In the vast cotton fields of Xinjiang, plastic film covering technology has been a weapon for increasing yield—it conserves water, raises temperatures, and improves water utilization efficiency, significantly boosting cotton production in arid regions. However, on the flip side, these non-degradable plastic films accumulate in the soil year after year, and the microplastics formed from their fragmentation are quietly threatening soil health and ecological safety. How does residual plastic film evolve into microplastics under long-term plastic mulching? Is this process linear?
Recently, Associate Professor Can Hu from Tarim University and Researcher Haichun Zhang from the Xinjiang Academy of Agricultural Sciences provided key answers through a study on cotton fields with 5–30 years of mulching. The article was published in the journal Frontiers of Agricultural Science and Engineering, Volume 13, Issue 1 (DOI: 10.15302/J-FASE-2025627).
The research team conducted experiments in typical arid cotton fields in Aral City, Xinjiang, systematically analyzing the dynamic changes of residual film and microplastics in the soil over different durations. The results showed that as the mulching time increased, the amount of residual film continued to rise: the residual film amount in fields mulched for 5 years was 46 kg·ha^–1, which surged to 281 kg·ha^–1 after 30 years. Notably, the topsoil (0–10 cm) was the primary accumulation zone, while the amount of residual film in deeper soil (20–30 cm) also began to accelerate after 20 years.
More importantly, the transformation relationship between residual film and microplastics was highlighted. The study found a significant positive correlation between the number of microplastics and the amount of residual film, indicating that residual film is a major source of microplastics. However, this transformation is not entirely linear—when the amount of residual film exceeds 160–200 kg·ha^–1, the rate of microplastic generation suddenly accelerates by 85%, akin to pressing an accelerator button. This phenomenon is referred to as the threshold effect, where high residual film amounts trigger more intense fragmentation of plastic and the release of microplastics.
The trend of microplastics becoming finer is also evident. In the topsoil of cotton fields mulched for 5 years, microplastics smaller than 1 mm accounted for only 7.9%, while this proportion rose to 22.6% after 30 years; conversely, the proportion of microplastics larger than 2 mm dropped from 49.2% to 13.8%. This indicates that long-term mulching not only increases the quantity of microplastics but also reduces their size, making them more likely to migrate downward through soil pores and affect deeper soil environments.
Based on 30 years of field trial data, this study systematically quantified the contribution of residual film to microplastic generation. By refining microplastic size classification, it revealed the dynamic distribution of fragments of different sizes over time and soil depth. More importantly, it clarified the critical threshold of 160–200 kg·ha^–1—when the amount of residual film exceeds this value, microplastic pollution enters an acceleration phase.
The study emphasizes that timely removal of residual film and preventing its accumulation beyond the threshold of 160–200 kg·ha^–1 is key to reducing microplastic pollution. Currently, the issue of residual film pollution in cotton fields has garnered widespread attention, and the results of this research will provide scientific support for formulating more precise residual film recovery strategies and optimizing mulching technology, aiding the sustainable development of agricultural ecosystems in arid regions.
DOI: 10.15302/J-FASE-2025627