Characteristics of soil organic carbon fractions under different land use patterns in a tropical area

Purpose To explore the effects of land use patterns on the accumulation of soil organic carbon (SOC) fractions in tropical areas, soil samples from paddy fields, abandoned croplands and vegetable-growing lands were collected at depths of 0-10, 10-20 and 20-30 cm in Hainan province, China. Methods The particulate organic carbon (POC) and mineral-associated organic carbon (MOC) concentrations in soil samples were determined, and their distribution characteristics were analysed. Results The results showed that MOC is the main component of SOC, with an average MOC/SOC ratio of 0.65. The POC and MOC concentrations showed a trend of paddy field > abandoned cropland > vegetable-growing land and gradually decreased with an increase in soil depth. The POC concentrations in the 0-10-cm soil of the paddy field and abandoned cropland were significantly higher than those of the 20-30-cm layers, and the MOC concentration in the 0-10-cm soil layer of the paddy field was significantly higher than that of the 10-20 and 20-30 cm layers. Correlation analysis showed that POC and MOC had a significant positive correlation with SOC, a significant negative correlation with soil particulate diameter and a weak correlation with pH and Eh. Conclusions Therefore, soil tillage and fertilisation under different land use patterns have a great influence on organic carbon fractions, and paddy fields have high carbon sequestration potential.