Objective  Roles of phosphorus application on growth and root mycorrhizal infection rate of tomato seedlings intercropped with potato-onion were investigated to optimize the fertilization for sustainable crop production and agricultural ecosystem.

  Methods  Tomato (Solanum lycopersicum L.) seedlings were either grown under monoculture (T) or intercropping with potato-onion (Allium cepa L. var. aggregatum G. Don) (TO) in a pot experiment. Biomass, root mycorrhizal infection rate, and nutrient concentrations of the tomato plants, as well as the nutrient contents in the soil treated with varied phosphorus applications, i.e., 0 P (P0), 250mg P·kg⁻¹ (P250), 500mg P·kg⁻¹ (P500), and 1,000mg P·kg⁻¹ (P1000), were monitored.

  Results  Compared to P0, the dry weight of the monocultured tomato plant under P250 increased by 43.18%, under P500 by 47.73%, and under P1000 by 47.02%, while the intercropping under P250 resulted in an increase of 45.93%, under P500 50.36%, and under P1000 40.89%. At same P application level from T to TO, the tomato plant weight increased 8.8% under P0, 13.6% under P250, 15.2% under P500, and 5.6% under P1000. P250, P500, and P1000 enhanced the biomass production as well as the nutrient concentration and uptake of the tomato plants. The applications also increased the available P and K in soil with a significant positive correlation. At P500, the greatest and significantly higher than other treatments on plant biomass and root mycorrhizal infection rates of the tomato plants were observed.

  Conclusion  P played an important role in the interaction between tomato and potato-onion. At the 500 mg·kg⁻¹ application level, P maximized the interaction and enhanced the tomato root mycorrhizal infection which facilitated transfer of nutrients from soil to plant promoting the growth.