Microplastics in agricultural soils have become the research hotspot in recent years, however, the quantitative methods based on the traditional visual inspection may have a high false detection rate. Here we combined the laser direct infrared (LDIR) and Fourier–transform infrared (FTIR) methods to investigate the microplastics in farmland with long–term agricultural activities. The results showed that the total abundance of microplastics reached 1.98 ± 0.41 × 10⁵, 1.57 ± 0.28 × 10⁵, 1.78 ± 0.27 × 10⁵, and 3.20 ± 0.41 × 10⁵ particles/kg soil in cotton fields with film mulching of 5, 10, 20, and >30 years, respectively. LDIR results indicated that microplastics ranging from 10 to 500 μm accounted for 96.5–99.9 % of the total microplastic amounts in the soils. Additionally, a total of 26 polymer types of microplastics were detected, among which polyethylene (PE), polypropylene (PP), polyvinyl chloride (PVC), polyamide (PA), and polytetrafluoroethylene (PTFE) were dominantly observed. For the microplastics detected by FTIR (500 μm–5 mm), PE polymer was majorly observed (88.0–98.9 %). Most microplastics were films (88.2 %), while fibers and pellets were also found. The reclaimed water from sewage treatment plants, the drip irrigation utilities, and the residual plastic film are the potential sources of microplastics in the farmland soils. By using the automated quantitative and identifiable approaches, this study suggested that the commonly used visual counting method may underestimate the microplastic contamination in agricultural soils.

近年来，农业土壤中的微塑料已成为研究热点，但基于传统目测的定量方法可能存在较高的误检率。在这里，我们结合了激光直接红外 (LDIR) 和傅里叶变换红外 (FTIR) 方法来研究具有长期农业活动的农田中的微塑料。结果表明，微塑料总丰度达到1.98±0.41×10 ⁵、1.57±0.28×10 ⁵、1.78±0.27×10 ⁵和3.20±0.41×10 ⁵分别覆盖 5、10、20 和 >30 年的棉田颗粒/千克土壤。LDIR 结果表明，10 至 500 μm 的微塑料占土壤中微塑料总量的 96.5-99.9%。此外，共检测到 26 种聚合物微塑料，其中以聚乙烯 (PE)、聚丙烯 (PP)、聚氯乙烯 (PVC)、聚酰胺 (PA) 和聚四氟乙烯 (PTFE) 为主。对于 FTIR (500 μm–5 mm) 检测到的微塑料，主要观察到 PE 聚合物 (88.0–98.9 %)。大多数微塑料是薄膜（88.2%），同时也发现了纤维和颗粒。污水处理厂的再生水、滴灌设施和残留的塑料薄膜是农田土壤中微塑料的潜在来源。