Spatial-temporal Characteristics And Influencing Factors Of Soil Salinization In Cangzhou City Based On Landsat Data

Saline-alkali land is one of the most important reserve cultivated land resources in China.The comprehensive utilization and treatment of saline-alkali land is of strategic significance to national food security.To strengthen the development,utilization of saline-alkali lands and increase their production capacity is a major measure to implement the strategy of "storing grain in land and storing grain in technology",which is of great significance in responding to international changes.Soil salinization is the result of climate,hydrology,geology and human activities.Soil salinization has posed a serious threat to the safety and sustainable development of agriculture.Therefore,using remote sensing technology can be used to quickly obtain the characteristics of soil salinization and analyze the temporal and spatial variation characteristics of the distribution of saline-alkali land,which is conducive to the comprehensive utilization of saline-alkali land.This study,Cangzhou City,a typical coastal alluvial plain area,was selected as the research area.Landsat ETM+/OLI was used as the data source,and the greenness index after K-T transformation was used as the vegetation index.Combined with the salt index,the soil salinization degree inversion model was constructed,and the accuracy of the prediction results was verified.Using the inversion model,the spatial distribution of soil salinization degree in 2000,2010 and 2020 in the study area was inverted,and the spatial-temporal evolution law of Cangzhou city in the past 20 years was analyzed.Finally,combined with the data of climate,hydrology,geology and human activities,the influencing factors of soil salinization in Cangzhou City were analyzed,and the main conclusions were as follows:(1)A classification model of soil salinization degree based on greenness index and salinity index was constructed.Soil salinity data of Haixing Site was measured by field investigation and measured data analysis,and remote sensing data were analyzed and compared based on different methods.In this paper,k-T transform greenness index and salt index SI were selected to construct the spectral index of soil salinization monitoring model.The results showed that the correlation coefficient between SDMI(Salt Detection Model Index)and soil conductivity was 0.889,and the decisive coefficient was 0.790,which was higher than the correlation between NDVI and EVI and salt index.It shows that the greenness index after K-T transformation is more suitable for coastal alluvial plain and can effectively extract regional soil salinization degree information.(2)The spatial-temporal variation characteristics of different degrees of saline-alkali land in Cangzhou city were clarified.The spatial and temporal patterns of salinized soil distribution in Cangzhou city from 2000 to 2020 were analyzed from the perspectives of quantity,structure and transformation type by using the methods of inter-annual and inter-annual area change index and dynamic attitude of land use.The results showed that the degree of soil salinization in the study area showed an obvious trend of differentiation between southwest and northeast,that is,the degree of soil salinization in the southwest area of Cangzhou city was low,mainly non-salinization and mild salinization,while the degree of soil salinization in the coastal area was high,mainly medium and severe salinization.In 2000,the non-salinized and slightly salinized land area in Cangzhou accounted for 16.23% and19.54% of the total land area in the study area,while in 2020,the non-salinized and slightly salinized land area accounted for 22.19% and 23.57% of the total land area in the study area.From 2000 to 2020,In Cangzhou city,the proportion of non-salinized area increased by5.96%,that of mild salinized area also increased by 4.03%,and that of severe salinized area decreased by 11.14%.(3)The driving force of salt-alkali land change in Cangzhou city was systematically analyzed.In cangzhou city 2000,2010 and 2020,three images of saline-alkali land with climate,hydrology,DEM,population and economic structure,residents and crop spatial overlay analysis of data,found that the spatial distribution of saline-alkali and environmental background elements in spatial distribution has some spatial coupling relationship,precipitation and negatively correlated with degree of salinization,The development of population and economy aggravates the degree of salinization and directly affects the planting types and yields of crops.The spatial differentiation of natural elements and human elements affected the spatial and temporal patterns of saline-alkali soil distribution.