Relationship between soil inorganic carbon and organic carbon in the wheat-maize cropland of the North China Plain

Soil inorganic carbon (SIC) and organic carbon (SOC) play an important role in the global carbon cycle. However, studying of SIC dynamics has been lacking. This study was aimed at evaluating the distribution of SIC and influencing factors in the wheat-maize cropland of the North China Plain. We measured contents of SOC, SIC, water-soluble Ca2+ and Mg2+ of 24 soil profile (120 soil samples), and applied various analytical methods to evaluate the spatial distribution of SIC and its relationship with other key parameters. Mean SOC content decreased from 9.5 g C kg(-1) in the 0-20 cm to 4.1 g C kg(-1) in 20-40 cm but SIC increased from 8.1 g C kg(-1) (0-20 cm) to 12.1 g C kg(-1) (80-100 cm). On average, SIC stock over 0-100 cm (16.5 +/- 4.7 kg C m(-2)) was more than twice of SOC stock (7.5 +/- 1.4 kg C m(-2)). In general, SIC stock was lower at the sites far away from the Yellow River. There is a significantly positive correlation between SIC and SOC stocks (R = 0.74, P < 0.001) in the cropland of the North China Plain. This study implies that SIC accumulation might be enhanced by an increase of SOC and highlights the importance of SIC in carbon sequestration in arid and semi-arid croplands.