Characteristics of changes in carbon pools and aggregate stability of coastal reclaimed saline-alkali soil
[Objective]The aims of this study are to explore the characteristics of changes in coastal saline soil with increasing years of reclamation,and to provide theoretical basis for the treatment of coastal saline soil.[Methods]Field plots in different reclamation periods in Dafeng District,Yancheng City,Jiangsu Province were selected.Organic carbon components,carbon pool indicators,and aggregate stability indicators in coastal surface(0-20 cm)and sub-surface(20-40 cm)saline soils reclaimed for 0 years(Y1),around 20 years(Y2),around 40 years(Y3),around 60 years(Y4),and around 100 years(Y5)were investigated to explore their characteristics and influencing factors under different reclamation periods.[Results](1)Various active organic carbon components in the surface soil and HLOC(highly labile organic carbon)in the subsoil generally showed an increasing and then decreasing trend,with a turning point at Y4.Among them,in the subsoil,MLOC(moderately labile organic carbon)did not show significant changes with increasing reclamation years,while LLOC(low labile organic carbon)showed an increasing and then stable trend,with a turning point at Y3.(2)With the increase in reclamation years,the surface soil R0.25(＞0.25 mm aggregate content)and GWD(geometric mean diameter),as well as the subsurface soil MWD(mean weight diameter),exhibited a trend of first rising and then declining,with a turning point at Y4.The surface soil MWD showed a trend of rising initially and then stabilizing,with its turning point also at Y4.The subsurface soil R0.25 and GWD showed a decrease-increase-decrease trend,with turning points at Y2 and Y4,respectively.(3)Correlation analysis showed that in the surface soil,RY(reclamation years)played an important promoting role in aggregate stability indicators,while other ions except NO3-and Ca2+,EC(electrical conductivity),SAR(sodium adsorption ratio),UW(bulk density),and pH value played important hindering roles in aggregate stability.In the subsoil,UW,other ions except NO3-and Ca2+,EC,and SAR were the main factors affecting aggregate stability.(4)Except for A(carbon storage activity)and AI(carbon pool activity index)in the subsoil,aggregate stability indicators were the main influencing factors promoting the increase of carbon pools in both surface and subsoil,while other ions except NO3-and Ca2+,EC,and UW were the main influencing factors hindering the increase of carbon pools.[Conclusion]Reclamation activities reduced the content of soil salt ions in the surface and subsoil of coastal saline soil,increased the content of large aggregates,aggregate stability,content of different active organic carbon components,and carbon pool-related indicators.However,caution should be exercised regarding land degradation after reclamation for more than 60 years.
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