The effects of land use and landscape position on labile organic carbon and carbon management index in red soil hilly region, southern China

Labile organic carbon (LOC) and carbon management index (CMI), which are sensitive factors to the changes of environment, can improve evaluating the effect of land management practices changes on soil quality. The objective of this study was to investigate the effects of land use types and landscape positions on soil quality as a function of LOC and CMI. A field study in a small watershed in the red soil hilly region of southern China was conducted, and soil samples were collected from four typical lands (pine forest (PF) on slope land, barren hill (BH) on slope land, citrus orchard (CO) on terrace land and Cinnarnornum Camphora (CC) on terrace land) at a sampling depth of 20 cm. Soil nutrients, soil organic carbon (SOC), LOC and CMI were measured. Results showed that the LOC and CMI correlated to not only soil carbon but also soil nutrients, and the values of LOC and CMI in different land use types followed the order CC > PF > CO > BH at the upper-slope, while CO > CC > BH > PF at mid-slope and down-slope. With respect to slope positions, the values of LOC and CMI in all the lands were followed the order: upper-slope > down-slope > mid-slope. As whole, the mean values of LOC and CMI in different lands followed the order CC > CO > PF > BH. High CMI and LOC content were found in the terrace lands with broadleaf vegetations. These results indicated that the terracing and appropriate vegetations can increase the carbon input and lability and decrease soil erosion. However, the carbon pools and CMI in these lands were significantly lower than that in reference site. This suggested that it may require a long time for the soil to return to a high-quality. Consequently, it is an efficient way to adopt the measures of terracing and appropriate vegetations planting in improving the content of LOC and CMI and controlling water and soil loss in fragile ecosystems.