Long-term recovery of compacted reclaimed farmland soil in coal mining subsidence area

Abstract

During the reclamation process of coal mining subsidence areas, mechanical compaction hinders the rapid recovery of reclaimed mine soil (RMS) functions to their pre-mining levels. To optimize reclaimed farmland management, which can promote the recovery of compacted soils, this study aims to explore the key factors and underlying mechanisms affecting RMS recovery from a systemic perspective using complex network theory (CNT). Soil samples from reclaimed farmland at different recovery stages (0, 2, 6, 12, 16, and 22 years) and adjacent non-subsided cultivated soils (NCS) were collected at a depth of 0 ∼ 20 cm in the eastern plains mining region of China. Twenty-four soil indicators were measured, and their evolution over RMS recovery was analyzed. CNT was employed to systematically analyze the complex network relationships among these indicators, identifying key factors and underlying mechanisms affecting RMS recovery. The results indicated that compaction led to soil macroaggregate (MA) destruction, mineralization losses of organic carbon and nitrogen, reduced microbial activity, degraded soil fertility, and increased complexity and disorder in the relationships among soil indicators. Re-cultivation had a positive effect on the recovery of RMS. After 22 years of cultivation, significant improvements in soil structure were observed, with MA increasing by 30.95 % (P < 0.05). Based on this, organic carbon gradually accumulated, with soil organic carbon (SOC) increasing by 250.94 % (P < 0.05). Microbial abundance similarly improved, with total microbial biomass (TB) increasing by 123.07 % (P < 0.05). Soil fertility was also enhanced, with alkali-hydrolyzed nitrogen (AN), available phosphorus (AP), and available potassium (AK) increasing by 125.96 %, 304.84 %, and 61.90 %, respectively. However, RMS indicators and system structure remained distinct from those of the NCS. The first approximately 12 years after re-cultivation represented a critical period during which soil structure improvements drove RMS functional recovery, with a focus on MA recovery. Increasing particulate organic carbon (POC) accumulation is an effective strategy to promote aggregation in compacted RMS. Microbially mediated carbon–nitrogen cycling emerged as a crucial driver of the gradual recovery of the RMS system after re-cultivation.