Spatial Distribution Characteristics Of Soil Carbon And Nitrogen In Dagangshan Watershed Of Jiangxi Province Based On NDVI And Topographic Factors

Spatial distribution of soil carbon and nitrogen content and its influencing factors is the important research contents of the global carbon and nitrogen cycle.We studied the spatial distribution characteristics and influencing factors of soil carbon and nitrogen in forest vegetation in red soil region of southern China by using the surface soil of the Dagangshan watershed where is a typical region in red soil regions of southern China as the research object.Taking into account the factors such as vegetation type,topographic condition,accessibility,and uniformity of spatial distribution in the study area,we set up 90 sampling points and collected 270 soil samples in July 2015 and July 2016.The effects of vegetation and topography on the spatial distribution of surface soil carbon and nitrogen elements in the basin were studied by geostatistics relevant theories and ArcGIS,ENVI,SPSS software platforms.Additionally,we also used different spatial prediction methods for soil carbon and nitrogen elements to analyze the spatial distribution characteristics of surface soil carbon and nitrogen content in the basin.At the same time,we compared and explored different methods of spatial prediction.The main findings are as follows:(1)The average contents of soil organic carbon,total nitrogen,and available nitrogen nitrogen in the surface(0~20 cm)soil of Dagangshan watershed were 25.82 g/kg,1.63 g/kg,and 126.67 mg/kg,respectively.The coefficient of variation of soil organic carbon,total nitrogen,and available nitrogen was between 25% and 60%,both of which were moderately variable.Among them,soil organic carbon had the highest degree of variation(58.33%),followed by alkaline dissolved nitrogen(45.10%).And total nitrogen had the lowest degree of variation(26.99%).The soil carbon and nitrogen contents under different vegetation types were significantly different.Soil organic carbon was represented as Masson pine forest> farmland> Chinese fir plantation> Broadleaved forest> Moso bamboo plantation> Coniferous and broadleaved mixed forest> grassland.Soil total nitrogen was represented as Masson pine forest> farmland> Chinese fir plantation> Moso bamboo plantation> Coniferous and broadleaved mixed forest and Broadleaved forest >Grassland.Soil available nitrogen showed Coniferous and broadleaved mixed forest> Broadleaved forest> Chinese fir plantation> Masson pine forest> farmland> Moso bamboo plantation> grassland.Soil carbon and nitrogen contents were significantly different under different soil thicknesses.The average contents of soil organic carbon,total nitrogen,and available nitrogen nitrogen in the 0~10 cm layeres were 32.39 g/kg,1.80 g/kg,and 152.66 mg/kg,respectively.In the 10~20 cm layeres,the average content was 19.25g/kg,1.46g/kg and 100.69mg/kg,respectively.The content of soil carbon and nitrogen in 0~10cm layeres was obviously larger than 10~20 cm layeres.(2)There was a significant positive correlation between soil organic carbon,total nitrogen and available nitrogen in surface soil(0~20 cm)in Dagangshan watershed.The correlation coefficients were 0.93 and 0.88,respectively.And the spatial distribution of soil carbon and nitrogen elements was closely related.Soil organic carbon,total nitrogen,and available nitrogen were positively correlated with NDVI,elevation,slope,and TWI,but negatively correlated with WPI and STI.Vegetation and topographic factors significantly affected the spatial distribution of soil organic carbon,total nitrogen,and available nitrogen.(3)The Co-Kriging is more accurate in predicting the spatial distribution of soil carbon and nitrogen.And the prediction accuracy of soil organic carbon,total nitrogen,and available nitrogen is 77.5%,76.9%,and 77.1%,respectively.Spatial distribution pattern of organic carbon and total nitrogen in the topsoil of the Dagangshan watershed was high in the northwest,low in the southeast,and gradually decreased from northwest to southeast.This distribution trend is basically consistent with the trends of DEM trend and NDVI distribution in the basin.The content of soil available nitrogen was more in the northwest of the river basin,but there was no significant difference in other areas.