Potential of continuum removed reflectance spectral features estimating nitrogen nutrition in rice canopy level

A method was developed for estimating the nitrogen nutrition of rice (Oryza sativa) using canopy continuum-removed reflectance. The canopy leaves were sampled during important growth stages (tiller stage, jointing stage, booting stage and heading stage), and nitrogen concentrations and canopy reflectance were measured. The value of the continuum-removed reflectance (550nm-750nm) decreased with the nitrogen levels increased. Several characteristics of the continuum-removed reflectance spectra of rice canopy were calculated, including the continuum-removed reflectance value, the minimum of the continuum-removed absorption features, symmetry, total area of absorption peak and left area of the absorption peak. High correlations were found between the spectral characteristics of the continuum-removed reflectance and canopy leaves nitrogen concentrations. Linear regressions models were used to predicte nitrogen concentration. Results of this research showed that total area of absorption peak was the best predictor of nitrogen levels throughout growth cycle.