Spatial-temporal Variability Of Soil Salinization And Its Influencing Factors In Hetao Plain In Recent 40 Years

Soil salinization is one of the most important global eco-environmental issues.Soil salinization leads to the serious land degradation.It further leads to the decline of grain yield and evokes eco-environment deterioration.In recent years,with the enhancing of the human activities,the area of global soil salinization continues expanding.And the degree of salinization continues intensifying.Therefore,human activities gradually become the dominant forces intensifying salinization.Human influencing factors have become the leading factor to intensify salinization.Soil salinity is an important soil property.Soil salt content can reflect the degree of salinization.At present,the research on the distribution of salinity is mainly in a certain period of time.Study on influencing factors of soil salinity is mostly about natural influencing factors.However,there are few researches on the dynamic development and human factors under the long-term sequence of soil salinization.Therefore,there are two key issues that need to be further explored.One issue is how to describe the heterogeneity of soil salinization from the perspective of time and space.The other issue is to explore the impact of human activities on salinization in a long time series.Hetao Plain is located in northwest China and has a temperate continental climate.It is a major grain-producing area in northwest China.In recent years,the degree of soil salinization in Hetao Plain has been intensifying.Soil salinization restricts the high-quality development of local agriculture.For this reason,exploring the temporal and spatial variation of soil salt content and human factors in Hetao Plain is conducive to accurately grasp the dynamic development trend of soil salinization.It is of great significance to prevent and control the salinized soil in Hetao Plain and promote the high-quality development of local agriculture.For this purpose,the study selects Hetao Plain as the research area.Based on traditional auxiliary environment variables,study adds remote sensing images of time series vegetation to predict distributions of soil salinity.Multiple linear regression model,random forest model and support vector machine model are used to predict the temporal and spatial variation characteristics of soil salt content in 1988 and 2020.Human influencing factors is quantified by economic social indexes.The grey correlation analysis method is used to explore the influencing factors of soil salinization.Results are obtained as follows:(1)In the study area,there is a great difference in soil salt content data between1988 and 2020.There is the strong spatial heterogeneity.The results show that topographic factors have little influence on soil salinity in plain area,except slope and elevation.In the climatic factors,the correlation between soil salt content and precipitation,evaporation is not significant.Vegetation factor is negative correlated with soil salt content.Time series NDVI can reflect the spatial distribution of soil salt content.It can be used to predict the spatial distribution of soil salt content.(2)Appropriate environmental variables are selected into MLR model,RF model and SVM model to predict soil salinity.Compared with accuracy of these models,the results reflect that RF model has a relative high accuracy.It can better explain the spatial distribution of soil salt content in Hetao Plain.MLR model,RF model and SVM model are used to draw the spatial distribution map of soil salinity.In 1988,the soil salinity was more in the middle and southwest,and less in the northwest and east.In 2020,the soil salt content is high in the middle and low in the east and west.There is a large spatial difference.And the overall value of salt content is high.The spatial distribution map based on the RF model can reflect more detailed characteristics of the spatial distribution of soil salinity.It has better mapping effect.(3)From 1988 to 2020,the soil salt content in most areas of Hetao Plain increased by 0.1% ～ 0.3%.The spatial distribution is characterized by large increment in the middle and small increment in the east and west.A large area of slightly salinized land is transformed into moderately salinized land.Soil salinization is intensified.In all banner counties,the changes of soil salt content in Dengkou county and wulatqian banner show significant spatial heterogeneity.Soil salinization in Wuyuan county is serious.The salinization problem in Dengkou county has eased.The salinization problem in Wulat Front Banner is less prominent.(4)The five indicators that have strong correlation with the average change of soil salinity in Hetao Plain include: Population,effective irrigation area,grain sown area,crop sown area,fertilizer application amount.The human influencing factors related to the change of soil salt content in each banner and county include:population size,agricultural development,irrigation mode and fertilizer application.Cultivation methods and economic development have little influence on the change of soil salt content.Therefore,it is necessary to controlling soil salinization on local conditions.