In Situ Impact of Waste Polyethylene (PE) Films on Soil Quality and Plant Growth in Agricultural Soil

Plastic films have accumulated in soil ecosystems over decades of agricultural activities. These films potentially disrupt the soil structure, hinder nutrient cycling, and deteriorate soil quality. However, there is still a substantial knowledge gap in understanding how real-world waste polyethylene films (WPEFs), with varied shapes and sizes, influence soil quality and plant performance in the fields. This study investigated the effects of WPEFs on soil quality, crop growth, and changes in plastic characteristics. In situ soil incubation was conducted for 4 months under natural field conditions, and lettuce (Lactuca sativa) was cultivated during the period. Soils with 0%–2% of WPEFs were analyzed for physicochemical and biological properties, and lettuces from each soil condition were analyzed for growth indicators after harvest. WPEFs were examined for physicochemical changes using FTIR and SEM. After the incubation, the WPEF 2.0 treatment reduced soil bulk density significantly, from 1.03 to 0.77 g/cm³, and decreased microaggregates (< 500 μm) from 22.2% to 17.2%. Meanwhile, the urease activity increased by up to 208.5% at WPEF 0.5. Although the major chemical properties remained relatively stable, lettuce growth was suppressed considerably. At WPEF 2.0, shoot height decreased by 45%, whereas total fresh and dry biomass declined by 58% and 46%, respectively. The findings suggest that the reduction in plant growth performance is driven by WPEF-induced changes in soil physical properties, particularly reduced bulk density and disrupted aggregate stability. The combined effects of soil structure and enzymatic imbalances might have contributed to the observed adverse effects on plant growth.