Abstract: Based on the field experiments with different rice varieties and nitrogen application rates, a comprehensive analysis was made on the quantitative relationships between hyperspectral vegetation indices of rice canopy and its leaf nitrogen concentration (LNC) at different rice growth stages. The wave bands most sensitive to the canopy LNC were in red region (665-675 nm), blue region (490-500 nm), and red edge region (680-760 nm). Within the range of 400-2500 nm, the wave bands showing the best relationships between rice canopy vegetation indices and LNC were 550-600 nm and 500-550 nm in green region, and the ratio index SR(533,565) had the highest value of determination coefficient (R²). However, the spectral parameter established with three wavelengths in blue region, i.e., blue nitrogen index R₄₃₄/(R₄₉₆+R₄₀₁), had a significant linear relationship with the canopy LNC, and made the prediction accuracy of the canopy LNC promoted significantly, compared with SR(533,565). The tests with independent datasets showed that R₄₃₄/(R₄₉₆+R₄₀₁) was a reliable indicator of rice canopy LNC, with the RMSE and RE values between measured and estimated LNC being 9.67% and 8%, respectively. Therefore, the newly developed blue nitrogen index R₄₃₄/(R₄₉₆+R₄₀₁) was recommended as a good indicator of rice canopy LNC.

Key words: rice, canopy leaf, nitrogen concentration, hyperspectral vegetation index, blue nitrogen index ［R₄₃₄/(R₄₉₆+R₄₀₁)］, tillage, straw returning, microbial community, enzyme activity, grain yield.