系统分析了不同时相下两个小麦(Triticum aestivium)品种叶片含氮量及叶片氮积累量与冠层光谱反射特征的关系。结果表明，随施氮水平的增加，小麦冠层在可见光区的反射率逐渐降低，而近红外波段的反射率逐渐升高。小麦叶片氮素状况与比值指数或归一化指数显著相关，两个品种表现极为一致，可以用一个指数方程来拟合。分阶段建模并没有提高模型的精度，因此可以建立一个适用于整个生育时期的通用氮素诊断方程。叶片含氮量同光谱指数在整个生育期内的关系要优于叶片氮积累量的，其中，与叶片含氮量关系最佳的指数为红波段(660 nm)和蓝波段(460 nm)的组合(R2>0.80)；与叶片氮积累量关系最佳的光谱指数为中红外波段(1 220 nm)与红波段(660 nm)的组合(R2>0.62)。
Non-destructive monitoring and diagnosis of plant nitrogen (N) status is necessary for precision N management. The present study was conducted to determine if canopy reflectance could be used to evaluate leaf N status in wheat (Triticum aestivium) of two cultivars, `Huaimai 18‘ and `Xuzhou 26‘. Ground-based canopy spectral reflectance, leaf N concentration and leaf N accumulation were measured at seven growth stages (jointing, booting, heading, anthesis, initial filling, mid-filling and late filling) under four different treatments of N fertilization (0, 12, 21 and 30 g N·m-2). Analyses were made on the relationships of seasonal canopy spectral reflectance, ratio indices (R(λ1,λ2)=ρλ1/ρλ2) and normalized difference indices (ND(λ1,λ2)=|ρλ1－ρλ2|[]ρλ1+ρλ2) to leaf N concentration and N accumulation in wheat under different N treatments at different growth stages and during the whole growing season. The results showed that canopy spectral reflectance in the near infrared increased with increasing N content, whereas reflectance in the visible band decreased. Leaf N status was significantly correlated with the ratio or normalized difference indices in both cultivars. Regression models of leaf N status to spectral indices based on single growth stages did not improve the prediction over whole growth cycle; hence, a single regression model based on the whole growth cycle should be adequate for diagnosing N status in wheat plants. The relationships between leaf N concentration and spectral indices were better than those of leaf N accumulation. The best indices were the combination of a MIR (mid-infrared) band (1 220 nm) and red band (660 nm) for leaf N concentration (LNC=3.894 5×R(660, 460)-1.028 7, R2=0.834 2; LNC=3.918 7×e-2.179 6ND(660,460), R2=0.835 2) and the combination of the red band (660 nm) and blue band (460 nm) for leaf N accumulation LNA=1.55×e0.115 3R(1 220, 660), R2=0.724 2; LNA=0.219 4×e4.091 4ND(1 220, 660), R2=0.629 9). These results indicate that canopy spectral reflectance can be used to non-destructively monitor leaf N status in wheat plants.