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Soil erosion molds soil properties and the uneven distribution of microplastics in navel orange orchards on slopes
Summary
A field study of navel orange orchards on slopes in China found that soil erosion redistributes microplastics unevenly, concentrating them in depositional zones while also altering soil nutrients and structure. This work reveals that erosion is not just a soil degradation problem but also a mechanism that spreads microplastic pollution across agricultural landscapes.
Soil erosion led to soil properties and microplastic distribution variations, further aggravating non-point source pollution. However, the impact of soil erosion on microplastic pollution in steeply sloped navel orange orchard was not fully understood. Here, we show how soil erosion impacts microplastic pollution and soil properties in navel orchard, and identify the relationship between microplastic distribution and soil properties. This study combined with field research and laboratory experiments to analyze soil properties distribution and microplastic transportation at different positions (non–erosion sites (NE), eroding sites (ME), and deposition sites (DS)) along four long slopes of navel orange orchard, including the control group (CK: sloping farmland near the sampling site), sloping orchard with 10°, 15°, and 25° slopes. Result showed that the clay content in the orchards exceeded that of CK, except on the 15° slope, where it increased from ME to DS across different slopes. Meanwhile, total nitrogen, soil organic carbon (SOC), nitrate nitrogen, and total phosphorus exhibited their lowest values at the ME and the highest at the DS across different slope positions. The soil erodibility was lowest at DS, while the comprehensive soil nutrient index was highest. The average microplastic abundance in the 10°, 15°, and 25° slope was 80.00, 68.89, and 78.89 items kg–1, respectively, showing comparatively lower than most orchards in China. Microplastic abundance was significantly positively correlated with SOC and clay (p < 0.05), whereas a significant negative correlation was observed with fine sand (p < 0.05). Our finding suggesting that soil erosion is one of the main driving forces behind microplastic migration and changes in soil properties, leading to their accumulation in DS. The findings offer empirical evidence of microplastic pollution in navel orange orchards. In future orchard management, replacing chemical fertilizers with farmyard compost could improve soil aggregation, strengthen root stability, and mitigate both soil erosion and the migration of microplastics.