Long-Term Observation of Field Application of Reclaimed Mine Substrates by Ryegrass–AMF–Sludge Combination: Key Factors of Organic Carbon Accumulation

Abstract

The effects of planting ryegrass combined with sludge addition and arbuscular mycorrhizal fungi (AMF) inoculation on organic carbon accumulation in reclaimed mine substrates (RMS) were investigated. A 6-year field experiment was carried out; in the 0–15-cm edaphic layer, a mixed matrix was constructed according to the ratio of fly ash to coal gangue to sludge=1∶6∶3, with 0.5 kg/m2 of AMF inoculated and ryegrass sowed annually. The particle size, carbon fraction, enzyme activity, AMF-related protein and ryegrass rhizosphere effect of RMS aggregates were monitored regularly. The cumulative contribution of the above factors to organic carbon in RMS was quantitatively explored by path analysis. After reclamation, the texture of reclamation matrix in mining area was improved, the stability of aggregates augmented significantly with the proportion of large aggregates increased gradually. Organic carbon in RMS increased by 1.96 times to 38.12 g/kg; the contents of total N and available P increased significantly year by year, mainly concentrated in aggregates. Path analysis showed that the underground biomass of ryegrass and 0.5–2-mm aggregates were the two factors with the strongest direct positive effect on organic carbon accumulation in RMS. In addition, available phosphatase and easily extractable glomalin affected the process through complex interaction with each other. A combination of ryegrass-AMF-sludge on a reclamation mining field could improve the quality of RMS through aggregates by promoting the process of soil formation, and ryegrass root growth conducive to organic carbon accumulation.