Inferring irrigation regimes and sunshine duration from the distribution and spectral characteristics of farmland...

Both anthropogenic and natural processes influence the fate of microplastics (MPs), yet whether MPs can preserve identifiable signatures of these influences remains underexplored. This study evaluated whether the vertical distribution and infrared spectral characteristics of farmland MPs are associated with irrigation hydraulic processes and climatic factors. MPs were extracted and characterized from soil collected at different depths (0-100 cm), and the relationships between the vertical distribution and spectral variability of MPs and environmental variables, including sunshine duration and air temperature, were analyzed. We observed that MP abundance declined markedly with depth, from 8008 ± 2765.57 items kg^-1 at 0 cm to 996 ± 505.34 items kg^-1 at 100 cm, while polyethylene was the dominant polymer type (52.87%). A significant correlation was identified between the unsaturated vinyl band at 900 cm^-1 and sunshine duration, suggesting that the spectral features of MPs may preserve signals related to sunshine duration. Theoretical analysis suggested that the distribution patterns of MPs in farmland may differ among irrigation regimes, implying that the vertical distribution of MPs may provide diagnostic clues to irrigation hydraulic processes. No significant association was observed between MP infrared spectral features and mean air temperature in this study. These findings suggest that MPs in farmland soils may serve as potential archives of environmental and management-related information.