Dynamics of pedogenic carbonate in the cropland of the North China Plain: Influences of intensive cropping and salinization.

(a) Distributions of mean stocks of soil organic carbon (SOC), peodgenic carbonate (PIC) and lithogenic carbonates (LIC) over 0–100 cm in the north China, and spatial distributions of (b) SOC and (c) PIC over 0–100 cm in cropland of the North China Plain, and (d) the relationship between PIC and SOC stocks. • PIC stock was significantly larger than SOC stock over 0−100 cm in the cropland of the North China Plain. • There was a significant positive correlation between PIC and SOC stocks. • Intensive cropping resulted in an increase in both SOC and PIC stocks in the semi-humid region. There is evidence of higher levels of pedogenic carbonate (PIC) than soil organic carbon (SOC) in cropland, and a positive relationship between PIC and SOC in salt-affected soils of arid and semi-arid regions. This study is designed to test the hypothesis that PIC is influenced by intensive cropping and salinization in semi-humid regions, in which soil carbonate (SIC) often exceeds SOC. We select a typical cropland with a maize-wheat rotation in the North China Plain, which covers two distinct regions, i.e. the Hebei Plain (HBP) under intensive cropping and the Yellow River Delta (YRD) under soil salinization. Our data show large variations in soil carbon stocks, with slightly higher values for PIC (3.9–14.5 kg C m−2) relative to those of SOC (2.2–9.2 kg C m−2) in the top 1 m. On average, SOC stock is 5.65 kg C m−2 in the YRD, which is slightly lower than in the HBP (6.21 kg C m−2); SIC is significantly higher in the YRD (16.9 kg C m−2) relative to the HBP (13.7 kg C m−2). However, PIC stock is smaller in the YRD (8.67 kg C m−2) relative to the HBP (9.41 kg C m−2). Despite no clear SIC-SOC relationship, there exists a significant positive correlation (P < 0.01) between PIC and SOC stocks in the study area. The PIC:SOC ratio is generally greater than one over a 0–100 cm layer in the majority of croplands in the north China, with larger ratios in the salt-affected soils. Our analyses suggest that the formation and storage of PIC are regulated by levels of SOC and Ca2+/Mg2+ in soil profiles, and there is large potential for enhancing carbon sequestration as carbonate under intensive cropping through sound management in the cropland of arid, semi-arid and semi-humid regions. [ABSTRACT FROM AUTHOR]