Objectives We investigate the effects of P fertilizer application on N uptake and distribution with the aim of providing information on optimal N and P nutrient management in maize and soybean intercropping system.

Methods A two-year pot experiment involving three planting patterns (monocropped maize, monocropped soybean, maize and soybean intercropping) and four P₂O₅ rates (0, 50, 100, and 150 mg/kg, expressed as P0, P50, P100 and P150) was conducted. Maize samples were collected at the small belling, big belling, booting, and maturity stages. Soybean samples were collected at the branching, flowering, podding and maturity stages. The collected samples were analyzed for N uptake and distribution in different organs of maize and soybean. The response of N uptake under intercropping and its advantage under P fertilizer application was evaluated.

Results Compared with monocropping, intercropping significantly increased the grain biomass of maize and soybean under P0, P50, P100 and P150 levels by 38.2%–111.8% and 22.2%–31.4% in 2019, and 38.2%–121.1% and 13.0%–31.1% in 2020, respectively. Land equivalent ratio (LER) was 1.31–1.72 under maize and soybean intercropping systems at the four P levels. The grain yield of intercropped maize and soybean did not decline in the P50 treatment, compared to the corresponding monocropping in the P100 treatment. Intercropping increased the N uptake of leaves, stems, roots, and grains of maize and soybean and significantly increased the N uptake of the intercropping system. Intercropping promoted N allocation to maize grains but decreased that to soybean grains. Compared with P0 treatments, P fertilization further increased N uptake in all organs of intercropped maize and soybean, had an intercropping advantage, and promoted N allocation to maize grains. Meanwhile, the N uptake and utilization efficiency of intercropped maize and soybean under P50 level did not reduce compared to monocropped maize and soybean under P100 level.

Conclusions Maize and soybean intercropping showed a significant yield advantage. Phosphorus fertilization could increase the N uptake of maize and soybean intercropping systems and promote the allocation of N to maize grains, showing a substantial benefit of N uptake under intercropping. P application rates alleviated the competition for N between maize and soybean and led to higher N fertilizer efficiency.