Consequences of 33 Years of Plastic Film Mulching and Nitrogen Fertilization on Maize Growth and Soil Quality

Plastic film mulching and urea nitrogen fertilization are widely used in agricultural ecosystems, but both their long-term use may leave a negative legacy on crop growth, due to deleterious effects of plastic and microplastic accumulation and acidification in soil, respectively. Here, we stopped covering soil with a plastic film in an experimental site that was previously covered for 33 years and compared soil properties and subsequent maize growth and yield between plots that were previously and never covered with the plastic film. Soil moisture was about 5-16% higher at the previously mulched plot than at the never-mulched plot, but NO₃^- content was lower for the former when with fertilization. Maize growth and yield were generally similar between previously and never-mulched plots. Maize had an earlier dough stage (6-10 days) in previously mulched compared to never-mulched plots. Although plastic film mulching did add substantial amounts of film residues and microplastic accumulation into soils, it did not leave a net negative legacy (given the positive effects of the mulching practice in the first place) for soil quality and subsequent maize growth and yield, at least as an initial effect in our experiment. Long-term urea fertilization resulted in a pH decrease of about 1 unit, which bring a temporary maize P deficiency occurring in early stages of growth. Our data add long-term information on this important form of plastic pollution in agricultural systems.