Effects of phosphorus application and rhizobial inoculation on nitrogen and phosphorus uptake in soybean||maize intercropping systems in different soil types

A pot experiment was conducted to compare the effects of rhizobial inoculation on growth, nitrogen (N) and phosphorus (P) uptake, and rhizosphere chemical properties of soybean Glycine max (L.) Merr. and maize (Zea mays L.) intercropping systems with different P fertilizer applications in both acidic and calcareous soils, to provide a reference for the field application of rhizobial inoculants. The pot experiment with ‘BX10’ soybean variety and ‘Zhengtian 68’ maize variety as experimental materials adopted a three-factor experimental design, including factor A, P levels with P fertilizer (+P) and without P fertilizer (–P); factor B, two soil pH types (acid soils form Ningxi and Wengyuan, and calcareous soils form Sanping and Changping); and factor C, two inoculation treatments with rhizobial inoculation (+Ri) or without rhizobial inoculation (–Ri). The nodule traits of soybean, plant dry weight, total N and P uptake, and related rhizosphere traits of soybean and maize were determined at the pod stage of soybean. The results showed that inoculation with rhizobia increased the total N uptake of the intercropped soybean under P application in acidic soil, and inoculation with rhizobia improved nodule traits and increased total N uptake of the intercropped soybean regardless of P application and promoted total P uptake of the intercropped soybean in calcareous soil. In both calcareous soils, the total P uptake of the inoculated soybean plants increased significantly. In the calcareous soil of Sanping, the rhizosphere pH was significantly reduced and the rhizosphere acid phosphatase activity of the inoculated soybean significantly increased after rhizobial inoculation and P application. In the calcareous soil of Changping, the rhizosphere alkaline phosphatase activities of intercropped soybean and maize significantly increased after inoculation with rhizobia under P application. With increased total N and P uptake, rhizobial inoculation increased the plant dry weight of intercropped soybean in calcareous soil but had no effect on plant dry weight and total N and P uptake of intercropped maize. In conclusion, soil pH and P availability significantly influenced the effectiveness of rhizobial inoculation. In acidic soil, inoculation with rhizobia increased the total N uptake of intercropped soybean under P application. In calcareous soil, inoculation with rhizobia could promote the synergistic effects of N and P and further promote the growth of intercropped soybean. The promotion of P mobilization and acquisition by rhizobial inoculation might be attributed to the enhancement of rhizosphere processes in calcareous soil.