Abstract:

Experiment one was conducted with two cultivars (Xuzhou 26 and Huaimai 18) and four N application levels of 0, 120, 210 and 300 kg·ha^-1 in 2001. Experiment two was designed for one cultivar, Yangmai 10, with three N application levels of 0, 150 and 300 kg·ha^-1 in 2002. Experiment three included four cultivars (Xuzhou 26, Huaimai 20, Ningmai 9 and Yangmai 10) with five nitrogen levels of 0, 75, 150, 225, 300 kg·ha^-1 in 2003. On the basis of characterized protein content of these five cultivars, Xuzhou 26 and Ningmai 9 were considered as high and low protein types, respectively, and the other three cultivars were thought to be medium-protein type.
The results showed that the nitrogen concentration in wheat leaves was increased with increasing nitrogen fertilizer, whereas the canopy reflectance was also significantly different under varied nitrogen application. For the different cultivar types with low, medium and high grain protein contents, the relationships of leaf nitrogen concentration to NDVI (1220, 710) and red edge position of canopy reflectance spectra were all highly significant with R2 of 0.80(Fig.1 and Fig.2). An integrated regression equation could be used to describe the dynamic change pattern of leaf nitrogen concentration with reflectance spectra parameters in different cultivar types, although separate regression coefficients enhanced the prediction accuracy in low protein type. The above dynamic relationships of leaf nitrogen concentration to canopy reflectance spectra were feasible for different cultivars, growing stages and nitrogen levels in wheat. These results provide a theoretical basis and technical approach for monitoring of plant nitrogen status and precision management of nitrogen fertilization in wheat production.

Key words: Wheat, Leaf nitrogen concentration, Canopy reflectance spectra, Spectral index, Quantitative relationship