Abstract:

It is very important for using nondestructive method to determine nitrogen status and growth characters of crop plants. Three experiments were carried out in Nanjing to investigate the quantitative relationships of leaf nitrogen accumulation to canopy reflectance spectra in wheat. 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 application levels of 0, 75, 150, 225 and 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 accumulation in wheat leaves was increased with increasing nitrogen application. For the different cultivar types with low, medium and high grain protein contents, the correlations were higher for leaf nitrogen accumulation per unit soil area to canopy reflectance spectra. The ratios of several bands in near infrared to visible light were linearly related to leaf nitrogen accumulation, and thus the ratio index of the average reflectance at 760, 810, 870, 950 and 1 100 nm to 660 nm was used for quantitative monitoring of leaf nitrogen accumulation in the different cultivar types, but different cultivar types had different regression coefficients. The above dynamic relationships of leaf nitrogen accumulation 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 accumulation, Canopy reflectance spectra, Spectral index, Quantitative relationship