Soil structure shifts with earthworms under different organic fertilization in salt-affected soils

Earthworm incubation combined with organic fertilization is promoted as an amended measure to improve soil properties in the ecological restoration of various degraded soils. However, the impacts of earthworms on the soil aggregate size under different organic fertilization in salt-affected soils have not yet been fully revealed. This hinders our ability to develop policies by which to alleviate soil salinization. In this study, under mesocosm experiments, we investigate the effects of earthworm (Aporrectodea trapezoides) and organic fertilization on the soil aggregate size after 16 weeks of incubation. The soil treated with clover residues showed lower earthworm survival rates and biomass compared to that treated with sheep manure. However, the soil macropores and large macroaggregate were higher in the soils treated with clover residue when earthworms were present. In addition, earthworm burrowing activities form pathways toward food patches improve the characteristics of soil macropores, and the properties of the residue itself play a decisive role. Moreover, whether earthworms are present or not significantly influences the soil macroporosity, macropore number, and soil electrical conductivity. This demonstrates that earthworms exhibit a key feature of soil physical functioning in salt-affected soil. In conclusion, we propose that the application of earthworms with organic residues in salt-affected soils is a priority in producing and maintaining favorable soil structure.