Spatio-temporal Variation Of Soil Salinity And Sodicity In Newly Reclamated Tidal Flats

With the advancement and deep going of "LOICZ" plan,the study about interactions between land and ocean in the coastal zone has become a hot topica which is paid much attention by the scholars.The harmonious pattern between human and the nature is broken,due to the Population growth and economic development rapidly.With the contradiction between the Population-Resources-Environment the coastal mud flat as important reserve land resource has become the focus of exploitation.And the number of coastal mud flat of Jiangsu province accounts for 1/4 of the total of all the country.As the largest area of the mid-latitude tidal flats in the world with the most comprehensive land use types,Jiangsu province has the superior advantageous conditions for the development and utilization of the reclamation and has made great social and economic benefits.However,quite a long time,from the current and future,the soil salinization of north Jiangsu coastal will continue to be the main reasons for restrict the development and utilization of soil in this area.Compared with the saline soil of inland and flatlant,the high NaCl content of saline soil and the underground water level become the most direct factors which are limiting crop growth.At the same time,in the face of the current situation,more population and little land,the land pressure increasing from the population and industry,and the land bearing capacity is more than critical limit in Jiangsu province has become a serious restricting factor for the development of the economy and society.Under the pressure the problem of how to fast,precise and effective exploitation of coastal resources are in urgent need of the guidance from the scientific method.The present study of the land reclamation area most have longer reclamation years and the changes of soil physical and chemical properties and the spatial differentiation of new reclamation are more strongly than the longer period which is in the crucial stage of soil desalinization and soil dealkalization even to improve the soil salinization.In the face of such situation,in view of the study of new reclamation with shorter years is worth to cause the attention of scholars.Therefore this thesis regards the Yudong reclamation area of Rudong as study area,which had reclamtion from 2007 and agricultural use of oriented.Combining GIS and geostatistics,by introducing gathered coefficient,using the basic statistics model and the corresponding analysis,Pearson correlation coefficient,etc.,to carry out the study of temporal-spatial variability and its correlation of soil salinization in different seasons,in different land use types and its environmental factors.The results are as follow:(1)The soil from new reclamation district most for sodic alkaline earth,the salt injury degree is reach to the the severe level.Different from the studies before which are concluded that the seasonal characteristics of coastal saline soil is desalination in summer and salification in summer,the seasonal characteristics of Yudong reclamation area with high salt in summer,with low salt in winter,the surface salt in summer is lower than winter.Yudong still has the part of the natural characteristics of the reclamation area that has high salt alkaline,and the largest conditions of these natural features of reclamation soil salinity and crop production influence is buried depth of groundwater.This makes new reclamation district soil salinization has obvious seasonal repeatability,soil in the salt deposition and desalting repeatedly under the influence of groundwater.(2)The process of dealkalization is more complex and slower than the process of desalination.The soil desalting rate faster,and the soil alkalization degrees of decline will lag the desalting process at new reclamation district.The change of soil pH in the study area is mainly influenced by soluble Ca2+ content in the soil,pH and Ca2+ show the relationship between the increase or decrease.The high variability of salinity is one of the main features of the new reclamation district,surface soil have the strongest salinity variability and gradually decreased with the soil deepen.The soil salinity variability in winter is stronger than in summer.Change the way of land use is an important cause of the reclamation area overall salinity seasonal difference and human factors of land use change and natural factors of land cover vegetation succession increases the differences in changes in reclamation of saline alkali soil,and so on the use of reclamation area and reasonable development and supervision for the improvement of soil salinization has a crucial role.(3)The removal effect of desalting alkali on the new reclamation area of woodland and reeds were best,aquaculture not only limited the soil desalting,may also caused the accumulation of salt in the surface soil salt in the progress of drainaging.Wheat and Sesbania planting have good desalination effects in condition of either low salt or high salt soil.The effect of corn plant desalination is not obvious,but it also has a good control effect on the profile of salt.In natural conditions,soil desalinization has a natural succession of wetland-suaeda-couch grass-reed.The vegetation distribution on the unused land in a certain extent can qualitatively reflect soil salinization and soil physical properties in newly reclamation.When the salt marsh vegetation natural succession to the thatched or reed stage,are indicating that the salinity of soil surface has dropped to the stage that primary agricultural can be developed.But in the farmland,to prevent accumulation of salt in the surface soil salt on winter caused by the complicated groundwater conditions which is critical for management.(4)The spatial correlation of surface soil salinity is weak of this reclamation,soil salt content by the impact of human activities such as cultivation,irrigation and other random factors.Bottom soil has a moderate degree of spatial correlation,the spatial distribution is mainly caused by the common influence of random factors and soil parent material,climate and other structural factors.With the increase of soil depth,the spatial correlation of salinity gradually increased,from mainly affected by human activities gradually into by the structural factors of rainfall,groundwater depth,terrain effects.The salt in space distribution reflects the low-high-low-high from south to north in the reclamation area,and sporadic mixed with the distribution of moderate salinity;The SAR distribution from south to north is continue to reduce with the gradient difference.The salt and SAR showed the trend of decreasing from inland to the sea.Therefore the management of soil salinization in the farmland reclamation also need to focus on prevention the soil salinization of inland area.