Analysis of spatial variability and influencing factors of topsoil organic carbon and total nitrogen in Hebei Province

【Objectives】 In terrestrial ecosystem, soil total nitrogen and organic carbon are important ecological factors. In this paper, spatial distribution characteristics of soil organic carbon and total nitrogen are studied using spatially surveyed soil profile information. It is expected that the outcomes of this study can provide scientific basis not only for monitoring and managing soil nutrients, but also for cost-effective soil sampling planning in the similar regions. 【Methods】 Both traditional statistic and semi variogram methods are used to study the spatial variability of total nitrogen and organic carbon of the soils. And the distribution patterns of soil total nitrogen and organic carbon are examined using Ordinary Kriging and Regression Kriging.【Results】 The means of soil organic carbon and total nitrogen in the study area are 15.25 g/kg and 1.23 g/kg respectively. And the variance coefficients were 0.73 and 0.63 respectively, which are explained as medium spatial variability. The log transformed soil organic carbon and total nitrogen contents have normal distribution. The theoretical semi-variogram models of soil organic carbon and total nitrogen are all fitted with spherical model well. The nugget and sill ratios of soil organic carbon and total nitrogen are 1.8% and 1.2% respectively. Nugget coefficient of organic carbon and total nitrogen is less than 25%, which indicates that organic carbon and total nitrogen are strongly spatial correlated. Spatial heterogeneity ranges of organic carbon and total nitrogen are different. The range value for soil organic carbon is 50.400 km, while that for total nitrogen is 59.200 km. The overall distribution trend of soil organic carbon in this region is that it is higher in the North than in the South. Although the spatial distribution pattern of the total nitrogen is similar with the soil organic carbon, the spatial variability of organic carbon is significantly higher than that of total nitrogen. The influence of temperature and latitude on spatial variability of the soil organic carbon is more significant than other factors such as soil texture and land use. Based on the predicted values between ordinary kriging and regression kriging, regression kriging not only can reflect the local variation of organic carbon and total nitrogen in the Southeast area, but also can reveal the relationship between carbon, nitrogen, and topographic and climatic factors in the Northwest mountainous area.【Conclusions】 Spatial variability and distribution characteristics of soil organic carbon and total nitrogen are similar, which are related with topography, geomorphology and climate etc. Between regression and ordinary kriging, the regression kriging is more suitable to predict spatial distribution of soil organic carbon and total nitrogen.