Different Exogenous Organic Matter Can Improve The Soil Fertility Of Coastal Saline-alkali Land Impact Study

The coastal saline-alkali land is an important reserve of arable land resources,and its development and utilization are of great strategic significance for ensuring national food security and maintaining China’s rice bowl.Adding exogenous organic matter to drive soil fertility improvement based on salinity reduction measures,is an effective way to promote the transformation of coastal saline-alkali land into agricultural soil.However,the process of organic carbon accumulation and fertility enhancement in coastal saline-alkali soil driven by exogenous organic material under high salinity and high pH conditions remains unclear.In this study,we investigated the effects of different exogenous organic materials(vinegar residue,sewage sludge and vermicompost)in promoting crop growth and yield increase,the characteristics of soil salinity barrier reduction and soil organic carbon accumulation as the core of soil fertility enhancement,and explored the soil aggregation process and main driving factors of soil fertility enhancement driven by exogenous organic materials through correlation and path analysis.The results showed that:(1)One-time application of vinegar residue,sewage sludge,and vermicompost all promoted the growth of barley and maize and increased the yield of barley and maize in saline-alkali soil.With the increasing addition rates of vinegar residue,sewage sludge,and vermicompost,the plant height,biomass,and yield of barley and maize in 2020 and 2021 showed a gradually increasing trend.At the same application rate,the effects of different exogenous organic materials on promoting crop growth and yield increase in saline-alkali soil were in the order of vinegar residue>sewage sludge>vermicompost.At the highest application rate(200 t ha-1),the average annual yield for the 2-year trial period were 5.16,4.62,and 4.13 t ha-1 for barley,and 1.02.0.90,and 0.86 t ha-1 for maize,respectively,in vinegar residue,sewage sludge and vermicompost treatments.(2)One-time application of vinegar residue,sewage sludge,and vermicompost all promoted the reduction of soil barrier factors in saline-alkali soil.With the increasing addition rates of vinegar residue,sewage sludge,and vermicompost,soil electrical conductivity and pH showed a gradually decreasing trend during the twoyear experiment.At the same application rate,the effects of different exogenous organic materials on the reduction of soil barrier factors in saline-alkali soil were in the order of vinegar residue>sewage sludge>vermicompost.At the highest application rate(200 t ha-1),the soil electrical conductivity in the vinegar residue,sewage sludge,and vermicompost treatments in 2021 decreased to 0.26.0.38,and 0.42 mS cm-1,respectively,and the pH decreased to 8.04,8.19,and 8.54,respectively.(3)The application of vinegar residue,sewage sludge,and vermicompost all improved the fertility of saline-alkali soil.With the increasing application rates of vinegar residue,sewage sludge,and vermicompost,soil organic carbon,water-stable aggregates,and nitrogen and phosphorus nutrients in saline-alkali soil showed a gradual increasing trend during the two-year experiment.At the same application rate,the contents of water-stable aggregates(>0.25 mm and 0.106-0.25 mm)in vinegar residue-treated soil was significantly lower than that in sewage sludge and vermicompost-treated soil,while the soil organic carbon content in vinegar residuetreated soil was significantly higher than that in sewage sludge and vermicomposttreated soil.Additionally,the total nitrogen,alkaline nitrogen,and available phosphorus contents in sewage sludge-treated soil were overall higher than that in vermicompost and vinegar residue-treated soil,and the total phosphorus content in vermicompost-treated soil was overall higher than that in sludge and vinegar residuetreated soil.(4)Soil organic carbon accumulation in saline-alkali soil under exogenous organic material addition is closely related to soil aggregate formation,and there is a positive correlation between soil organic carbon content and soil aggregate content in all organic material application treatments.The correlation analysis showed that barley yield in vinegar residue,sewage sludge,and vermicompost-treated saline-alkali soil was significantly and positively correlated with soil aggregate,organic carbon,total nitrogen,total phosphorus,alkaline nitrogen and available phosphorus,and significantly and negatively correlated with soil pH and electrical conductivity.The results of the path analysis further indicate that electrical conductivity in sludge and vermicompost-treated soils had an indirect negative effect on barley yield(sewage sludge:-1.55,vermicompost:-1.17),while electrical conductivity in vinegar residuetreated soil had a direct negative effect(-2.24).In addition,the direct(-4.46)and indirect(5.39)contributions of soil organic carbon to barley yield were higher with vinegar residue than those with sewage sludge and vermicompost,while the direct contribution of soil aggregate to barley yield was lower with vinegar residue than that with sewage sludge and vermicompost.(5)In summary,the application of exogenous organic materials(vinegar residue,sewage sludge,and vermicompost)all contributed to promoting crop growth and increasing yield,reducing soil barrier factors and improving soil fertility in salinealkali soil.Compared with sewage sludge and vermicompost applications,vinegar residue application led to a fast reduction in soil barrier factors and the rapid accumulation of soil organic carbon,which were more beneficial for increasing barley yields in saline-alkali soil.Therefore,vinegar residue is more beneficial to the cultivation of soil fertility in coastal saline-alkali soil.The results not only enrich the scientific theory of improving soil stability,but also provide theoretical guidance and scientific basis for improving and utilizing coastal saline-alkali land.