Construction of critical phosphorus concentration dilution curve and phosphorus nutrition diagnosis of winter wheat in Guanzhong plain

Objectives Based on the relationship between winter wheat phosphorus application rate and wheat phosphorus nutrition in Guanzhong Plain, we established a critical phosphorus concentration dilution curve to provide a theoretical basis for meeting the P needs of local winter wheat.

Methods The long-term localization phosphorus field experiment was established in 2009, and the wheat variety was Xinong 979. The four phosphorus application treatments (P₂O₅) tested were 0, 60, 120, 180 kg/hm², noted as P0, P60, P120 and P180, respectively. The above-ground plant samples were determined at the jointing, booting, flowering, filling, and maturity periods of the winter wheat from 2018 to 2021, and the above-ground biomass and plant phosphorus concentration were analyzed, the wheat yield was also evaluated. A critical phosphorus concentration dilution model was used to calculate the P nutrient index (PNI). The reliability of phospho-nutrition index was verified based on winter wheat data from 2020 to 2021.

Results 1) P fertilization significantly increased the panicle number in three seasons by 50.7%–53.0%, 23.1%–29.7%, and 17.5%–19.0%, increased the grain number per panicle by 28.6%–34.2%, 22.7%–24.1% and 18.7%–19.6%, but reduced 1000-grain weight by 1.1%–2.9%, 3.5%–7.0% and 1.3%–4.9%, respectively. The panicle number elicited by P120 and P180 treatments were similar. With the increase in P application rate, the grain yield increased first and then decreased, and the yield in the three seasons was increased by 104.3%–108.2%, 39.8%–47.4%, and 27.6%–32.5% on average, with the maximum yield of 7100 kg/hm², 6369 kg/hm², and 6714 kg/hm² under the P120 treatment. 2) The aboveground biomass of winter wheat gradually increased with the progress in the growth process, and the P concentration in the upper aboveground part gradually decreased. Based on the aboveground biomass and P concentration of winter wheat in 2019—2020, a critical P concentration dilution curve model was established: P_c=6.00DM^–0.43, with the RMSE of 0.09, and n-RMSE of 3.45%, indicating that the reliability and stability of the model simulation values meet the requirements. 3) The PNI of wheat was mainly affected by P application rate, not by growing stage. P120 treatment had the PNI closest to 1.

Conclusions Based on above-ground biomass and P concentration of winter wheat under different P application rates, the critical phosphorus concentration dilution curve model and P nutrition index (PNI) model can ideally diagnose the status of phosphorus, balance in winter wheat in Guanzhong plain, and can be used as a tool for phosphorus content assessment and guidance of phosphorus fertilizer application.