不同施氮处理下滴灌甜菜冠层的高光谱响应
Hyperspectral response of sugar beet to nitrogen fertilizer treatments in drip irrigation

为明确甜菜冠层高光谱特性，对不同氮素处理下滴灌甜菜冠层反射光谱以及叶面积指数（LAI）、叶绿素含量与叶片全氮含量进行分析。结果表明：甜菜冠层光谱反射率随着施氮量的增加而升高，与氮素运筹模式10∶0相比，氮素运筹模式7∶3的冠层光谱反射率和冠层光谱“红边”在叶丛快速生长期较低，在糖分积累期较高。甜菜冠层光谱红边具有“双峰”现象，且“双峰”随生育时期的推进逐渐减弱，随施氮量的增加，愈加凸显。光谱变量与叶片全氮含量显著相关，红边幅值Dλred、红边峰值面积Sred、红边位置λred与LAI、叶绿素含量显著相关，表明通过高光谱反演滴灌甜菜农学参数进行氮素营养状态诊断是可行的。
In order to better understand the hyperspectral characteristics of sugar beet canopy, the canopy reflectance spectrum and the total nitrogen content of the leaves were determined in a field experiment. The leaf area index (LAI) and chlorophyll content, the hyperspectral characteristics of sugar beet under different nitrogen fertilizer treatments were studied. Meanwhile, the correlation between the red edge parameters of the canopy and its spectral variables, and the total nitrogen content, LAI, and chlorophyll content were analyzed. The results showed that the spectral values of sugar beet were significant different among different growth stages, especially, in near infrared range (700~1 300 nm). The spectral reflectance of canopy under different nitrogen application rates were also significant different. In the rapid growth period of leaf cluster and increased with increasing nitrogen application rates. Conopy reflectance and “red edge” of nitrogen management model 7∶3 were lower than nitrogen management 10∶0 in the leaves rapid growth period, but higher in the sugar accumulation period. The red edge of beet canopy spectrum had a Twin-peak phenomenon, but the Twin-peak phenomenon gradually weakened with the growth and this change became more apparent with increasing nitrogen application rate. A significant correlation between the spectral variables and total nitrogen content of the leaves was observed. Additionally, the red edge amplitude Dλred, the red edge area Sred, and the red edge position λred, significantly correlated with LAI, and chlorophyll. Therefore, it is possible to diagnose nitrogen nutrition status of sugar beets by using hyperspectral variables of its canopy under drip irrigation.