Abstract: Crop nitrogen status is a key indicator of crop growth, yield production, and grain quality, and of significance in crop nitrogen diagnosis and manage
ment. Based on the data of winter wheat canopy spectra and corresponding leaf nitrogen accumulation (LNA) acquired under different nitrogen application levels,
the nitrogen nutrition of crop canopy was evaluated by continuum-removed method, a widely used method in spectra analysis of rock and mineral. Three absorption features were acquired by the continuum-removed treatment of canopy spectra ranging from 550 nm to 760 nm. The LNA at all growth stages increased with increasing nitrogen fertilization; but under the same levels of nitrogen application, the LNA increased from erecting stage to booting stage, and decreased from booting stage to heading stage. At all growth stages, the total area of absorption peak (TA), left area of absorption peak (LA), and right area of absorption peak (RA) increased with increasing nitrogen fertilization, whereas the normalized maximal absorption depth by area (NMAD) decreased. All the absorption feature parameters of continuumremoved spectra had significant correlations with LNA, and the relationship between NMAD and LNA was the best. The correlations in whole growth period were higher than that at any growth stage. From the viewpoint of growth stage, booting stage was the best growth stage to monitor the LNA. Regression analysis displayed that the LNA regression model based on the whole growth period was most available.

Key words: Dissolved Organic Matter (DOM), Soil, Heavy metal, Bioavailability