Abstract:

A new method was developed for estimating the nitrogen nutrition of rice using continuum-removed reflectance. The most upper fully expanded leaves and the third fully expanded leaves were sampled during their important growth stages (tiller stage, booting stage and heading stage), and their concentrations of nitrogen and their reflectance measured. The value of the continuum-removed reflectance (550-750 nm) decreased as the nitrogen levels increased. Several properties of the continuum-removed reflectance spectra of fresh rice leaves 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 properties of the continuum-removed reflectance and leaf nitrogen concentrations. Stepwise multiple linear regression was used to select parameters that were most highly correlated with the nitrogen concentration of the leaf samples. Results of this research showed that total area of absorption peak was the best predictor of nitrogen levels in the third fully expanded leaves throughout their different growth stages (tiller, booting and heading stage). However, for the most upper fully expanded leaves, the significant model parameters included in the model were not always consistent. The basis for this method for diagnosing rice nitrogen nutrition on fresh leaves is not very clearly understood, but this research has demonstrated that continuum-removed reflectance is a feasible method.

Key words: Spectral reflectance, Continuum-removed, Nitrogen nutrition, Rice