Effect Of Amendment Application On Carbon And Nitrogen Transformation In Saline Soils

Our country is characterized by large population and insufficient cultivated area.Saline-alkali land thus is a valuable cultivated land reserve resource.The area of saline-alkali land in China is about 9.91×10⁷ hm²,accounting for about 10%of the total saline-alkali land in the world,of which about 36%can be developed and utilized.Addition of soil conditioners is an important means of efficient utilization of saline soils.Amendments,such as gypsum,biochar,organic materials,etc.,could efficiently improve saline soils.The unique physical,chemical and biological properties of saline soils usually lead to a fragile ecological environment.It is of great practical and strategical significance to use comprehensive measures to ameliorate saline soils.Based on the above background,the following experiments were conducted:（1）Biochar,organic fertilizer and gypsum were used in low-salinity soil,moderately saline soil,high-salinity soil and severely saline soil to investigate the influence of conditioners on nitrification process and nitrifying communities,as well as on ammonia（NH₃）volatilization and nitrous oxide（N₂O）emissions.（2）Biochar,organic fertilizer,straw,furfural residue and humic acid were applied in moderate-saline soils to assess the decomposition,transformation and fixed storage of organic carbon in saline soils.The main results were as follows:（1）Amendments promoted nitrification in mild,moderately and severely salinized soils.Biochar,organic fertilizer and gypsum increased the nitrate nitrogen content in high-salinity soil,which could be due to the fact that the amendments relieve salt stress and promotes nitrification（2）Organic fertilizer significantly reduced the cumulative emission of N₂O in low-salinity,high-salinity and severely saline soils,while biochar significantly reduced the cumulative emission of N₂O in high-salinity and severely saline soils.There was no significant difference between the total volatilization of NH₃ in low-salinity and moderately saline soils.Biochar treatment significantly increased the total amount of NH₃ volatilization in high-salinity soil.Both biochar and organic fertilizer treatment could significantly reduce the total amount of NH₃volatilization in severely saline soils.（3）Amendments decreased the copy numbers of AOA-amo A gene,and biochar increased the copy numbers of AOB-amo A genes in high-salinity and severely saline soils.Correlation analysis showed that AOA was positively correlated with nitrate nitrogen and N₂O AOA were mainly grouped into Candidatus Nitrosocaldus（Crenarchaeota）and Nitrososphaera（Thaumarchaeota）.（4）The application of biochar,humic acid,organic fertilizer,straw and furfural residue could increase soil organic carbon content in mildly salinized soil,and the improvement effect followed the trend:humic acid>biochar>organic fertilizer>furfural residue>straw.（5）Exogenous carbon amendments increased soil mineralization,CO₂ emission,and soil organic carbon content.Organic fertilizer,straw and furfural residue significantly increased the contents of microbial biomass carbon（MBC）and soluble carbon（DOC）in saline soils,among which organic fertilizer had the most significant effect,increasing microbial biomass carbon（MBC）by 168.55%and soluble carbon（DOC）by 283.37%compared with blank control.Organic fertilizer,straw,biochar,furfural residue and humic acid increased granular organic carbon（POC）by 197.58⁴40.70%,and the increasing effect was as follows:Organic fertilizer>straw>biochar>humic acid>furfural residue.The effect of foreign organic matter on soil mineral-bound carbon（MOC）was not significantly increased except for humic acid and furfural residue,which increased by 112.28%and 50.92%,respectively.