Spatial Distribution Characteristics Of Soil Erodibility K Value In Poyang Lake Basin

In this paper,Poyang Lake Basin,located in the center of the southern water erosion area,was taken as the study area,and the physical and chemical properties of soil except paddy soil in the study area,such as mechanical composition,organic matter,bulk density,nutrient status and p H value,were analyzed by means of data collection,laboratory experiment and runoff plot observation.Through regression analysis and error analysis,a K-value modified EPIC model suitable for Poyang Lake Basin was established.The modified EPIC formula was used to calculate the K value of each soil in Poyang Lake Basin,and the ordinary Kriging method was used to complete the spatial interpolation under the condition of optimal semi-variogram to analyze the spatial distribution characteristics of K value in Poyang Lake Basin.The conclusions of this study are as follows:(1)Soil p H value,bulk density,total potassium and soil depth change in the same direction,while other physical and chemical indexes change in the opposite direction.The physical and chemical properties showed variability in different soil layers.There are different degrees of correlation among the physical and chemical properties,except that total nitrogen,total phosphorus,available phosphorus and available potassium have not reached significant level with other physical and chemical properties,the other indexes are basically significant or extremely significant.The physical and chemical indexes showed weak variability or moderate variability under different land use.Under different land uses in the study area,the order of p H is: medium cover grassland > dry land > high cover grassland > low cover grassland > shrub forest > sparse forest land > forestland.The order of organic matter is forested land > high-covered grassland > low-covered grassland >medium-covered grassland > shrubbery > sparse woodland > dry land.Total nitrogen and alkali-hydrolyzable nitrogen are high in forest land and grassland.The difference of soil total phosphorus under different land uses is weak,and the available phosphorus in dryland is the highest;There is little difference between total potassium and available potassium in woodland,grassland and dryland under different land use.The bulk density and porosity change in the opposite direction,with small bulk density and large porosity in woodland and dry land.Except for high-cover grassland,the mechanical composition of soil under different land uses is mainly characterized by more silt,less sand and clay.After natural soil develops into dryland soil,its physical,chemical and biological properties will change accordingly.The p H value,alkali-hydrolyzable nitrogen,available phosphorus,porosity and silt content increased as a whole,while the total phosphorus content changed little,while the organic matter,total nitrogen,total potassium,available potassium,bulk density,sand and clay content decreased as a whole.(2)The optimal semivariogram models of soil physical and chemical properties include exponential function,spherical function,Gaussian function and linear function.The indexes with block/base ratio less than 25% are soil p H value,total nitrogen,total phosphorus,available phosphorus and available potassium,which show strong spatial correlation and spatial variation is affected by natural factors.The block/basis ratio of other indexes is between 25% and 75%,and the spatial correlation is moderate,and the spatial variation is controlled by both structure and random factors.(3)A modified EPIC model K=0.2244KEPIC-0.0438 was established after regression analysis of estimated k value and measured k value.The modified EPIC model can be verified by the error analysis method,and is suitable for calculating the k value of the study area.(4)The K value of soil in Poyang Lake Basin varies from 0.00283 to 0.04963,with a range of 0.04680,an average value of 0.02381 and a median value of 0.02506.With the increase of soil profile depth,K value also increases.The K value of each layer varied moderately,and the coefficient of variation decreased with the increase of soil depth.There’s a very significant negative correlation between K value and sand content,but a very significant positive correlation between K value and silt content.(5)The k values of the seven land uses in Poyang Lake Basin are as follows: low cover grassland,dry land,shrub forest,medium cover grassland,sparse forest land,forested land and high cover grassland.The spatial variability of K value under different land use shows weak variability or moderate variability.The K value of land use changes in the same direction as the depth of soil,so that the soil erosion resistance decreases and the surface soil erodes,which will aggravate soil erosion.Part of cultivated land soil is formed by natural soil developed by weathered materials after reclamation and utilization,and there is a certain relationship and law between them.There are extremely significant differences in k value under different land uses of the same parent material,and the k value of natural soil will change significantly after reclamation and utilization.Shrub and low-cover grassland are not easily eroded after reclamation and utilization,while other land uses are more easily eroded after reclamation and utilization.The coefficient of variation of k value of different land uses and dry land is between 2.56% and 15.72%,and the k value between them is weak variability or moderate variability.(6)The overall spatial distribution of K value in Poyang Lake Basin is high in the north and low in the south,which is consistent with the regional distribution characteristics of soil physical and chemical properties in the study area to a certain extent.The difference is closely related to different soil types,topography,parent materials,organic matter and land use.The average value of k is 0.02381,and the study area belongs to erodible soil.The low-value areas of K value are mainly distributed in mountainous and hilly areas with high topography,and the representative soils are hemp-sandy loamy red soil,yellow-sandy loamy red soil and hemp-sandy loamy yellow-red soil.The areas with high K value are distributed in Poyang Lake plain and valley between mountains,and the representative soils are eel loamy red soil,eel loamy red soil and red sand loamy red soil.