Effects of Different Reclamation Methods on Soil Aggregate Cementing Agents and Potential Aggregate Formation Mechanisms

Iron ore tailings have been shown to promote the formation of soil aggregate cementing agents through weathering, thereby influencing soil aggregate formation in reclaimed land. However, their mechanism of action under different reclamation methods remains unclear. This study established a field station in the semi-arid region of Northern China to investigate three typical iron ore tailing reclamation methods, including topsoil blending type (DT), sublayer moisture conservation type (JT), and thick-layer tailings type (FT), with adjacent farmland as the control (CK). The analysis of soil organic carbon (SOC) components, soil inorganic carbon (SIC), iron/aluminum oxides, and aggregate composition and stability in the reclaimed soils revealed the evolution patterns of cementing materials and the potential mechanisms driving aggregate formation. The results indicate that the reclamation process promotes the weathering of tailings, with a significant increase in free iron oxide (Fed) content ranging from 19.09% to 41.93%. Iron oxides released from iron ore tailings influenced the reclaimed topsoil through plant litter return processes, resulting in a significantly higher amorphous iron oxide (Feo) content compared to CK. Additionally, the content of crystalline aluminum oxide (Alc) in the DT topsoil showed a significant increase, reaching 2.82 g/kg. The variation in organic and inorganic cementing agents significantly influences aggregate composition and stability, with soil particulate organic carbon (POC), crystalline iron oxide (Fec), Alc, and amorphous aluminum oxide (Alo) identified as the primary agents affecting aggregate formation (p < 0.05). After five years of reclamation, the proportion of DT macroaggregates (>0.25 mm) increased to 42.10%, and both the mean weight diameter (MWD) and the geometric mean diameter (GMD) increased significantly to 2.21 mm and 0.43 mm, respectively. In contrast, JT macroaggregates and microaggregates (0.053–0.25 mm) decreased to 26.88% and 29.01%, respectively, and aggregate stability significantly declined. FT macroaggregates and their stability showed no significant difference compared to CK. The study shows that after years of reclamation, both DT and FT reclamation methods have reached normal farmland levels in terms of aggregate formation and stability, making them practical and valuable reclamation solutions.