Calcium carbonate promotes the formation and stability of soil macroaggregates in mining areas of China

We studied changes in the concentrations of aggregate-cementing agents after different reclamation times and with different fertilization regimes, as well as the formation mechanism of aggregates in reclaimed soil, to provide a theoretical basis for rapid reclamation of soil fertility in the subsidence area of coal mines in Shanxi Province, China. In this study, soil samples of 0–20 cm depth were collected from four fertilization treatments of a long-term experiment started in 2008: no fertilizer (CK), inorganic fertilizer (NPK), chicken manure compost (M), and 50% inorganic fertilizer plus 50% chicken manure compost (MNPK). The concentrations of cementing agents and changes in soil aggregate size distribution and stability were analysed. The results showed that the formation of >2 mm aggregates, the aggregate mean weight diameter (MWD), and the proportion of >0.25 mm water-stable aggregates (WR0.25) increased significantly after 6 and 11 years of reclamation. The concentration of organic cementing agents tended to increase with reclamation time, whereas free iron oxide (Fed) and free aluminium oxide (Ald) concentrations initially increased but then decreased. In general, the MNPK treatment significantly increased the concentrations of organic cementing agents and CaCO3, and CaCO3 increased by 60.4% at 11 years after reclamation. Additionally, CaCO3 had the greatest effect on the stability of aggregates, promoting the formation of >0.25 mm aggregates and accounting for 54.4% of the variance in the proportion and stability of the aggregates. It was concluded that long-term reclamation is beneficial for improving soil structure. The MNPK treatment was the most effective measure for increasing maize grain yield and concentration of organic cementing agents and CaCO3.