Twenty-One Years of Plastic Mulching on Blueberries: Content of Microplastics and Effects on Soil Properties

Plastic use has increased substantially worldwide owing to its benefits for food production. However, they are a source of microplastics (MPs) and their presence can affect soil properties. The objective of this study was to assess whether the length of blueberry orchards in the presence of plastic mulching is related to different MPs contents and to elucidate whether the presence of MPs is related to changes in soil chemical and microbiological properties. Four blueberry orchards with 6-, 11-, 16, and 21 years of plastic mulch were evaluated. Soil was sampled once at 0-10 cm depth, and the content of MPs, soil properties related to soil fertility, and soil microbial activity were measured. The 21-year-old orchard was associated with an increase in soil organic matter, pH, basal soil respiration, urease, beta-glucosidase, and acid phosphatase activities compared to the other orchards. However, available N and P levels were significantly higher in the 16-year-old field, whereas dehydrogenase activity was higher in the 6-year-old field. For MPs content, the 16- and 21-year-old fields presented higher accumulation of MPs in the soil at 256 and 112 items kg-1, respectively, which was negatively associated with chemical properties, such as N, P, and K, and an increase in pH. This may be a response to differences in biological properties, such as soil enzymatic activity. This study revealed the process by which MPs accumulated in the soil, specifically in relation to the duration of mulch use and the effects of soil properties.