Plasticulture: Product- and polymer-specific weathering shapes microplastic accumulation and composition in agricultural soils.

Agricultural plastic use introduces a diverse range of polymeric residues into soils. Yet, how product- and polymer-specific weathering processes govern microplastics (MPs) accumulation and compositional transitions over time remains poorly resolved. Most field assessments focus primarily on mulch films and attribute MP buildup mainly to the duration of use rather than material-specific degradation dynamics. Here, we combine field-scale statistical modelling with controlled UV aging experiments to evaluate how polymer chemistry and product design, particularly thickness, regulate MP generation in intensively managed agricultural soils. Results revealed that MP abundance increased progressively with mulching duration, with long-term fields (>20 years) exhibiting more than 5-fold higher abundances (5571 ± 2747 particles kg-1) than non-mulched fields (1174 ± 454 particles kg-1). Polymer composition shifted from polypropylene (PP) dominance in short-term systems to greater polyethylene prevalence over prolonged mulching. Fields utilizing PP support threads alongside mulch films had ∼1.9-fold higher MP loads (2886 ± 776 particles kg-1) than mulch-only systems (1489 ± 563 particles kg-1) at comparable durations (1-5 years). Negative binomial GLM confirmed that auxiliary plastics (threads) independently amplify soil MP loads. Further, laboratory aging revealed polymer-dependent degradation hierarchies. Crack network analysis showed that thinner films (3734 mm-2) develop higher crack density and are more prone to fragmentation than thicker films (2693-3004 mm-2). Risk assessment showed high to very high PLI in long-term mulched and thread utilizing systems, while PHI varied independently of MP abundance, reflecting polymer-driven hazard. Overall, the results suggest that polymer- and product-specific weathering susceptibility influences soil MP accumulation and should be explicitly incorporated into agricultural plastic management policies and mitigation strategies.