Macroplastic Properties and Distribution Influenced by Field Managements with a Long-Term Plastic-Film-Mulching in Mollisols of Northeast China

Abstract

Plastic-film-mulching (PFM) has been widely used for improving the soil moisture and temperature in the farmland, while most of them are degraded into macroplastic (MaP) in soils and cause negative effects on biota. However, it is still not clear how field management, such as tillage frequency and fertilization, influences MaP in soils. In this study, MaP was investigated at 0-20 cm and 20-30 cm soil depths in three vegetable fields (5.2 ha, 6.5 ha, and 3.4 ha) with different management methods (MM) after thirteen years’ PFM in Mollisols of Northeast China. The MM2 has the highest tillage frequency, followed by MM1 and MM3. The total fertilization after transforming into chemical fertilizers was MM1> MM2>MM3. The results showed that (1) Polyethylene (PE), polypropylene (PP), polystyrene (PS), polyethylene terephthalate (PET) were the top frequently occurring MaP, melamine-formaldehyde resin (MF) and Poly (ether urethane) (PEUR) were also found. (2) PE-MaP (>87%) was the predominant MaP type mainly coming from PFM, and field cultivation increased the chances of MaP coming from the outside field. (3) Abundance, mass and accumulated areas of MaP significantly decreased from 0-20 cm to 20-30 cm soil layer, and were mainly influenced by the tillage practice. (4) MM2 has the highest abundance of MaP with size < 4 cm2, while MM3 has the highest abundance at the size of 4-16 cm2 and >16 cm2. (5) Compared with the original plastics, new function groups appeared on the surface of PE, PP, PS and PET, and both the higher fertilization and tillage frequency increased the chances of MaP oxidation. Generally, compared with low fertilization and tillage frequency, both high fertilization and high tillage frequency increased degradation of MaP, decreased negative effects of MaP sizes on crop growth, while produced more hazardous substances.