Long-term biodegradable mulch films application in agricultural fields: effects on soil functionality and microplastic generation

The accumulation of microplastics (MPs) in agricultural soils has become a growing environmental concern, particularly due to the use of plastic mulch films. Biodegradable mulch films (BMFs) have been proposed as a sustainable alternative, yet long-term field evidence remains scarce. In this study, we evaluated MPs occurrence and soil functionality in two commercial farms in northern Italy where BMFs have been applied for over a decade. Soil samples were collected from plots with and without mulch, MPs (25 μm-5 mm) were isolated and chemically characterized, and soil biochemical parameters were assessed. The results revealed a diverse composition of plastics mainly not related to agricultural practices, suggesting external inputs from diffuse sources such as atmospheric deposition or irrigation water. Overall, MPs concentration over the two fields ranged between 300 and 580 MP items kg with control surrounding areas reaching >1000 MP items kg. Notably, among the fragments spectrally compatible with biodegradable materials, their origin could not be directly linked to the applied mulch films and are therefore presumed to originate from external sources. From a biochemical point of view, BMFs application enhanced, on average, microbial biomass carbon (+27 %) and enzymatic activity (+23 % for β-glu, +13 % for β-xyl, and +31 % for PME), although these effects were strongly site-specific, with soil type emerging as the main driver of variability. Overall, our findings indicate that long-term use of BMFs does not lead to clear MP accumulation within the assessed size range nor adversely affect soil functionality, supporting their potential as an environmentally compatible alternative to conventional polyethylene mulches. Further research is nevertheless required to better understand their long-term transformation and environmental fate under field conditions.