Spatial Variability of Soil Organic Carbon Under Maize Monoculture in the Song-Nen Plain, Northeast China

Soil organic carbon (SOC) and its relationship with landscape attributes are important for evaluating current regional, continental, and global carbon stores. Data of SOC in surface soils (0–20 cm) of four main soils, Cambisol, Arenosol, Phaeozem, and Chernozem, were collected at 451 locations in Nongan County under maize monoculture in the Song-Nen Plain, Northeast China. The spatial characteristics of soil organic carbon were studied, using geographic information systems (GIS) and geostatistics. Effects of other soil physical and chemical properties, elevation, slope, and soil type on SOC were explored. SOC concentrations followed a normal distribution, with an arithmetic mean of 14.91 g kg−1. The experimental variogram of SOC was fitted with a spherical model. There were significant correlations between soil organic carbon and bulk density (r = −0.374**), pH (r = 0.549**), total nitrogen (r = 0.781**), extractable phosphorus (r = −0.109*), exchangeable potassium (r = 0.565**), and cation exchange capacity (r = 0.313**). Generally, lower SOC concentrations were significantly associated with high elevation (r = −0.429**). Soil organic carbon was significantly negatively correlated with slope gradient (r = −0.195**). Samples of the Cambisol statistically had the highest SOC concentrations, and samples of the Arenosol had the lowest SOC value.