Vegetation and soil nutrient restoration of cut slopes using outside soil spray seeding in the plateau region of southwestern China

Outside soil spray seeding (OSSS) is used widely for road cut revegetation, and the artificial soil used in OSSS can improve slope soil conditions and nutrients, and help promote plant growth and succession. Three different slopes was investigated to evaluate the effectiveness of OSSS for restoration, including a natural slope (NS), a cut slope without any artificial recovery treatment (CSW) and a cut slope treated with OSSS (CSO). The recovery of cut slopes was determined by evaluating a number of factors, including indices associated with plants on the slopes, soil enzyme activities (urease and sucrase), and soil nutrient content (soil organic matter (SOM), total phosphorous (TP), total potassium (TK), available nitrogen (AN), available phosphorous (AP), available potassium (AK), potassium (K+), calcium (Ca2+), magnesium (Mg2+), and sulphate (SO42−)). The results indicated that the vegetation and soil conditions differed between the three slopes. The Shannon-Wiener index (H), the Simpson index (D), and the Margalef index (R) values from the CSO and NS were lower than those of the CSW, whilst the Pielou index (E) value and vegetation canopy cover were higher for the CSO and NS than for the CSW. The content of SOM and AN in soil from the CSO was lower than in soil from the NS and CSW, and content of many nutrients were higher in soil from the CSO than in soil from the NS and CSW. This suggests that the restoration of vegetation and soil nutrients on the CSO was relatively successful. Our results indicated that the use of OSSS to restore cut slopes is effective in plateau areas. However, despite improvements in soil nutrient levels, there were still nutritional imbalances. Therefore, more attention should be paid to balancing nutrients in the later stage of OSSS implementation for the recovery of cut slopes at high altitudes.