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• Mild soil erosion (0–176.26 t hm−2 a−1) occurred in the Nanliao River watershed. • Soil total P (STP) content showed moderate variability (0.06–1.19 g/kg). • There was a negative correlation between STP content and soil erosion. • Elevation, soil particle size, and pH were the main factors influencing STP content. Soil erosion can change the migration and deposition patterns of soil particles and alter the regional geographic environment; therefore, it plays an important role in the biogeochemical cycle of soil total phosphorus (STP). Quantifying the influence of environmental factors on STP content under soil erosion is critical for understanding the lateral transfer of STP from soil. Here, we explored the influence of environmental factors on STP content under different levels of soil erosion in the small watershed of Nanliao River, a tributary of Xiu River in the western part of Poyang Lake Plain in Jiangxi Province, China. Soil erosion ranged from 0 to 176.26 t hm−2 a−1 (15.41 t hm−2 a−1 on average) across the watershed in 2018, indicating a mild erosion level on the whole. The STP content varied between 0.06 and 1.19 g/kg (0.6 g/kg on average) with a coefficient of variation of 43.33%, indicating moderate variation. An exponential model with a small nugget effect (7.35%) and a small range (2.25 km) could estimate 86.5% of spatial variability in STP content. The STP content showed a strong spatial autocorrelation, and the soil rich in STP was mostly distributed along the Nanliao River. There was a negative correlation between STP content and soil erosion (r = –0.149, P < 0.01). Each of the 10 selected environmental factors could explain 2.7–21.3% of spatial variability in STP content. Elevation, soil particle size, soil pH, and their interactions with other factors were the main factors influencing STP content, although their influence differed across various erosion levels. This study could provide useful data for controlling STP loss and reducing the impacts of soil erosion on the ecological environment in the Poyang Lake Plain. [ABSTRACT FROM AUTHOR]