估测水稻叶层氮浓度的新型蓝光氮指数

基于不同氮素水平与品种类型的多个田间试验，综合分析了水稻冠层高光谱植被指数与叶层氮浓度的定量关系.结果表明：对氮反应最敏感的波段为红光665～675 nm、蓝光490～500 nm和红边区域波段680～760 nm.400～2500 nm波段范围内两波段植被指数与水稻叶层氮浓度相关性最好的是550～600 nm与500～550 nm，属绿光波段组合，决定系数（R²）最高的是比值指数SR(533,565).以3个蓝光波段构建的光谱参数R₄₃₄/(R₄₉₆+R₄₀₁)（蓝光氮指数）与水稻叶层氮浓度呈极显著的直线相关关系，与SR(533,565)相比，该参数显著提高了对叶层氮浓度的预测性.独立资料检验结果显示，R₄₃₄/(R₄₉₆+R₄₀₁)对水稻叶层氮浓度具有较好的预测性，检验根均方差（RMSE）和相对误差（RE）值分别为9.67%和8%，是一种适合于水稻叶层氮浓度估测的良好高光谱植被指数.

A newly developed blue nitrogen index for estimating canopy leaf nitrogen concentration of rice

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.