Quantitative relationship between leaf nitrogen accumulation and canopy reflectance spectra in wheat

Chinese. 利用不同小麦品种在不同施氮水平下的3年田间试验数据，研究了小麦叶片氮积累量与冠层反射光谱间的定量关系。结果显示，不同试验中拔节后叶片氮积累量均随施氮水平呈上升趋势，同时冠层光谱反射率在不同施氮水平下存在明显差异。对于低、中、高蛋白质含量的品种类型，近红外区域若干相邻波段和可见光波段组成的比值植被指数与单位土地面积上叶片氮素积累量的相关关系均表现较好，因此可用760、810、870、950和1100nm反射率的平均值与660nm组成的比值植被指数对不同蛋白质类型小麦品种的叶片氮素积累量进行定量监测，但回归方程的斜率在不同类型品种之间存在显著差异。本研究确立的小麦叶片氮积累量与冠层反射光谱的定量关系可用于不同的小麦品种、生育时期和施氮水平，为小麦氮素营养的监测诊断与精确施肥等提供理论依据和技术途径。

English. 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 relationship of leaf nitrogen accumulation to canopy reflectance spectra in wheat. Experiment one was conducted with two cultivars （Xuzhou 26 and Huaimai 18） and four nitrogen application levels of 0, 120, 210 and 300 kg/ha in 2001. Experiment two was designed for one cultivar （Yangmai 10）, with three nitrogen application levels of 0, 150 and 300 kg/ha 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 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 cuhivars were thought to be medium-protein type. The results showed that the nitrogen accumulation in wheat leaves 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 1100 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.