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National-scale mapping of plastic-mulched farmlands in China based on deep semantic segmentation and Sentinel-2 imagery
Summary
Scientists used AI and satellite images to create the first detailed map of where China uses plastic sheeting (called "mulch film") to help crops grow — covering about 6 million hectares of farmland, mostly in the drier western regions. This matters because these plastic films break down into microplastics that build up in soil over time, potentially entering the food we eat and the water we drink, so knowing exactly where this farming practice is most concentrated helps target cleanup and pollution-reduction efforts where they're needed most.
Plastic mulching films are widely utilized in agriculture around the globe to increase soil temperature, retain soil moisture, and prevent pests. However, its large-scale and long-term application causes several environmental issues, including soil microplastic accumulation and “white pollution”. Therefore, obtaining reliable spatial distribution data on plastic-mulched farmlands (PMFs) is essential, particularly at a large scale. This study aimed to provide the first national-scale PMFs map of China with a high resolution of 10 m. Specifically, this study proposed a hybrid framework for PMFs mapping, which employed the Vision Mamba UNet (VM-UNet) semantic segmentation model for both updating weak labels and national-scale PMFs mapping. First, a web crawler was used to gather news and academic literature related to China's PMFs, extracting temporal and spatial distribution data on plastic mulch films. Afterwards, a national 1° grid system was established for data organization, where initial weak labels were generated via Google Earth Engine and Sentinel-2 imagery. These labels were subsequently refined through an active learning strategy within a transfer learning framework. Finally, VM-UNet was adopted for the national-scale prediction of China's plastic-mulched farmland. Experimental results demonstrate that China-PMF-10 dataset achieved a user's and producer's accuracies of 85.90 ± 1.25% and 78.48 ± 5.37% for PMFs, respectively. China's total PMFs area in 2020 was estimated at approximately 6.06 ± 0.42 Mha (95% CI). Furthermore, statistical significance testing confirmed that the Hu Line emerged as a critical boundary, with more extensive PMFs and higher PMFs-to-cropland ratios to its west. This study provides a scientific basis for sustainable agricultural management and plastic pollution mitigation in China, and offers methodological insights for large-scale PMFs monitoring in other regions.