Development of Nitrogen Fertilizer Topdressing Model for Winter Wheat Based on Critical Nitrogen Dilution Curve

Critical nitrogen (Nc) dilution curve and its extended N nutrient index (NNI) in previous study was only be applied to wheat for N status diagnosis. This research improved this model and further established the N topdressing model which can be quantify the N topdressing rate when NNI < 1. To facilitate the estimate of the Nc concentration, the determination of basal stem tissue sap nitrate (Nit) concentration as a rapid and operational way was used to characterize N status in this study. The results revealed that N dilution curve in this study specific to winter wheat could be used to establish the N nutrition status. There was significantly positive relationship between the Nit concentration and whole plant N concentration at each growth stage. Moreover, the Nit concentration linearly and positively correlated to the N fertilizer application rate, then deducing the N fertilizer topdressing rate per 100 Nit unit, which finally established the N fertilizer topdressing model: N topdressing rate = (critical Nit − actual Nit) × N topdressing rate per 100 Nit unit. The N dilution curve-based model will offer technical support for managing the precise application of N during the growth period of wheat crops.