Evaluation of soil quality in different succession periods of abandoned tillage in the agro-pastoral interlaced area at the northern foot of the Yinshan Mountains

This study used the method of substituting time with space, analyzing soil physicochemical properties between abandoned croplands (5, 15 and 20 years) and farmland in the desert and typical grassland in the Northern Piedmont of Yinshan Mountain, Inner Mongolia. Natural grassland was used as a control. Soil quality was evaluated using principal component analysis. Results showed the following: with increased duration since abandonment, soil water content, saturated hydraulic conductivity, capillary porosity, non-capillary porosity, soil organic carbon, total phosphorus and available phosphorus increased; soil bulk density, the content of nitrate-nitrogen, ammonium-nitrogen and total nitrogen gradually decreased with increased duration since abandonment; maximum water holding capacity increased in desert grassland and decreased in typical grassland; capillary water holding capacity and field water holding capacity did not change significantly. As the duration of recovery increased, soil pH of desert grassland soils decreased but increased in typical grassland soils. Statistical analyses demonstrated that soil organic carbon, non-capillary porosity, bulk density, and total nitrogen were the main factors affecting desert grassland soil quality. Natural grassland had the highest soil quality, followed by abandoned croplands for 5 years, 15 years, and 20 years, and farmland. Organic carbon, pH, bulk density, and saturated hydraulic conductivity were the main factors influencing soil quality in typical grasslands and the typical grassland comprehensive score was as follows: natural grassland > abandoned croplands for 15 years > abandoned croplands for 20 years > abandoned croplands for 5 years > farmland. In desert grassland samples, soil quality of farmland and abandoned land were lower than the average soil quality, while the soil quality scores of abandoned croplands for 15 years, and 20 years, and natural grassland, were higher than the average soil quality in the typical grassland samples. Therefore, passive restoration (without any intervention) is proposed as an effective strategy for grassland restoration in abandoned croplands. The results of our study indicate that 20 years is sufficient time to restore crops in typical steppes, but more time may be needed in desert steppes. For abandoned land, we must develop different strategies for restoring soil quality for desert grasslands and typical grasslands.