The influence of vegetation restoration on soil quality in abandoned farmlands in the Yuanjiang dry-hot valley

The Yuanjiang dry-hot valley is a typical ecologically fragile zone with intense agricultural cultivation because of its superior light and heat conditions. However, the farmlands in this zone are vulnerable to degradation because of the high rates of soil erosion. Under the Grain for Green Project, degraded farmlands were prioritised for abandonment and revegetation using both natural and artificial restoration modes. In this study, the soil quality indexes (SQIs) of 37 abandoned farmlands with different restoration times and modes were calculated using principal component analysis based on 12 soil properties in both the surface (0–15 cm) and subsurface (15–30 cm) soil layers. The results showed that the SQI values of both soil layers generally increased with restoration time, and after more than 10 years of restoration, the average SQI value (0.330) of abandoned farmlands recovered to a level similar to that of the farmland soils under continuous cultivation (0.319). Farmlands with artificial restoration (AFL; n = 14) had higher SQI values than those with natural restoration (NFL; n = 23). The degree of vegetation restoration was better under the AFL mode than the NFL mode, and had a positive effect on SQI values. All sites in the AFL mode achieved medium to good vegetation recovery, whereas 30.4 % of the sites showed poor vegetation recovery in the NFL mode. The results indicated that in the Yuanjiang dry-hot valley region, a special environment with a dry-hot climate and intensive soil erosion, artificially introducing suitable vegetation species at the early stage of abandonment had better effects on the degree of vegetation recovery, which was contributed to the increase of the SQI values of abandoned farmlands.