Long-term plastic film mulching altered soil physicochemical properties and microbial community composition in Shiyang River Basin, Northwest China

Plastic film mulching (PM) is used widely to improve crop water productivity in the arid regions of Northwest China. However, there are increasing concerns about the potential harm to soil health due to the presence of residue plastic film (RPF) mixed into the soil after long-term field mulching. In our study, we investigated the density of RPF in farmland topsoil (0 to 40 cm) (Exp. I) by analyzing 75 soil samples collected from 15 fields with varying durations of PM (ranging from 3 to 27 years). In addition, we examined the impact of long-term PM and PM + BM (BM, biodegradable film mulching) on soil health (Exp. II) based on an 8-year field experiment. The results illustrated that the weight of RPF ranged from 42.7 to 165.9 kg ha-1 after 3 to 27 years of mulching, with 10 out of 15 fields exceeded the national standard of China (75 kg ha-1). Compared with no film mulching treatment (NM), the long-term PM treatment significantly increased aggregate stability, while significantly decreased soil pH and the enzymatic activities of sucrase by 1.5 % and 33.4 %, respectively. Further, the Chao1, Shannon and Pielou's indices of bacteria significantly decreased after 8 years of PM. Compared with PM and NM, PM + BM treatment significantly improved the Chao1, Shannon and Pielou's indices of bacteria and altered the relative abundance of dominant bacterial and fungal phyla. The principal coordinates analysis (PCoA) revealed significant changes in the soil bacterial and fungal community structure under PM + BM, with the soil fungal community displaying higher sensitivity to PM + BM compared to PM. No significant differences were observed in soil organic matter (SOM), soil microbial biomass C (MBC), soil microbial biomass N (MBN) contents and the enzymatic activities of soils between PM + BM and PM treatments. Overall, BM could be a promising alternative to polyethylene plastic film for improving soil health and is recommended for farming practice in the arid regions of Northwest China.