Microplastic Accumulation and Soil Quality Changes Under Varying Plastic Mulching Durations in the Mediterranean Region

Abstract Research on microplastics (MPs) in soils has been widespread, but their impact on soil quality and the effects of mulching duration are still unclear. Therefore, the aim of this study is to determine how MP accumulation in mulched agricultural soils affects soil quality across three different mulching durations. Soil samples were collected from two depths (0–10 and 10–20 cm) at 15 agricultural sites in Adana, Türkiye, representing mulching durations of 5, 10, and 30 years. Microplastics were extracted using density separation and identified with ATR-FTIR. Soil physical, chemical, and biological properties were analyzed, and Soil Quality Index (SQI) was assessed with the Soil Management Assessment Framework (SMAF), which considers soil taxonomy, climate class, slope, sampling time, texture, mineralogy, organic matter, and analytical techniques to estimate the functional potential of each soil, considering the relevant soil indicators under MP accumulation. In this study, the evaluated soil indicators included physical properties such as bulk density (BD), aggregate stability (AS), available water content (AWC), and water-filled pore space (WFPS); chemical properties such as soil pH, electrical conductivity (EC), available phosphorus (P), and exchangeable potassium (K); and biological properties such as soil organic carbon (SOC), microbial biomass carbon (MBC), and potentially mineralizable nitrogen (PMN). Our data showed clear differences in both MPs and SQI across the three mulching periods, allowing the observed patterns to be better understood. The results showed that prolonged mulch application substantially increased MP accumulation and negatively affected key physical and biological soil indicators. Long-term mulching consistently reduced SQI values, indicating a cumulative decline in soil health and ecosystem functioning. At 0–10 cm depth, MP abundances were 69.3 ± 18.2, 64.0 ± 14.39, and 48.0 ± 9.53 particles kg − 1 for short-, medium-, and long-term durations, respectively, while at 10–20 cm depth, the values were 37.33 ± 6.18, 48.0 ± 9.75, and 78.66 ± 27.76 particles kg − 1 . These depth-specific patterns were accompanied by increases in bulk density (10%), substantial reductions in aggregate stability (48%), nitrogen mineralization (24%), and microbial biomass carbon (14%) with increasing plastic use (from S to L) at 0–10 cm depth. Overall, these analytical outcomes corresponded with a 17% reduction in SQI under long-term mulch application. These findings provide a solid foundation for predicting and monitoring MP contamination in agricultural soils with different mulch durations. The main limitation of this study is that, as a field-based investigation conducted under real agricultural conditions, it lacks full control over environmental and management variability, which should be considered when interpreting the results.