Plastic film residues on cropland: monitoring soil contamination through optical remote sensing

Abstract. Plastic films have been improving agricultural production and covering an increasing surface area of cropland in the last decades. Yet their use has been connected to the generation of plastic residues, potentially acting as a main secondary microplastic source in agricultural soils. Monitoring the generation of plastic film residues is crucial for identifying good management practices and assessing the risk of plastic use in agriculture. Remote sensing has been qualified as a valuable tool for monitoring macroplastic mainly on waters, while its use on agricultural soils is mostly unexplored. Our study combined proximal and remote sensing techniques to lay the foundations of UAV (Unmanned Aerial Vehicle) use for monitoring macroplastic film residues on cropland. Through proximal and UAV acquisitions of five-bands multispectral data (i.e., blue, green, red, red edge, near infrared), we highlighted the potential of off-the-shelf miniaturised sensors and identified possible workflows for detecting macroplastic film residues. Our findings highlight a greater efficacy of spatial resolution over spectral resolution, encouraging the use of high-resolution RGB cameras over multispectral cameras. Through proximal acquisitions of hyperspectral data, we built spectral libraries and located absorption peaks for the most commonly used plastic films. We highlighted that these absorption peaks unambiguously identify plastic films on cropland and offer the potential to distinguish plastic types, encouraging the development of sensors tailored for plastic detection.