Effects Of Exogenous Organic Carbon On The Formation And Stability Of Soil Aggregates In A Mudflat Soil

The mudflat along the east coast of China is an important reserve cultivated land resource On the basis of desalination measures,adding exogenous organic materials to drive the formation of soil aggregates in mudflats is the premise of restraining salt accumulation in the surface soil,improving fertility and promoting the transformation of mudflat soil into agricultural soil.However,many mechanisms in this process remain unclear,such as how different organics drive the formation and stability of aggregates?and how do soil environmental factors including high salinity,high pH and water content affect the formation and stability of aggregates in mudflats?In this study,field experiments were conducted to investigate the effects of different application rates(25,50,100,200 t ha-1)of sewage sludge and vermicompost on the formation and stability of soil aggregates in mudflats.The effects of glucose,microcrystalline cellulose,chitosan and chitin on the formation and stability of soil aggregates in mudflats were studied by indoor incubation experiment under the condition of equal carbon addition.The effects of different soil pH,salinity and water content on the formation of soil aggregates in mudflats were also studied through indoor experiments.The results showed that:(1)The application of sewage sludge and vermicompost both promoted the formation of>0.25 mm aggregates in mudflat soil.With the increase of the amount of organic material applied,the number of aggregates showed an upward trend.After 6 months and 12 months of application of vermicompost,the effect of increasing the number of>0.25 mm aggregates in mudflat soil was better than that of sewage sludge.With the increase of the amount of sewage sludge and vermicompost applied,the organic carbon content of the mudflat soil gradually increased.There existed a positive correlation between the number of>0.25 mm aggregates in the mudflat soil and the organic carbon content in the two tested periods,and this correlation was closer in vermicompost treatment than that in the sewage sludge treatment(2)In the indoor experiment,glucose,micro crystalline cellulose,chitosan,and chitin applied in equal amount of carbon all promoted the formation of>0.25 mm aggregates in mudflat soil.The microcrystalline cellulose showed the best promotion effect on the formation of>0.25 mm aggregates in mudflat soil,and the number of aggregates was significantly higher than that of the control at each application rate.The overall promotion effect of chitosan was the worst,and only under the conditions of 1.5%and 2.0%carbon addition,the number of>0.25 mm aggregates in mudflat soil was significantly higher than that in the control.(3)The formation of>0.25 mm aggregates in the soil applied with organic molecules was affected by mudflat conditions.There was a significant negative correlation between the number of>0.25 mm aggregates and soil pH in mudflat soil applied with glucose and chitin.While there was a significant positive correlation between the number of>0.25 mm aggregates and pH in the mudflat soil applied with microcrystalline cellulose.The number of>0.25 mm aggregates in mudflat soil applied with glucose,microcrystalline cellulose,chitin,and chitosan decreased with the increase of soil salt content.As the soil salinity increased,the number of>0.25 aggregates in soil with application of glucose and chitin mm decreased significantly.With the increase of soil moisture content,the>0.25 mm aggregates of mudflat soil with glucose,microcrystalline cellulose,chitosan,and chitin all showed a downward trend.(4)Infrared Spectral Analysis showed that the application of sewage sludge and vermicompost both increased the content of aromatics,alcohols or ethers,carboxylic acids,aliphatics and carbohydrates in>0.25 mm aggregates of mudflat soil.However,the increment of organic functional groups and active carbon content in>0.25 mm aggregates of mudflat soil treated with sewage sludge was higher than that with vermicompost.