Objectives This study aimed to establish, modify, and validate the critical phosphorus concentration dilution curve (CPNDC) of spring wheat under drip irrigation, providing a feasible tool for phosphorus nutrition diagnosis and fertilizer recommendation in drip-irrigated spring wheat production in Xinjiang.

Mothods Field experiments were carried out in Shihezi City of northern Xinjiang in 2023 and 2024, using the spring wheat cultivar Xinchun 44. Designed five P₂O₅ application rates were 0, 30, 90, 150, and 210 kg/hm². Since the three-leaf stage of wheat, the aboveground dry matter mass and P content of spring wheat were analyzed regularly. The data of 2023 were used for the establishment of CPNDC model, and the phosphorus nutrition index (PNI) of wheat was calculated. In 2024, an independent drip irrigation field experiment of spring wheat was set up to verify the availability of P recommendation using the established CPNDC model. In the experiment, conventional P management (P₂O₅ 150 kg/hm², 80% basal applied and 20% topdressed) was used as control, three phosphorus fertilizer application rates of PR0.8, PR1 and PR1.2 were designed, and all topdressing treatments were carried out to verify the applicability of the model in guiding the topdressing of phosphorus fertilizer.

Results The established and modified CPNDC model for spring wheat under drip irrigation in this study was: Pc=0.845×DM^−0.201, R²=0.9405. The RMSE and n-RMSE of the model were 0.045 and 8.105%, indicating the high accuracy and stability of the model. The PNI did not changed significantly with the increase of phosphorus application rate at all the sampling stages. The yield of spring wheat at PR1.2 was 9132 kg/hm², which was not significantly different from that of control, while the yield at PR0.8 and PR1 treatments were significantly lower than the control. All the three PR treatments increased the harvest index, phosphorus fertilizer utilization rate and phosphorus fertilizer partial productivity.

Conclusions The CPNDC model and phosphorus nutrition index (PNI) of drip-irrigated spring wheat established in this study can well predict the phosphorus profit and loss status of plants at different growth stages, and it is feasible to guide the phosphorus nutrition diagnosis of drip-irrigated spring wheat in Shihezi area of Xinjiang during the growing season and the optimal phosphorus fertilizer application rate. Might due to the changed application method, phosphorus fertilizer at 1.2 times of the recommendation rate could maintain the wheat yield. Even though, the phosphorus fertilizer rate will be reduced greatly.