Semi-quantitative analysis of agricultural plastic mulch in paddy soils based on ATR-IR

The extensive utilization of plastic mulch films results in the accumulation of microplastics in agricultural soils, thereby posing significant environmental and agricultural risks. This study investigated the semi-quantitative detection of residual fragments of mulch films in paddy soils by ATR-IR. The polyethylene (PE) film fragments in paddy soils were identified. Characteristic IR absorption bands at 1463, 1473, 2847, and 2912 cm^-1 were considered as reliable indicators for the identification. In addition, clean soil samples (before mulching) were mixed with different abundances of PE microplastics to establish calibration curves. Calibration curves achieved the lowest RMSE of 0.16 wt.% and the highest R² of 0.98. Based on (1463 + 1473)/997 cm^-1, the low error (p ≥ 0.05) of the ratios indicated relatively high accuracy. It also demonstrated that PE microplastic content in the humid paddy field was higher than that in the dry paddy field. The higher moisture in humid paddy soils hence hold more residual microplastics. This research provided valuable insights for improving the management of agricultural plastic mulch in paddy systems.