Critical nitrogen (N c ) 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 N c 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.

中文翻译：

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基于临界氮稀释曲线的冬小麦追施氮肥模型开发

以往研究中的临界氮（N c ）稀释曲线及其扩展的氮营养指数（NNI）仅适用于小麦的氮状况诊断。本研究对该模型进行了改进，进一步建立了可以量化 NNI < 1 时的 N 追施速率的 N 追施模型。 为了便于估计 N c 浓度，将基部茎组织液硝酸盐 (Nit) 浓度的测定作为一种快速的方法。在本研究中，使用操作方法来表征 N 状态。结果表明，本研究中针对冬小麦的氮稀释曲线可用于确定氮营养状况。各生长阶段Nit浓度与全株N浓度呈显着正相关。而且，Nit 浓度与施氮量呈线性正相关，然后推导出每 100 Nit 单位追施氮肥量，最终建立氮肥追施模型：氮肥追施量=（临界 Nit - 实际 Nit）×N 追施量每 100 尼特单位。基于氮稀释曲线的模型将为小麦作物生育期精确施氮管理提供技术支持。