Fig. 1. Distribution of experimental plots the study site

Fig. 2. Technical flow chart for the winter wheat total nitrogen content (TNC) prediction based on XGBoost

Fig. 3. Canopy spectra of winter wheat at different fields

Fig. 4. Correlation coefficient of spectral reflectance and TNC

Fig. 5. Scatter plots between the predicted TNC and measured TNC

Fig. 6. Spatial distributions of TNC predicted by XGBoost

Fig. 7. Correlaion between TNC in winter wheat and TNC in soil