Purpose

The ecological damage caused by cut slopes in mountainous areas is serious, and ecological restoration is urgently needed. In this context, outside soil spray seeding (OSSS) combined with a frame beam is often used in mountainous areas of southwestern China. The aims of this study were (1) to determine the differences in soil organic carbon (SOC) and its fractions of cut slopes under different restoration methods and (2) to explore the factors influencing SOC and its fractions of cut slopes in this study area.

Materials and methods

Two cut slopes restored by different restoration methods (framed slope, using OSSS combined with a frame beam, FS; rimless slope, unassisted restoration, RS) were selected, and a nearby naturally developed slope that had not been cut was used as a reference (NS). The SOC, SOC fractions, and related soil parameters were investigated.

Results and discussion

Compared with RS, the available phosphorus, urease activity, amylase activity, microbial biomass carbon (MBC), and light-fraction organic carbon (LFOC) levels of FS were significantly higher. However, there were no significant differences in pH, bulk density, available nitrogen, saccharase activity, SOC, particulate organic carbon (POC), and readily oxidizable organic carbon (ROC) between FS and RS. Notably, the MBC contents of FS and RS were higher compared to that of NS, which may be due to the fact that the deep soil was exposed to the air after stripping the surface soil of the cut slopes, which facilitated the growth of aerobic microorganisms. The dissolved organic carbon (DOC) content of FS was lower than that of RS, most likely because of the higher MBC content of FS compared with RS. The main soil parameters influencing soil SOC and its fractions were available nitrogen, available phosphorus, and bulk density.

Conclusions

Despite the implementation of ecological restoration measures, the SOC and its fractions of the cut slope did not fully recover, and there was a gap between the soil quality of FS and NS. Further research is needed to determine whether OSSS combined with frame beams is an effective ecological restoration method for cut slopes in this area.