Effects of legume intercropping and nitrogen application on soil phosphorus availability and leaf nutrient status in subtropical Camellia oleifera plantations

• Legume intercropping boosts labile P in acidic soils and leaf nutrient uptake. • Low N application enhances soil P availability and plant uptake. • High N initially reduces labile P but partially recovers at maturity. • Intercropping increases soil organic carbon, nitrate N, and phosphatase activity. • Both legumes intercropping and low N improve P cycling and crop nutrition. Phosphorus (P) availability is often limited in subtropical acidic soils due to fixation by iron and aluminum oxides, constraining nutrient uptake and productivity in Camellia oleifera plantations. However, the mechanisms by which the effects of artificial nitrogen (N) application and natural N fixation via legume intercropping on soil P dynamics remain poorly understood. In this study, the independent effects of legume intercropping and N application on soil P fractions, soil biochemical properties and leaf nutrient content were investigated in C. oleifera plantations in subtropical China. Six treatments were applied: monoculture with weeding, monoculture without weeding, intercropping with Cassia tora or peanut, and monoculture with low or high N application (25 or 50 g urea per plant). Soil P fractions, soil organic carbon, total N, pH, ammonium (NH 4 + -N), nitrate (NO 3 − -N), acid and alkaline phosphatase activities, and leaf C, N, and P contents were measured at the growth (July) and mature (September) stages. Results showed that both legume intercropping and low N application independently enhanced total and labile soil P, increased soil organic carbon, and improved leaf nutrient contents compared to the control. High N initially reduced labile P but partially recovered by maturity. Phosphatase activities declined at maturity but remained higher in intercropped and fertilized plots, indicating improved P cycling. Nitrate N concentrations increased from the growth stage to the mature stage. These results suggest that legume intercropping and N application, when applied independently, each promote soil P availability and plant nutrient uptake, highlighting practical strategies to enhance soil fertility and sustain C. oleifera production in subtropical acidic soils.