Objective  The Sanjiang Plain is an important grain producing area in China. The spatial distribution characteristics and influencing factors of soil organic carbon (SOC) content and density were explored in the Sanjiang Plain, so as to provide an important basis for the maintenance and promotion of SOC pool in this area.

  Method  A total of 324 surface (0-20 cm) soil samples were collected through the 8 km × 8 km grid distribution in the Sanjiang Plain, and the spatial distribution characteristics and influencing factors of SOC content and density were analyzed.

  Result  The mean value of SOC contents in surface layer was 30.90 ± 25.42 g kg⁻¹, the mean value of SOC density in surface layer was 69.05 ± 48.62 t hm⁻². The spatial distribution characteristics was high in the southeast and northwest. By analyzing the influencing factors of SOC distribution, it was found that there were very significant differences of SOC contents between Black soil and paddy soil (P < 0.01), Black soil and Dark Brown soil (P < 0.05). The lowest SOC content of paddy soil was 27.21 g kg⁻¹, the highest SOC content of woodland was 44.83 g kg⁻¹, and there was significant difference between cultivated land and woodland (P < 0.01). Within all types of crops, the lowest SOC content of rice was 27.31g kg⁻¹, the highest SOC content of mixed forest was 44.83 g kg⁻¹, and there were significant differences between mixed forest and maize, rice and beans (P < 0.01).

  Conclusion  In general, SOC content and density of surface soil in the Sanjiang Plain are related to soil types, land use types and crop types.