Spatial Distribution of Pedogenic Carbonate in the Cropland of North China Plain: Impacts of Soil Organic Carbon and Salts

There is evidence of the carbon sequestration of pedogenic carbonate (PIC) than soil organic carbon (SOC) in arid and semi-arid lands. However, little is done to assess the magnitudes and variability of PIC in semi-humid regions, in which soil carbonate (SIC) often exceeds SOC. Our previous studies have showed that there was significantly positive correlation between SIC and SOC in the northern China's cropland. Here, we hypothesize that the correlation may be related to accumulation of PIC, and conducted a study in a typical cropland located at the lower reaches of the Yellow River sub-humid areas of the North China Plain. Our data revealed a large spatial variation in SOC stock (2.6 - 12.6 kg C m-2) and PIC stock (1.7 - 15.7 kg C m-2) over 0-100 cm, with relatively higher values in the Yellow River Delta. Stocks of soluble Ca2+ and Mg2+ over 0-100 cm were significantly higher in the Yellow River Delta (44-330 g m-2 and 24-226 g m-2) than in the Hebei Plain (79-185 g m-2 and 19-99 g m-2). PIC stock had a significantly positive correlation with SOC stock, but SIC showed no significant correlation with SOC. Although there was no significant correlation between PIC and Ca²⁺+Mg²⁺, partial correlation analyses indicated that PIC stock was negatively correlated with Ca²⁺+Mg²⁺ in the Yellow River delta. Through comparative analyses with other studies, we postulate that climate factors and soil conditions, in addition to the sources of carbon and calcium/magnesium, have large influences on the accumulation of PIC. Integrated studies with quantitative approaches are needed to improve our understanding of transformations of key carbon forms in various ecosystems.