Abstract:Chinese cabbage was rapidly characterized using techniques of midinfrared spectroscopy (diffusion reflectance spectroscopy, attenuated total reflectance spectroscopy and photoacoustic spectroscopy). The results show that the characteristics of different infrared spectra of Chinese cabbage are significantly different, which are demonstrated by the appearance, position and relative intensity of absorption bands. For the midinfrared diffusion spectra, the main absorption bands are 2800-3800 cm-1, 2200-2500 cm-1, 1500-1700 cm-1 and 1000-1500 cm-1, for the attenuated total reflectance spectra there is only useful wavenumber region of 1200-1500 cm-1 due to the strong interference of water, and for the photoacoustic spectra the main absorption bands are 2800-3800 cm-1, 1500-1700 cm-1, 1200-1500 cm-1 and 1000-1200 cm-1. The principal components analysis of infrared spectra indicates the principal component distributions are related to the nitrogen application rate, and there are linearly correlations between the first principal component and the nitrogen application rate, the regression coefficients (R) for diffusion reflectance spectra, attenuated total reflectance spectra and photoacoustic spectra are 0.9103、 0.852 and 0.9366, respectively. Therefore, these three infrared techniques can be used in the rapid diagnosis of nitrogen nutrition of Chinese cabbage combining principal component analysis, and photoacoustic spectroscopy is more promising in the diagnosis of plant nutrition due to the convenient in situ measurement as well as depth profiling function.