristics and influencing factors of CH₄,N₂O and CO₂emissions of farmland greenhouse gases under different conditions of continuous application of pig manure in the rice-wheat rotation system,as well as the comprehensive warming potential and greenhouse gas emission intensity of continuous pig manure return to the field,to comprehensively evaluate the agricultural production benefits and environmental pressures caused by the continuous return of pig manure to the field,and provide a theoretical basis for the rational use of livestock waste.The main results of this paper were as follows:(1)In the rice-wheat rotation system,the emissions of CH₄,N₂O and CO₂ from different ratios of pig manure continuously returned to the field had obvious seasonal characteristics,and the annual dynamic changes for 5 consecutive years were basically the same.CH₄ emissions were concentrated in the rice season,and CH₄ emissions increased significantly with the increase of the proportion of pig manure application;N₂O emissions were significantly reduced by 100%pig manure N treatment,and increased by 150%and200%pig manure N treatments;CO₂ emissions were higher in the wheat season than in the rice season,and pig manure application increased CO₂ emissions by 5.02%and 63.49%.The cumulative emissions of N₂O and CO₂ continued to increase year by year,and the continuous growth of emissions for 5 consecutive years did not slow down,while the growth rate of CH₄ cumulative emissions of nitrogen replacement treatment such as pig manure(25%-100%pig manure N)gradually slowed down,but the excess pig manure treatment(150%and 200%pig manure N)did not slow down.(2)CH₄,N₂O and CO₂ emissions from rice and wheat were affected by many environmental and soil factors.Daily mean temperature,air box internal temperature,5cm soil temperature and soil moisture significantly affected soil CH₄,N₂O and CO₂ emissions from rice and wheat crops,and soil NH₄⁺-N,NO₃^--N and SOC contents in rice and wheat crops were the main factors affecting soil CH₄,N₂O and CO₂cumulative emissions.Pig manure application rate and application years had significant interactive effects on CH₄emissions,only wheat season had significant interactive effects on N₂O and CO₂emissions.The interaction between pig manure application rate and application years in rice-wheat rotation only significantly affected the cumulative emission of CH₄,but had no significant effect on the cumulative emission of N₂O and CO₂.(3)The research results for 5 consecutive years show that the application of pig manure in rice season can increase the total warming potential(GWP),mainly by CH₄emission(the contribution rate to total GWP is 85.34%-96.15%),with an increase of7.25%-372.13%.The N₂O emission with a contribution of more than 90%to total GWP can be reduced by 0.72%-34.74%when the appropriate combined application of pig manure and chemical fertilizer(25%-100%pig manure N)in wheat season.In terms of annual greenhouse gas emissions from rice-wheat rotation,pig manure application increased total GWP,and mainly CH₄ emissions(the contribution rate to total GWP was60.66%-73.29%),with an increase of 7.46%-384.44%.(4)In the rice-wheat rotation system,the 5-year GHGI value of 25%pig manure+75%chemical fertilizer N treatment(T2)was not significantly higher than that of chemical fertilizer(T1)treatment,and the rice-wheat yield was significantly increased.Although 50%pig manure+50%chemical fertilizer N treatment(T3)significantly increased the average value of GHGI for 5 years,it had no significant effect on the annual GHGI value,and the rice and wheat yield of this treatment reached the maximum,with better greenhouse gas control and optimal agronomic benefits,and can be used as an optimized fertilization technology model for both production and environmental benefits.Although the treatment of 100%pig manure N and its above ratio(T4?T6)still had good agronomic benefits,it had a continuous increasing effect on CH₄ emission in rice season and N₂O emission in wheat season,and its warming potential(GWP)and greenhouse gas emission intensity(GHGI)increased significantly,so it was not suitable to be popularized and applied in rice-wheat rotation system in Chengdu Plain.