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A Simple Spectral Index Using Reflectance of 735 nm to Assess Nitrogen Status of Rice Canopy

^a Div. of Crop Science, Taiwan Agricultural Research Institute, Wufeng, Taichung Hsien 413, Taiwan ROC; yjlee{at}wufeng.tari.gov.tw, cmyang{at}wufeng.tari.gov.tw
^b Dep. of Leisure and Recreation Studies, Aletheia Univ., Tainan Hsien 721, Taiwan ROC; ckw550320{at}yahoo.com.tw
^c Dep. of Soil & Environmental Sciences, National Chung-Hsing Univ., Taichung 40227, Taiwan ROC

View larger version (15K): [in this window] [in a new window]   Fig. 1. The typical canopy reflectance spectra (350–1,100 nm) collected in the panicle formation stage from rice plants (Oryza sativa cv. Tainung 67) grown under different application rates of N fertilizer at the Precision Agriculture Experimental Farm of Taiwan Agricultural Research Institute (Taichung Hsien, Taiwan) in first crop of 2001.

View larger version (18K): [in this window] [in a new window]   Fig. 2. Correlations between plant N concentrations (%) and the first derivative values of canopy reflectance spectra at 735 nm (dR/d|735) (A) and normalized difference vegetation index (NDVI) (B) measured at the panicle formation stage for rice plants (Oryza sativa cv. Tainung 67) grown under different application rates of N fertilizer at Chiayi Hsien in first crop of 2000 and at Taichung Hsien in first crop of 2001.

View larger version (24K): [in this window] [in a new window]   Fig. 3. Correlation between plant N concentrations (%) and the first derivative values of canopy reflectance spectra at 735 nm (dR/d|735) measured at the panicle formation stage for rice plants (Oryza sativa cv. Tainung 67) grown under different application rates of N fertilizer at Taipei Hsien, Taichung Hsien, Chiayi Hsien, and Pingtung Hsien in first or second crop from 2000 to 2002.

View larger version (31K): [in this window] [in a new window]   Fig. 4. Correlation between plant N concentrations (%) and simple ratio vegetation index (SRVI), normalized difference vegetation index (NDVI), (R1100 – R660)/(R1100+ R660), and R810/R560 measured at the panicle formation stage for rice plants (Oryza sativa cv. Tainung 67) grown under different rates of N fertilizer at Taipei Hsien, Taichung Hsien, Chiayi Hsien, and Pingtung Hsien in first or second crop from 2000 to 2002.

View larger version (22K): [in this window] [in a new window]   Fig. 5. Comparisons between the chemically analyzed and the model predicted N (%) from the spectral model derived from the N-dR/d|735 relationship for rice plants (Oryza sativa cv. Tainung 67) grown under different rates of N fertilizer at Taipei Hsien, Chiayi Hsien, and Pingtung Hsien in both first and second crops of 2002.

View larger version (55K): [in this window] [in a new window]   Fig. 6. (A) Maps of canopy N status of rice paddy obtained from three different regions of a rice field applied with different rates of N fertilizer, taken with a simplified imaging system unit mounted on a mobile lifter. (B) Validation of the relationships between the chemically analyzed and the image analyzed N (%) values from three different regions of a rice field applied with different rates of N fertilizer.

View larger version (39K): [in this window] [in a new window]   Fig. 7. Top: Maps of canopy N status of rice paddy obtained from three different regions of a rice field applied with different rates of N fertilizer, taken with a simplified imaging system unit mounted on a helicopter. Bottom: Validation of the relationships between the chemically analyzed and the image analyzed N (%) values from three different regions of a rice field applied with different rates of N fertilizer.