Spectral indices redefined in detecting nitrogen availability for wheat canopy
2004
Zhao, C. | Zhou, Q. | Wang, J. | Huang, W.
Spectral indices (simple ratio: SR, normalized difference vegetation index: NDVI, and photochemical reflectance index: PRI) redefined on the basis of the actual wavelength of maximum or minimum reflection were related to biophysical variables such as leaf area index (LAI), leaf chlorophyll concentrations, and dry phytomass of wheat plants subjected to six levels of nitrogen (N) fertilization. The wavelength of peak reflection in the green band was at about 554 nm and that of minimum reflection in the red band was at about 670 nm for wheat canopy. The shift from 680 nm to 670 nm in the red band had a minor effect on spectral signature indicated by SR and NDVI, which had a strong positive relation with LAI and leaf chlorophyll concentration. PRI appeared to be best related to dry phytomass. The redefined spectral indices were not better related to the biophysical parameters. The redefined PRI (PRI-re) based on 554 nm appeared to be the most sensitive indicator of N availability for wheat canopy. Generally, canopies of low N availability could be characterized with low SR (NDVI) values and low PRI-re values. The canopies with excess N fertilization had medium values of SR (NDVI) and PRI-re.
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