Abstract: Northeast China is an important grain production base at the national level. The content of soil organic carbon in this area has been decreasing year by year due to the irrational use. In this study, a total of 444 soil samples were collected from  maize and rice fields (two typical croplands) in Liaoning Province. The contents of soil organic carbon and its components (microbial biomass carbon, necromass carbon, and dissolved organic carbon) as well as their influencing factors were analyzed. The results showed that the contents of soil organic carbon (SOC), microbial biomass carbon (MBC) and MBC/SOC in rice field were higher than those in maize field, while the contents of dissolved organic carbon, bacterial necromass carbon, fungal necromass carbon, and total necromass carbon in rice field were lower than those in maize field. SOC in maize and rice fields had a significant positive correlation with MBC and microbial necromass carbon, while SOC in rice field had a lower slope with MBC and microbial necromass carbon. Results of random forest model analysis showed that soil C/N ratio and fungal necromass carbon were the key factors influencing SOC in maize and rice fields, with higher interpretation for SOC in maize field. There were significant differences in SOC components and key influencing factors between maize and rice fields. Microbial turnover process had stronger influence on SOC in maize field, while soil properties had a dominant influence on SOC content in rice field. This study provides basic data and a theoretical foundation for the scientific regulation of soil organic carbon in the croplands of Northeast China.

Key words: soil organic carbon, microbial biomass carbon, microbial necromass carbon