Objective This study aimed to explore the effects of slope length on soil and water erosion and nitrogen-phosphorus (N-P) loss characteristics on mining slopes, in order to predict soil nutrient loss on mining slopes and provide a theoretical basis for formulating measures to prevent and control soil and water erosion in mining areas.

Methods The effects of three types of slope lengths (2 m, 3 m and 4.5 m) on the flow, sand and nitrogen (N) and phosphorus (P) loss characteristics of mine slopes under the same slope gradient and rainfall intensity were analyzed by simulating rainfall artificially and constructing a prediction equation of “N and P nutrient loss rate - flow rate/sand production rate”.

Results ① Compared to the 2 m slope, the initial runoff time for the 4.5 m and 3 m slopes was advanced by 51.2% and 18.6%, which indicates a negative correlation between slope length and initial runoff time. ② The runoff yield at 3 m and 4.5 m slope lengths increased by 1.56 and 2.47 times compared with the 2 m slope length. The cumulative runoff yield on each slope showed a power function trend of increase with the increase of rainfall duration. The sediment yield at 3 m and 4.5 m slope lengths increased by 2.17 and 2.73 times compared with the 2 m slope length. The cumulative sediment yield on each slope showed a significant positive correlation with rainfall duration. ③ Total P (TP) loss via runoff accounted for only 6% - 7% of the total TP loss, indicating that P was primarily transported through sediment. In contrast, total N (TN) loss via runoff was 1.05 - 2.04 times higher than that via sediment, suggesting N predominantly migrated through runoff. ④ The predictive equations for the rate of N and P nutrient loss rate-production rate on the slope surface were: L_TP = 0.137R + 0.072 (R² = 0.821), L_TN = 2.869R +5.38 (R² = 0.731); N and P nutrient loss rate- sediment production rate prediction equation: D_TP = 2.132E + 0.392 (R² = 0.804), D_TN = 0.981E + 0.446 (R² = 0.795).

Conclusion In the case of a rainfall intensity of 80 mm h⁻¹ and a slope gradient of 10°, the shortening of the length of the slope will to a certain extent reduce the loss of soil, N and P nutrients from the slope face of the mining, the N and P loss rate from the soil and the slope face flow production, and the rate of sand production show a significant positive correlation. The prediction equation can effectively predict the N and P loss of single factor of slope length through the rate of slope flow and sand production.