冬小麦特征光谱对其全氮和硝态氮的响应

Response of the spectral reflectance to total N and NO_3^--N of winter wheat

通过田间试验,测定了不同施氮水平下冬小麦冠层在6个典型生育期地上部分全氮和硝态氮含量以及冠层光谱,系统分析了单波段反射率、可见光和近红外波段组合而成的归一化植被指数(NDVI)、比值植被指数(RVI)等8种常见植被指数与相应时期地上部分全氮和硝态氮含量的相关性。结果表明,施氮量增加,全氮、硝态氮含量、冠层近红外波段反射率都随之增加,但当施氮量增加到300 kg/hm2(一次性施入)时,上述各项指标均降低;整个生长期中孕穗期在近红外区域反射率最高,与可见光波段反射率相差最大;6个生育期单波段510~1 100 nm反射率、NDVI、RVI等8种植被指数与全氮和硝态氮含量呈显著或极显著相关,植被指数的相关性较单波段高,且与全氮的相关性明显大于与硝态氮的相关性。选择NDVI(560 nm,760 nm)和NDVI(660 nm,760 nm)可以准确拟合冬小麦地上部分全氮和硝态氮含量,对前者的拟合度>0.80,对后者的拟合度>0.53。

In a field experiment that was conducted at six typical growth stages of winter wheat, we measured total N and NO3 ^- - N of above ground and canopy spectral reflectance in different N status, then analyzed the correlation between the single wavebands, NDVI/RVI and other vegetation indices that visible light and near infrared combined and total N, NO3 ^- - N concentration. The results showed that total N, NO3^ - - iN of above ground and canopy spectral reflectance in near infrared increased with the increasing of nitrogen rate until 300 kg/hm^2 （applied one-off） ; There was remarkable correlation between single wavebands from 560 nm to 1 100 nm, and the correlation coefficient of vegetation index was higher than single wavebands reflectance and increased from reviving to filling stage gradually, and the former was obviously better than the latter; The ability of NDV//RVI of 560 nm and 660 nm in visible light and 760 nm, 1 100 nm and 1 200 nm in near infrared combined were better than other wavelengths. NDVI（560 nm, 760 nm） could estimate the content of above ground total iN and NO3 ^- - iN accuracy. These results indicated that canopy spectral reflectance could be used to non-destructively monitor N status in winter wheat.