Abstract:Nitrogen nutrition status of winter wheat was close related to its quality and yield. Conventional chemical method for plant nutrition diagnosis was considered as a reliable one. However, it was time-consuming which limited its wide application in agricultural production. In recent years, the Chlorophyll meter method has been adopted to access the N status of crops, however, the content of chlorophyll is not only related to the rate of nitrogen supplied, but also to crop characteristics. In order to using this method to conduct a rational application of N, an ulterior study of mutual relation between crop variety as well as growing stage and SPAD reading was quite necessary, especially for the wheat production on the dryland of Northwest China. A field experiment was conducted to study the relationship between the varieties of winter wheat as well as the application rates of nitrogen and the SPAD reading at different growing stages of winter wheat. The experimental design was split-plot design. Results showed that SPAD values were high correlated to the biological yields and grain yields of winter wheat, especially at the jointing stage and anthesis stage. There was also a significantly positive correlation between the SPAD value and the application rate of N. The SPAD value was the highest when the nitrogen application rate was 180 kg/ha. Under the condition of same application rate of N, the SPAD value was the highest at anthesis stage. The (discrepancies) of the SPAD value among different wheat varieties were less before jointing stage; while discrepancies were much more after jointing stage, with highest discrepancy being 9.2 SPAD units. The SPAD value of Xiaoyan22 was the highest at each stage. The discrepancy between Xiaoyan22 and Shaan253, Shaan229 as well as Xiaoyan503 measured up to a significant level at each growth stage. This indicated that different varieties had different responses to N. Therefore, it is necessary to set up different diagnosis indexes corresponding to different variety of winter wheat.