Dynamics of soil organic and inorganic carbon in the cropland of upper Yellow River Delta, China

Soil inorganic carbon (SIC) and organic carbon (SOC) are important carbon reservoirs in terrestrial ecosystems. However, little attention was paid to SIC dynamics in cropland. We conducted a survey in the upper Yellow River Delta of North China Plain. We collected 155 soil samples from 31 profiles, and measured SOC, SIC and soluble Ca2+ and Mg2+ contents. Our results showed that mean SOC content decreased from 9.30 g kg-1 near the surface to 2.36 g kg-1 in 80-100 cm whereas mean SIC content increased from 10.48 to 12.72 g kg-1. On average, SOC and SIC stocks over 0-100 cm were 5.73 kg C m-2 and 16.89 kg C m-2, respectively. There was a significantly positive correlation (r = 0.88, P < 0.001) between SOC and SIC in the cropland. We also found that SIC had a significantly positive correlation with both soluble Ca2+ (r = 0.57, P < 0.01) and Mg2+ (r = 0.43, P < 0.05). Our study suggested that increasing SOC might lead to an increase in SIC stocks in the cropland of North China Plain. This study highlights the importance of SIC in the carbon cycle of China's semi-arid region.