Spatial variability of soil magnetic susceptibility, organic carbon and total nitrogen from farmland in northern China

Abstract

Spatial variability of magnetic susceptibility (χ), soil organic carbon (SOC) and total nitrogen (TN) concentrations were analyzed using geostatistics method in different soil horizons from farmland in the North China. Results showed that a significant difference in SOC and TN contents, while no significant difference in χ was observed at two soil horizons using the t-test. The average values of χ 93.0×10−8m3kg−1, SOC 11.25gkg−1 and TN 1.03gkg−1 were higher at the 0–20cm than those measured at the 20–40cm depth, respectively. The value of frequency dependent susceptibility (χfd) was greater than 6% indicated the formation of superparamagnetic particles through pedogenesis and/or human activities. The isotropic semivariogram models of χ, SOC and TN were fitted to spherical model. A clear variogram of soil properties with a medium spatial dependent was observed. The range of spatial correlations was determined to be approximately12km, which seemed to be characteristic for a regional scale. The kriging interpolated maps provided information for soil monitoring and management. Geometric and small spherical magnetic particles were identified by microscopy. Vertical distributions of soil properties proved that soil magnetic signature mainly originated from lithogenic and anthropogenic contribution.