Objective Soil erosion and nutrient loss are critical issues in steep-slope agricultural systems, especially in tea plantations where intensive land use often coincides with fragile ecological environments. Steep-slope tea cultivation not only alters the physical and chemical properties of soils but also modifies the balance between soil erodibility and nutrient cycling. Understanding the interaction between slope gradient and planting years is essential for predicting long-term soil quality dynamics and for developing strategies that support sustainable tea production, ecological management, and soil and water conservation.

Methods In this study, large-scale tea plantations in Shangnan county, Shaanxi province, were selected as the study area. A combination of field sampling and laboratory analysis was used to quantify soil erodibility and nutrient contents under different slope gradients (10°–40°) and planting years (1–20 years). Soil erodibility was calculated using the EPIC model, while soil nutrients, including ammonium nitrogen, nitrate nitrogen, total nitrogen, organic matter, and available phosphorus, were measured. Statistical analyses were employed to explore variation trends, and correlation analysis was performed to identify the key influencing factors of soil erodibility.

Results 1) Slope gradient strongly affected soil properties. As slope gradient increased, soil ammonium nitrogen, total nitrogen, organic matter, and available phosphorus exhibited a general decline, while nitrate nitrogen reached its maximum at 20°. Sand content showed a distinct "U-shaped" pattern, with the highest value (74.02%) observed at 40°. Correspondingly, soil erodibility peaked at 30° (0.028 4 t·hm²·h/(MJ·mm·hm²)), whereas at 40°, the high proportion of sand led to a significant reduction in erodibility. 2) Planting years also exerted a strong influence. With increasing planting years (10–20 years), vegetation cover increased substantially, and enhanced root activity combined with litter inputs promoted organic matter accumulation by 28.31%. This process effectively reduced soil erodibility. However, available phosphorus showed a continuous decline, reaching only 4.70 mg/kg at 20 years. Soil erodibility reached its highest value at 10 years but declined significantly by 20 years, at which point it was lower than that of the uncultivated control. 3) Correlation analysis further revealed that soil erodibility was positively correlated with clay, silt, total nitrogen, and available phosphorus, while showing a strong negative correlation with sand content.

Conclusions This study demonstrates that the dynamics of soil erodibility in steep-slope tea plantations are jointly regulated by slope gradient and planting years. Although vegetation recovery and litter input associated with longer cultivation can improve soil organic matter and reduce soil erodibility, the persistent decline in available phosphorus indicates a high risk of phosphorus depletion, which may constrain sustainable productivity. These findings highlight the importance of adopting integrated management strategies, including erosion control measures, optimized fertilization, and ecological restoration practices, particularly during the early stages of plantation establishment on steep slopes. This study provides a scientific basis for balancing agricultural development with ecological protection in mountainous tea-producing regions.