Leaf Spectral Characteristics and Its Sensitivity to N in Different Vegetative Growth Stages of Turnips

【Objective】 The sensitive period of leaf spectral index was studied by analyzing the leaf spectral reflectance in the response to Nitrogen (N) fertilizer at different growing stages of different turnip cultivars in Xinjiang aiming to provide a non-invasive,simple and rapid nutrition diagnosis of N.【Method】The spectral reflectance of different turnip seedling stages, leaf growth exuberant stage, fleshy root growth peak stage and mature stage were measured by Unispec-SC spectrometer with different turnip cultivars as the test material.【Result】The fluctuation of leaf spectral reflectance of different turnip cultivars depended on the wavelengths at all the growing stages,and the least variation was in the range of visible wavelength. The leaf spectrum indexes (ND₇₀₅) of different turnip cultivars were significant (P < 0.05) and extremely significant (P < 0.01) different at all growing stages.【Conclusion】Spectral sensitive period of foliar N concentration varied during different growing stages. The sensitive period for leaf spectral nutrition diagnosis in response to N of long and yellow turnip, Xinxing round turnip, American turnip and Tiandihe turnip were leaf exuberant growth period. The sensitive period for leaf spectral nutrition diagnosis in response to N of Xinxing round turnip (second generation) turnip are leaf exuberant growth period and fleshy root growth stage. The seedling stage and fruit mature period can be used to distinguish several varieties of turnip diagnosis of nitrogen sensitive growth stage.