Hyperspectral evaluation of rape nitrogen nutrition using continuum-removed method

The hyperspectral reflectance for fresh rape leaves and total nitrogen content were acquired at primary growth stages under different nitrogen levels. A new method was developed for estimating the nitrogen nutrition of rape using continuum-removed method, which generally used in spectra analysis of rock and mineral. Based on the continuum-removed treatment and the correlation between absorption feature parameters and total nitrogen content of fresh leaves, results show that reflectance at visible region decrease with the increase of the nitrogen fertilization, and continuum-removed operation can magnify the subtle difference in spectral absorption characteristics arisen from the nitrogen stress on rape. During the seeding stage, bud-emerging stage and flowering stage of rape, total area of absorption peak, left area of the absorption peak and right area of the absorption peak in 550～750 nm region increased with the increase of the nitrogen fertilization, but it was opposite for the normalized maximal absorption depth. The correlation analysis indicated that it is at the seeding stage that the relation ship between absorption characteristics parameters and leaf total nitrogen is the most closely significant. In addition, the regression models were made between all absorption characteristics parameters and total rape nitrogen, and the models were all at 1% significance level except the bud-emerging stage. The research demonstrates that continuum-removed method is a feasible method for quantificational evaluation of rape nitrogen nutrition, and seeding stage of rape is the best stage for assessment of rape nitrogen nutrition based on absorption characteristics of fresh leaves.