Effects Of Returning Different Organic Materials On Organic Carbon Sequestration And CO₂ Emission In Mollisol

In order to clarify the changes of soil fertility after returning organic materials with different carbon stability from corn straw to the field,explore the characteristics of soil organic carbon sequestration and The law of CO₂ emission,and scientifically evaluate the effect of soil fertilizer cultivation and carbon sequestration and emission reduction of organic materials to the field.In this study,five treatments including CK（no fertilizer）,NPK（chemical fertilizer alone）,NPK+ST（chemical fertilizer combined with straw）,NPK+CP（chemical fertilizer combined with compost）and NPK+BR（chemical fertilizer combined with biochar）were selected as the platform of organic fertilizer cultivation and positioning experiment started in 2011.The changes of soil physical and chemical properties,interannual yield,soil organic carbon content and storage,chemical grouping characteristics and soil CO₂ emission were discussed.By estimating the income and expenditure of soil carbon,the greenhouse effect of returning different kinds of organic materials to the field was clarified,in order to provide a theoretical basis for optimizing the mollisol organic fertilizer cultivation and enhancing the mollisol carbon sink function.The research results of this paper are as follows:1.Returning organic materials to fields for many years improved soil physical and chemical properties and soil fertility.Compared with NPK treatment,NPK+BR treatment significantly reduced soil bulk density in 0-10 cm and 10-20 cm layers.NPK+CP and NPK+BR treatments significantly increased soil moisture content and p H in 0-10 cm soil.The yield and biomass of all fertilization treatments fluctuated,and NPK+CP treatment was beneficial to increase maize yield.2.The soil organic carbon content increased year by year with the addition of organic materials.Compared with the initial stage of the experiment,the soil organic carbon content of NPK+ST,NPK+CP and NPK+BR treatments all increased,and the soil organic carbon content of NPK+BR treatment was the highest.Accordingly,NPK+BR had the highest soil organic carbon storage in 0-20 cm soil layer,reaching59.4 t/hm².Its carbon sequestration rate and carbon sequestration efficiency were 1.70t/hm²/a and 34.1%,respectively,higher than other treatments.3.Returning organic materials to the field increased the content of active organic carbon and inert components of soil,and changed the distribution ratio of organic carbon components.Compared with NPK treatment,NPK+CP and NPK+BR treatments significantly increased the content of highly active organic carbon in each soil layer.NPK+BR treatment had the most significant increase in inert organic carbon content,while NPK+ST and NPK+CP treatments had a slightly lower inert organic carbon content.In terms of the distribution proportion of soil organic carbon,the proportion of inert components was increased by returning organic materials to the field,and NPK+BR treatment had the highest increase in the proportion of inert components.Returning organic materials to soil increased soil microbial content and changed soil enzyme activities closely related to carbon cycle.4.Among all organic material treatments,NPK+CP treatment had the highest emission flux peak and average emission rate,with an average of 828.2 mg/（m²·h）and322.8 mg/（m²·h）,respectively.Correspondingly,its cumulative emission was the highest,with an average of 11 869.1 kg/hm².Soil CO₂ emission flux was significantly positively correlated with soil temperature and air temperature,and NPK+CP treatment had the lowest correlation coefficient and decreased sensitivity to temperature.The carbon sequestration capacity of all fertilization treatments was higher than that of no fertilization treatment,and NPK+BR treatment had the lowest comprehensive warming potential,followed by NPK+CP treatment.In conclusion,long-term organic material returning to field can improve soil physical and chemical properties and increase maize yield,and NPK+CP treatment has the best yield increase effect.Among the treatments of different organic materials,NPK+BR treatment significantly increased soil organic carbon storage,and the proportion of inert organic carbon was the highest.NPK+BR treatment plays an important role in improving soil carbon sequestration ability and reducing CO₂emission.Compared with other organic materials,NPK+BR treatment has the lowest comprehensive warming potential,so it has the most outstanding carbon sequestration and emission reduction effect.