Influences of soil properties and hydrological processes on soil carbon dynamics in the cropland of North China Plain

Recent studies showed great variations in both soil inorganic carbon (SIC) and organic carbon (SOC) in cropland across the North China Plain. This work was designed to test the hypothesis that hydrological processes associated with the Yellow River may be responsible for the differences in soil carbon dynamics over space. We selected 22 sites from the wheat-maize cropland across the Yellow River in the south North China Plain, and measured SOC, SIC, water-extractable organic carbon (WEOC) and other soil properties over 0-20, 20-40, 40-60, 60-80 and 80 - 100 cm. Our results showed that SOC and SIC stocks were 5.82 +/- 1.26 kg C m(-2) and 13.7 +/- 8.50 kg C m(-2) in the 0 - 100 cm, respectively. SIC stock showed a positive correlation with SOC stock (P < 0.01) in pH > 7.8 soils. SOC content was lower (1.67-1.78 g kg(-1)), but WEOC:SOC ratio (4.45-5.18 %) was higher over 60 - 100 cm in the Fluvo-aquic soils near the Yellow River. Our findings indicated that low SOC content near the Yellow River may reflect weak protection of SOC, which was probably linked to hydrological processes and soil characteristics such as sand and SIC contents.