Soil Quality Evaluation and Driving Factor Analysis of Hippophae rhamnoides Plantations in Coal Mine Reclamation Areas Based on Different Restoration Durations

The driving factors affecting soil quality were identified to evaluate the effect of vegetation on soil quality in coal mine reclamation areas with various restoration durations. This study used Hippophae rhamnoides subsp.sinensis Rousi with different reclamation durations (3, 4, 5, 6, and 7 years) in the abandoned land area of the Juxinlong coal mine in Ordos as the research subject. Artificial and abandoned grasslands were selected as the study's controls. A soil quality evaluation model was constructed to assess the soil quality in the reclamation area. A structural equation model was used to thoroughly analyze the driving factors affecting soil quality in the study area. The findings show that: (1) Reclamation duration significantly affected the physicochemical characteristics of the soil. As the reclamation duration increased, soil nutrients such as organic carbon accumulated while the bulk density index (BD) decreased. (2) The soil quality index of Hippophae rhamnoides forest land in China was the highest after 6 years of reclamation. The Hippophae rhamnoides forest land with the lowest soil quality index after 4 years of reclamation differed significantly from that after 6 years (p < 0.05). The soil quality index (SQI) of 6a (years) significantly increased by 67.44% compared to 4a. (3) By constructing a structural equation model, it was found that physical indicators (saturated water content and silt) and reclamation durations were the main drivers of soil quality. SQI had a strong interaction with organic matter (OM) and different restoration durations. The findings of this study will serve as important guidelines for future quantitative evaluation of soil quality following land reclamation and management during the ecological restoration process.