Spatio-temporal Variation Of Soil Nutrients In Huangshui River Basin And Its Affecting Factors In The Past 30 Years

The Huangshui River Basin is a major agricultural base in Qinghai Province.It is a typical agricultural basin and its soil is affected by both man and nature effects.Soil nutrients are important indicators for evaluating soil quality and are of great significance for soil nutrient cycling and sustainable agricultural development.This study selected soil organic matter(SOM),total nitrogen(STN),total phosphorus(STP),and total potassium(STK),which are closely related to agricultural production,as evaluation indicators.Based on the data from the second national soil survey in the mid-1980s(1980s)and the sampled measured data from the "Chinese Journal of Soil Science(Midwest & Western Volume)" in the basin in 2015,using classical statistical and geostatistical methods.The spatial-temporal characteristics and influencing factors of soil nutrients in the surface layer(0~15cm)of the Huangshui River were analyzed and discussed.The conclusions obtained from the study were as follows:(1)According to the average content of sample data in the Huangshui River Basin in the 1980 s,the contents of SOM,STN,and STK belong to the medium level,and the STP content is rich level;From the perspective of the variation coefficient,the four soil nutrients all belong to the medium level,the order of the variation intensity from strong to weak was STP> STK> STN> SOM;From the perspective of spatial structure characteristics,SOM,STN and STP are strong spatial autocorrelation.STK is a moderate spatial autocorrelation.From the perspective of spatial distribution pattern,SOM shows a near "concave" distribution in the space,that is,the hills are high in the surrounding area and the middle valley is low,the content of which is dominated by the medium level,accounting for 62.03% of the basin area.The spatial pattern of STN and SOM are generally in a “concave” distribution,and the overall is of medium-to-superior level;The spatial distribution of STP content is high in the southeast and the western edge,the north-central is low,and the rich and medium-level areas each account for about 50% of the drainage area.The STK showed a trend of increasing gradually from northwest to southeast,and was mainly modium level,accounting for 78.43% of the basin area.(2)According to the average content of the sampling data in the Huangshui River basin in 2015,SOM,STN,and STP are at the first stage of rich level,and STK is at the third stage of medium level.From the viewpoint of coefficient of variation,except that STK is a weak variation,the other nutrients were of moderate variation;From the perspective of spatial structure characteristics,SOM,STN,and STK are moderate spatial autocorrelation,STP is strong spatial autocorrelation.From the perspective of spatial distribution pattern,SOM and STN are similar in distribution,with a strong continuity as a whole showed an increasing trend from southeast to northwest,a rich level,accounting for more than 75% of basin area;STP does not have obvious regularity and directionality in its spatial distribution,the overall content is relatively high,mainly in the first grade;The distribution of STK is uniform,and the whole basin is at the same level,which is three grade,and belong to medium level.(3)After nearly 30 years of change,the average content of soil nutrients in the Huangshui River Basin showed an increasing trend.the order of the changes from large to small was as follows:SOM> STN> STP> STK,of which the average content of STK was slightly decline,the other nutrient contents increase to varying degrees;The variation coefficient of SOM and STK decreased,and the STN and STP increased.From the perspective of spatial distribution changes,the content grade of SOM showed an increasing trend,distributed the basin mountain areas in the north part of the basin and the shallow mountain areas in the central part of the basin,the content unchanged was distributed the basin mountain areas in the northeast and northwest,and the trend of decline was mainly distributed in the shallow mountain areas and Chuanshui areas in the southeast.The STN grade in the shallow mountain areas in the central part of the basin are mainly ascending,the brain mountain areas in the northwest and northeast remain basically unchanged,the shallow mountain areas and the Chuanshui areas in the southeastern are mainly descended;The STP grade is increasing in most areas of the basin,and the unchanged distribution is more fragmented,the reduction zone is very small,interspersed and distributed in the northeastern part of the basin;The STP grade is increasing in the northern part of the basin mountain areas,the brain mountain areas and the shallow mountain areas in the north-central and southern part are basically unchanged,the central and southeast regions are decreasing trend.Overall,with the exception of STP,the other three kinds of nutrient content grade remain unchanged in the brain mountain areas,and the areas of change are concentrated in shallow mountains and Chuanshui areas.(4)The distribution of soil nutrients in the two phases showed varying degrees of variation,natural factors such as climatic factors,elevation,soil type,and human factors such as land use,fertilization,planting structure all caused these variations.Temperature and altitude were positively correlated with SOM,STN and STK,and negatively correlated with STP,precipitation and sand content were significantly negatively correlated with SOM,STN and STK,and positively correlated with STP.In recent years,human intervention in soil nutrients has shown an increasing trend.