Journal of Taiwan Agricultural Research

Author:Yuh-Jyuan Lee, Chwen-Ming Yang* and Ay-Hwa Chang

Abstract:

    Field experiments were conducted in the experimental farm of Taiwan Agricultural Research Institute, Wufeng, to study changes of nitrogen and chlorophyll contents and spectral characteristics to the application of nitrogen fertilizer in rice plants (Oryza sativa L. cv. TNG67) grown in the first and the second cropping seasons of 1999. It was shown a higher level of soil nitrogen in the soil applied with nitrogen fertilizer. Nitrogen and chlorophyll contents in leaves and aboveground plant parts of rice from the fertilized plots were greater than that in the plants from the non-fertilized plots during both growing seasons. Nitrogen and chlorophyll were shown curvilinearly correlated. Plants supplied with fertilizer had higher leaf area, aboveground fresh weight and plant height, especially in the first crop. Reflectance spectrum of rice canopy was affected by the application of nitrogen fertilizer with the distinct differences in the near-infrared waveband (740-1100 nm) from panicle initiation to heading stage in particular. By the correlation intensity analysis, it indicated that reflectance in blue and near-infrared wavebands were closely correlated to leaf nitrogen content. The highest correlation coefficient was located at 720 nm and 708 nm for the first and the second crops, respectively. The relationship between reflectance and leaf nitrogen at these two wavelengths was best fitted to the curvilinear function, with the determining factors (R²) of 0.856 (First crop) and 0.550 (Second crop), respectively. The waveband ratios of G/R, NIR/R, NIR/G, and NDVI (normalized difference vegetation index) were curvilinearly distributed during rice growth in both crops with the plateau in the panicle formation stage. The ratios were found higher from the fertilized plants, with NIR/G and NIR/R as better indicators.

Key words:Rice, Nitrogen, Chlorophyll, Spectral characteristics, Waveband ratio, Vegetation index

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